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How to Create an APA Style Appendix | Format & Examples

Published on October 16, 2020 by Jack Caulfield . Revised on August 9, 2022.

An appendix is a section at the end of an academic text where you include extra information that doesn’t fit into the main text. The plural of appendix is “appendices.”

In an APA Style paper, appendices are placed at the very end, after the reference list .

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Table of contents

Do i need an appendix, appendix format example, organizing and labeling your appendices, frequently asked questions.

You don’t always need to include any appendices. An appendix should present information that supplements the reader’s understanding of your research but is not essential to the argument of your paper . Essential information is included in the main text.

For example, you might include some of the following in an appendix:

• Full transcripts of interviews you conducted (which you can quote from in the main text)
• Documents used in your research, such as questionnaires , instructions, tests, or scales
• Detailed statistical data (often presented in tables or figures )
• Detailed descriptions of equipment used

You should refer to each appendix at least once in the main text. If you don’t refer to any information from an appendix, it should not be included.

When you discuss information that can be found in an appendix, state this the first time you refer to it:

Note that, if you refer to the same interviews again, it’s not necessary to mention the appendix each time.

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The appendix label appears at the top of the page, bold and centered. On the next line, include a descriptive title, also bold and centered.

The text is presented in general APA format : left-aligned, double-spaced, and with page numbers in the top right corner. Start a new page for each new appendix.

The example image below shows how to format an APA Style appendix.

If you include just one appendix, it is simply called “Appendix” and referred to as such in-text:

When more than one appendix is included, they are labeled “Appendix A,” “Appendix B,” and so on.

Present and label your appendices in the order they are referred to in the main text.

Labeling tables and figures in appendices

An appendix may include (or consist entirely of) tables and/or figures . Present these according to the same formatting rules as in the main text.

Tables and figures included in appendices are labeled differently, however. Use the appendix’s letter in addition to a number. Tables and figures are still numbered separately and according to the order they’re referred to in the appendix.

For example, in Appendix A, your tables are Table A1, Table A2, etc; your figures are Figure A1, Figure A2, etc.

The numbering restarts with each appendix: For example, the first table in Appendix B is Table B1; the first figure in Appendix C is Figure C1; and so on. If you only have one appendix, use A1, A2, etc.

If you want to refer specifically to a table or figure from an appendix in the main text, use the table or figure’s label (e.g. “see Table A3”).

If an appendix consists entirely of a single table or figure, simply use the appendix label to refer to the table or figure. For example, if Appendix C is just a table, refer to the table as “Appendix C,” and don’t add an additional label or title for the table itself.

An appendix contains information that supplements the reader’s understanding of your research but is not essential to it. For example:

• Interview transcripts
• Questionnaires
• Detailed descriptions of equipment

Something is only worth including as an appendix if you refer to information from it at some point in the text (e.g. quoting from an interview transcript). If you don’t, it should probably be removed.

Appendices in an APA Style paper appear right at the end, after the reference list and after your tables and figures if you’ve also included these at the end.

When you include more than one appendix in an APA Style paper , they should be labeled “Appendix A,” “Appendix B,” and so on.

When you only include a single appendix, it is simply called “Appendix” and referred to as such in the main text.

Yes, if relevant you can and should include APA in-text citations in your appendices . Use author-date citations as you do in the main text.

Any sources cited in your appendices should appear in your reference list . Do not create a separate reference list for your appendices.

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Footnotes & Appendices 

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APA style offers writers footnotes and appendices as spaces where additional, relevant information might be shared within a document; this resource offers a quick overview of format and content concerns for these segments of a document. Should additional clarification be necessary, it is always recommended that writers reach out to the individual overseeing their work (i.e., instructor, editor, etc.). For your convenience, a student sample paper is included below; please note the document is filled with  Lorem Ipsum  placeholder text and references to footnotes and appendices are highighlighted. Additional marginal notes also further explain specific portions of the example. 

Footnotes 

Footnotes are supplementary details printed at the bottom of the page pertaining to a paper’s content or copyright information. This supporting text can be utilized in any type of APA paper to support the body paragraphs.

Content-Based Footnotes

Utilizing footnotes to provide supplementary detail can enrich the body text and reinforce the main argument of the paper. Footnotes may also direct readers to an alternate source for more detail on a topic. Though content footnotes can be useful in providing additional context, it is detrimental to include tangential or convoluted information. Footnotes should detail a focused subject; lengthier sections of text are better suited for the body paragraphs.

Acknowledging Copyright

When citing long quotations, images, tables, data, or commercially published questionnaires in-text, it is important to credit the copyright information in a footnote. Functioning much like an in-text citation, a footnote copyright attribution provides credit to the original source and must also be included in a reference list. A copyright citation is needed for both direct reprinting as well as adaptations of content, and these may require express permission from the copyright owner.

Formatting Footnotes

Each footnote and its corresponding in-text callout should be formatted in numerical order of appearance utilizing superscript. As demonstrated in the example below, the superscripted numerals should follow all punctuation with the exception of dashes and parentheses.

For example: 

Footnote callouts should not be placed in headings and do not require a space between the callout and superscripted number. When reintroducing a footnote that has previously been called out, refrain from replicating the callout or footnote itself; rather, format such reference as “see Footnote 4”, for example. Footnotes should be placed at the bottom of the page on which the corresponding callout is referenced. Alternatively, a footnotes page could be created to follow the reference page. When formatting footnotes in the latter manner, center and bold the label “Footnotes” then record each footnote as a double-spaced and indented paragraph. Place the corresponding superscripted number in front of each footnote and separate the numeral from the following text with a single space.

Formatting Copyright Information

To provide credit for images, tables, or figures pulled from an outside source, include the accreditation statement at the end of the note for the visual. Copyright acknowledgements for long quotations or questionnaires should simply be placed in a footnote at the bottom of the page.

When formatting a copyright accreditation, utilize the following format:

• Establish if the content was reprinted or adapted by using language such as “from” for directly copied material or “adapted from” for material that has been modified
• Include the content’s title, author, year of publication, and source
• Cite the copyright holder and year of copyright or indicate that the source is public domain or licensed under Creative Commons
• If express permission was required to reprint the material, include a statement indicating that permission was acquired

Appendices 

When introducing supplementary content that may not fit within the body of a paper, an appendix can be included to help readers better understand the material without distracting from the text itself. Primarily used to introduce research materials, specific details of a study, or participant demographics, appendices are generally concise and only incorporate relevant content. Much like with footnotes, appendices may require an acknowledgement of copyright and, if data is cited, an adherence to the privacy policies that protect participant identities.

Formatting Appendices

An appendix should be created on its own individual page labelled “Appendix” and followed by a title on the next line that describes the subject of the appendix. These headings should be centered and bolded at the top of the page and written in title case. If there are multiple appendices, each should be labelled with a capital letter and referenced in-text by its specific title (for example, “see Appendix B”). All appendices should follow references, footnotes, and any tables or figures included at the end of the document.

Text Appendices 

Appendices should be formatted in traditional paragraph style and may incorporate text, figures, tables, equations, or footnotes. In an appendix, all figures, tables, and other visuals should be labelled with the letter of the corresponding appendix followed by a number indicating the order in which each appears. For example, a table labelled “Table B1” would be the first table in Appendix B. If there is only one appendix in the document, the visuals should still be labelled with the letter A and a number to differentiate them from those contained in the paper itself (for example, “Figure A3” is the third figure in the singular appendix, which is not labelled with a letter in the heading). 

Table or Figure Appendices 

When an appendix solely contains a table or figure, the title of the figure or table should be substituted with the title of the appendix. For example, if Appendix B only includes a figure, the figure should be labelled “Appendix B” rather than “Figure B1”, as it would be named if there were multiple figures included.

If an appendix does not contain text but includes numerous figures or table, the appendix should be formatted like a text appendix. The appendix would receive a name and label, and each figure or table would be given a corresponding letter and number. For example, if Appendix C contains two tables and one figure, these visuals would be labelled “Table C1”, “Table C2”, and “Figure C1” respectively.

Sample Paper    

Media File: APA 7 - Student Sample Paper (Footnotes & Appendices)

• USC Libraries
• Research Guides

Organizing Your Social Sciences Research Paper

• Purpose of Guide
• Design Flaws to Avoid
• Independent and Dependent Variables
• Glossary of Research Terms
• Reading Research Effectively
• Narrowing a Topic Idea
• Broadening a Topic Idea
• Extending the Timeliness of a Topic Idea
• Academic Writing Style
• Choosing a Title
• Making an Outline
• Paragraph Development
• Research Process Video Series
• Executive Summary
• The C.A.R.S. Model
• Background Information
• The Research Problem/Question
• Theoretical Framework
• Citation Tracking
• Content Alert Services
• Evaluating Sources
• Primary Sources
• Secondary Sources
• Tiertiary Sources
• Scholarly vs. Popular Publications
• Qualitative Methods
• Quantitative Methods
• Insiderness
• Using Non-Textual Elements
• Limitations of the Study
• Common Grammar Mistakes
• Writing Concisely
• Avoiding Plagiarism
• Footnotes or Endnotes?
• Further Readings
• Generative AI and Writing
• USC Libraries Tutorials and Other Guides
• Bibliography

An appendix contains supplementary material that is not an essential part of the text itself but which may be helpful in providing a more comprehensive understanding of the research problem or it is information that is too cumbersome to be included in the body of the paper. A separate appendix should be used for each distinct topic or set of data and always have a title descriptive of its contents.

Tables, Appendices, Footnotes and Endnotes. The Writing Lab and The OWL. Purdue University.

Importance of...

Appendices are always supplementary to the research paper. As such, your study must be able to stand alone without the appendices, and the paper must contain all information including tables, diagrams, and results necessary to understand the research problem. The key point to remember when including an appendix or appendices is that the information is non-essential; if it were removed, the reader would still be able to  comprehend the significance, validity , and implications of your research.

It is appropriate to include appendices for the following reasons:

• Including this material in the body of the paper that would render it poorly structured or interrupt the narrative flow;
• Information is too lengthy and detailed to be easily summarized in the body of the paper;
• Inclusion of helpful, supporting, or useful material would otherwise distract the reader from the main content of the paper;
• Provides relevant information or data that is more easily understood or analyzed in a self-contained section of the paper;
• Can be used when there are constraints placed on the length of your paper; and,
• Provides a place to further demonstrate your understanding of the research problem by giving additional details about a new or innovative method, technical details, or design protocols.

Appendices. Academic Skills Office, University of New England; Chapter 12, "Use of Appendices." In Guide to Effective Grant Writing: How to Write a Successful NIH Grant . Otto O. Yang. (New York: Kluwer Academic, 2005), pp. 55-57; Tables, Appendices, Footnotes and Endnotes. The Writing Lab and The OWL. Purdue University.

Structure and Writing Style

I.  General Points to Consider

When considering whether to include content in an appendix, keep in mind the following:

• It is usually good practice to include your raw data in an appendix, laying it out in a clear format so the reader can re-check your results. Another option if you have a large amount of raw data is to consider placing it online [e.g., on a Google drive] and note that this is the appendix to your research paper.
• Any tables and figures included in the appendix should be numbered as a separate sequence from the main paper . Remember that appendices contain non-essential information that, if removed, would not diminish a reader's ability to understand the research problem being investigated. This is why non-textual elements should not carry over the sequential numbering of non-textual elements in the body of your paper.
• If you have more than three appendices, consider listing them on a separate page in the table of contents . This will help the reader know what information is included in the appendices. Note that some works list appendices in the table of contents before the first chapter while other styles list the appendices after the conclusion but before your references. Consult with your professor to confirm if there is a preferred approach.
• The appendix can be a good place to put maps, photographs, diagrams, and other images , if you feel that it will help the reader to understand the content of your paper, while keeping in mind the study should be understood without them.
• An appendix should be streamlined and not loaded with a lot information . If you have a very long and complex appendix, it is a good idea to break it down into separate appendices, allowing the reader to find relevant information quickly as the information is covered in the body of the paper.

II.  Content

Never include an appendix that isn’t referred to in the text . All appendices should be summarized in your paper where it is relevant to the content. Appendices should also be arranged sequentially by the order they were first referenced in the text [i.e., Appendix 1 should not refer to text on page eight of your paper and Appendix 2 relate to text on page six].

There are very few rules regarding what type of material can be included in an appendix, but here are some common examples:

• Correspondence -- if your research included collaborations with others or outreach to others, then correspondence in the form of letters, memorandums, or copies of emails from those you interacted with could be included.
• Interview Transcripts -- in qualitative research, interviewing respondents is often used to gather information. The full transcript from an interview is important so the reader can read the entire dialog between researcher and respondent. The interview protocol [list of questions] should also be included.
• Non-textual elements -- as noted above, if there are a lot of non-textual items, such as, figures, tables, maps, charts, photographs, drawings, or graphs, think about highlighting examples in the text of the paper but include the remainder in an appendix.
• Questionnaires or surveys -- this is a common form of data gathering. Always include the survey instrument or questionnaires in an appendix so the reader understands not only the questions asked but the sequence in which they were asked. Include all variations of the instruments as well if different items were sent to different groups [e.g., those given to teachers and those given to administrators] .
• Raw statistical data – this can include any numerical data that is too lengthy to include in charts or tables in its entirety within the text. This is important because the entire source of data should be included even if you are referring to only certain parts of a chart or table in the text of your paper.
• Research instruments -- if you used a camera, or a recorder, or some other device to gather information and it is important for the reader to understand how, when, and/or where that device was used.
• Sample calculations – this can include quantitative research formulas or detailed descriptions of how calculations were used to determine relationships and significance.

NOTE:   Appendices should not be a dumping ground for information. Do not include vague or irrelevant information in an appendix; this additional information will not help the reader’s overall understanding and interpretation of your research and may only distract the reader from understanding the significance of your overall study.

ANOTHER NOTE :   Appendices are intended to provide supplementary information that you have gathered or created; it is not intended to replicate or provide a copy of the work of others. For example, if you need to contrast the techniques of analysis used by other authors with your own method of analysis, summarize that information, and cite to the original work. In this case, a citation to the original work is sufficient enough to lead the reader to where you got the information. You do not need to provide a copy of this in an appendix.

III.  Format

Here are some general guideline on how to format appendices . If needed, consult the writing style guide [e.g., APA, MLS, Chicago] your professor wants you to use for more detail:

• Appendices may precede or follow your list of references.
• Each appendix begins on a new page.
• The order they are presented is dictated by the order they are mentioned in the text of your research paper.
• The heading should be "Appendix," followed by a letter or number [e.g., "Appendix A" or "Appendix 1"], centered and written in bold type.
• If there is a table of contents, the appendices must be listed.
• The page number(s) of the appendix/appendices will continue on with the numbering from the last page of the text.

Appendices. The Structure, Format, Content, and Style of a Journal-Style Scientific Paper. Department of Biology. Bates College;  Appendices. Academic Skills Office, University of New England; Appendices. Writing Center, Walden University; Chapter 12, "Use of Appendices." In Guide to Effective Grant Writing: How to Write a Successful NIH Grant . Otto O. Yang. (New York: Kluwer Academic, 2005), pp. 55-57 ; Tables, Appendices, Footnotes and Endnotes. The Writing Lab and The OWL. Purdue University; Lunsford, Andrea A. and Robert Connors. The St. Martin's Handbook . New York: St. Martin's Press, 1989; What To Know About The Purpose And Format Of A Research Paper Appendix. LoyolaCollegeCulion.com.

Writing Tip

Consider Putting Your Appendices Online

Appendices are useful because they provide the reader with information that supports your study without breaking up the narrative or distracting from the main purpose of your paper. If you have a lot of raw data or information that is difficult to present in textual form, consider uploading it to an online site. This prevents your paper from having a large and unwieldy set of appendices and it supports a growing movement within academe to make data more freely available for re-analysis. If you do create an online portal to your data, note it prominently in your paper with the correct URL and access procedures if it is a secured site.

Piwowar, Heather A., Roger S. Day, and Douglas B. Fridsma. “Sharing Detailed Research Data Is Associated with Increased Citation Rate.” PloS ONE (March 21, 2007); Wicherts, Jelte M., Marjan Bakker, and Dylan Molenaar. “Willingness to Share Research Data Is Related to the Strength of the Evidence and the Quality of Reporting of Statistical Results.” PLoS ONE (November 2, 2011).

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APA 7th edition - Paper Format: Appendices

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How to Format An Appendix - Tutorial

• APA Appendices - JIBC Tip Sheet All you need to know about appendices in APA Style.

Information in this section is as outlined in the APA Publication Manual (2020), sections 2.14, 2.17, 2.24, and 7.6.

Appendices are used to include information that supplement the paper’s content but are considered distracting or inappropriate for the overall topic. It is recommended to only include an appendix if it helps the reader comprehend the study or theoretical argument being made. It is best if the material included is brief and easily presented. The material can be text, tables, figures, or a combination of these three.

Placement :

Appendices should be placed on a separate page at the end of your paper after the references, footnotes, tables, and figure. The label and title should be centre aligned. The contents of the appendix and the note should be left-aligned.

• If you are choosing to include tables and figures in your appendix, then you can list each one on a separate page or you may include multiple tables/figures in one appendix, if there is no text and each table and/or figure has its own clear number and title within the appendix.
• Tables and figures in an appendix receive a number preceded by the letter of the appendix in which it appears, e.g. Table A1 is the first table in Appendix A or of a sole appendix that is not labeled with a letter.

The follow elements are required for appendices in APA Style:

Appendix Labels:

Each appendix that you place in your paper is labelled “Appendix.” If a paper has more than one appendix, then label each with a capital letter in the order the appendices are referred to in your paper (“Appendix A” is referred to first, “Appendix B” is referred to second, etc).

• The label of the appendix should be in bold font, centre-aligned, follow Title Casing, and is located at the top of the page.
• If your appendix only contains one table or figure (and no text), then the appendix label takes the place of the table/figure number, e.g. the table may be referred to as “Appendix B” rather than “Table B1.”

Appendix Titles:

Each appendix should have a title, that describes its contents. Titles should be brief, clear, and explanatory.

• The title of the appendix should be in bold font, centre-aligned, follow Title Casing, and is one double-spaced line down from the appendix label.
• If your appendix only contains one table or figure (and no text), then the appendix title takes the place of the table/figure title. 

Appendix Contents:

• Left aligned and indented; written the same as paragraphs within the body of the paper
• Double-spaced and with the same font as the rest of the paper
• If the appendix contains a table and/or figure, then the table/figure number must contain a letter to correlate the table and/or figure to the appendix and not the body of the paper, e.g. “Table A1” rather than “Table 1” to clarify that the table appears in the appendix and not in the body of the paper.
• All tables and figures in an appendix must be mentioned in the appendix and numbered in order of mention. 
• All tables and figures must be aligned to the left margin, (not center aligned), and positioned after a paragraph break, preferably the paragraph in which they are referred to, with a double-spaced blank line between the table and the text. 
• Each table and figure should include a note afterwards to further explain the supplement or clarify information in the table or figure to your paper/appendix and can be general, specific, and probability. See “Table Notes” in the section “Table and Figures” above for more details.

Referring to Appendices in the Text:

In your paper, refer to every appendix that you have inserted. Do not include an appendix in your work that you do not clearly explain in relation to the ideas in your paper.

• In general, only refer to the appendix by the label (“Appendix” or “Appendix A” etc.) and not the appendix title.

Reprinting or Adapting:

If you did not create the content in the appendix yourself, for instance if you found a figure on the internet, you must include a copyright attribution in a note below the figure. 

• A copyright attribution is used instead of an in-text citation. 
• Each work should also be listed in the reference list. 

Please see pages 390-391 in the Manual for example copyright attributions.

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Home » Appendices – Writing Guide, Types and Examples

Appendices – Writing Guide, Types and Examples

Table of Contents

Definition:

Appendices refer to supplementary materials or documents that are attached to the end of a Book, Report , Research Paper , Thesis or other written work. These materials can include charts, graphs, tables, images, or other data that support the main content of the work.

Types of Appendices

Types of appendices that can be used depending on the content and purpose of the document. These types of Appendices are as follows:

Statistical Appendices

Statistical appendices are used to present raw data or statistical analysis that is relevant to the main text but would be too bulky to include in the main body of the document. These appendices may include tables, graphs, charts, or other types of visual aids that help to illustrate the data.

Technical Appendices

Technical appendices are used to provide detailed technical information that is relevant to the main text but would be too complex or lengthy to include in the main body of the document. These appendices may include equations, formulas, diagrams, or other technical details that are important for understanding the subject matter.

Bibliographical Appendices

Bibliographical appendices are used to provide additional references or sources that are relevant to the main text but were not cited in the main body of the document. These appendices may include lists of books, articles, or other resources that the author consulted in the course of their research.

Historical Appendices

Historical appendices are used to provide background information or historical context that is relevant to the main text but would be too lengthy or distracting to include in the main body of the document. These appendices may include timelines, maps, biographical sketches, or other historical details that help to contextualize the subject matter.

Supplemental Appendices

Supplemental appendices are used to provide additional material that is relevant to the main text but does not fit into any of the other categories. These appendices may include interviews, surveys, case studies, or other types of supplemental material that help to further illustrate the subject matter.

Applications of Appendices

Some applications of appendices are:

• Providing detailed data and statistics: Appendices are often used to include detailed data and statistics that support the findings presented in the main body of the document. For example, in a research paper, an appendix might include raw data tables or graphs that were used to support the study’s conclusions.
• Including technical details: Appendices can be used to include technical details that may be of interest to a specialized audience. For example, in a technical report, an appendix might include detailed calculations or equations that were used to develop the report’s recommendations.
• Presenting supplementary information: Appendices can be used to present supplementary information that is related to the main content but doesn’t fit well within the main body of the document. For example, in a business proposal, an appendix might include a list of references or a glossary of terms.
• Providing supporting documentation: Appendices can be used to provide supporting documentation that is required by the document’s audience. For example, in a legal document, an appendix might include copies of contracts or agreements that were referenced in the main body of the document.
• Including multimedia materials : Appendices can be used to include multimedia materials that supplement the main content. For example, in a book, an appendix might include photographs, maps, or illustrations that help to clarify the text.

Importance of Appendices

Appendices are important components of research papers, reports, Thesis, and other academic papers. They are supplementary materials that provide additional information and data that support the main text. Here are some reasons why appendices are important:

• Additional Information : Appendices provide additional information that is too detailed or too lengthy to include in the main text. This information includes raw data, graphs, tables, and charts that support the research findings.
• Clarity and Conciseness : Appendices help to maintain the clarity and conciseness of the main text. By placing detailed information and data in appendices, writers can avoid cluttering the main text with lengthy descriptions and technical details.
• Transparency : Appendices increase the transparency of research by providing readers with access to the data and information used in the research process. This transparency increases the credibility of the research and allows readers to verify the findings.
• Accessibility : Appendices make it easier for readers to access the data and information that supports the research. This is particularly important in cases where readers want to replicate the research or use the data for their own research.
• Compliance : Appendices can be used to comply with specific requirements of the research project or institution. For example, some institutions may require researchers to include certain types of data or information in the appendices.

Appendices Structure

Here is an outline of a typical structure for an appendix:

I. Introduction

• A. Explanation of the purpose of the appendix
• B. Brief overview of the contents

II. Main Body

• A. Section headings or subheadings for different types of content
• B. Detailed descriptions, tables, charts, graphs, or images that support the main content
• C. Labels and captions for each item to help readers navigate and understand the content

III. Conclusion

• A. Summary of the key points covered in the appendix
• B. Suggestions for further reading or resources

IV. Appendices

• A. List of all the appendices included in the document
• B. Table of contents for the appendices

V. References

• A. List of all the sources cited in the appendix
• B. Proper citation format for each source

Example of Appendices

here’s an example of what appendices might look like for a survey:

Appendix A:

Survey Questionnaire

This section contains a copy of the survey questionnaire used for the study.

• What is your age?
• What is your gender?
• What is your highest level of education?
• How often do you use social media?
• Which social media platforms do you use most frequently?
• How much time do you typically spend on social media each day?
• Do you feel that social media has had a positive or negative impact on your life?
• Have you ever experienced cyberbullying or harassment on social media?
• Have you ever been influenced by social media to make a purchase or try a new product?
• In your opinion, what are the biggest advantages and disadvantages of social media?

Appendix B:

Participant Demographics

This section includes a table with demographic information about the survey participants, such as age, gender, and education level.

Age Gender Education Level

• 20 Female Bachelor’s Degree
• 32 Male Master’s Degree
• 45 Female High School Diploma
• 28 Non-binary Associate’s Degree

Appendix C:

Statistical Analysis

This section provides details about the statistical analysis performed on the survey data, including tables or graphs that illustrate the results of the analysis.

Table 1: Frequency of Social Media Platforms

Use Platform Frequency

• Facebook 35%
• Instagram 28%
• Twitter 15%
• Snapchat 12%

Figure 1: Impact of Social Media on Life Satisfaction

Appendix D:

Survey Results

This section presents the raw data collected from the survey, such as participant responses to each question.

Question 1: What is your age?

Question 2: What is your gender?

And so on for each question in the survey.

How to Write Appendices

Here are the steps to follow to write appendices:

• Determine what information to include: Before you start writing your appendices, decide what information you want to include. This may include tables, figures, graphs, charts, photographs, or other types of data that support the main content of your paper.
• Organize the material: Once you have decided what to include, organize the material in a logical manner that follows the sequence of the main content. Use clear headings and subheadings to make it easy for readers to navigate through the appendices.
• Label the appendices: Label each appendix with a capital letter (e.g., “Appendix A,” “Appendix B,” etc.) and provide a brief descriptive title that summarizes the content.
• F ormat the appendices: Follow the same formatting style as the rest of your paper or report. Use the same font, margins, and spacing to maintain consistency.
• Provide detailed explanations: Make sure to provide detailed explanations of any data, charts, graphs, or other information included in the appendices so that readers can understand the significance of the material.
• Cross-reference the appendices: In the main text, cross-reference the appendices where appropriate by referring to the appendix letter and title (e.g., “see Appendix A for more information”).
• Review and revise: Review and revise the appendices just as you would any other part of your paper or report to ensure that the information is accurate, clear, and relevant.

When to Write Appendices

Appendices are typically included in a document when additional information needs to be provided that is not essential to the main text, but still useful for readers who want to delve deeper into a topic. Here are some common situations where you might want to include appendices:

• Supporting data: If you have a lot of data that you want to include in your document, but it would make the main text too lengthy or confusing, you can include it in an appendix. This is especially useful for academic papers or reports.
• Additional examples: I f you want to include additional examples or case studies to support your argument or research, but they are not essential to the main text, you can include them in an appendix.
• Technical details: I f your document contains technical information that may be difficult for some readers to understand, you can include detailed explanations or diagrams in an appendix.
• Background information : If you want to provide background information on a topic that is not directly related to the main text, but may be helpful for readers, you can include it in an appendix.

Purpose of Appendices

The purposes of appendices include:

• Providing additional details: Appendices can be used to provide additional information that is too detailed or bulky to include in the main body of the document. For example, technical specifications, data tables, or lengthy survey results.
• Supporting evidence: Appendices can be used to provide supporting evidence for the arguments or claims made in the main body of the document. This can include supplementary graphs, charts, or other visual aids that help to clarify or support the text.
• Including legal documents: Appendices can be used to include legal documents that are referred to in the main body of the document, such as contracts, leases, or patent applications.
• Providing additional context: Appendices can be used to provide additional context or background information that is relevant to the main body of the document. For example, historical or cultural information, or a glossary of technical terms.
• Facilitating replication: In research papers, appendices are used to provide detailed information about the research methodology, raw data, or analysis procedures to facilitate replication of the study.

Advantages of Appendices

Some Advantages of Appendices are as follows:

• Saving Space: Including lengthy or detailed information in the main text of a document can make it appear cluttered and overwhelming. By placing this information in an appendix, it can be included without taking up valuable space in the main text.
• Convenience: Appendices can be used to provide supplementary information that is not essential to the main argument or discussion but may be of interest to some readers. By including this information in an appendix, readers can choose to read it or skip it, depending on their needs and interests.
• Organization: Appendices can be used to organize and present complex information in a clear and logical manner. This can make it easier for readers to understand and follow the main argument or discussion of the document.
• Compliance : In some cases, appendices may be required to comply with specific document formatting or regulatory requirements. For example, research papers may require appendices to provide detailed information on research methodology, data analysis, or technical procedures.

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• How To Write A Research Paper Appendix: A Step-by-Step Guide

Think of appendices like bonus levels on your favorite video game. They are not a major part of the game, but they boost your points and they make the game worthwhile. 

Appendix are important facts, calculations, or data that don’t fit into the main body of your research paper. Having an appendix gives your research paper more details, making it easier for your readers to understand your main ideas.

Let’s dive into how to create an appendix and its best practices.

Understanding the Purpose of an Appendix

If you’re looking to add some extra depth to your research, appendices are a great way to do it.  They allow you to include extremely useful information that doesn’t fit neatly into the main body of your research paper, such as huge raw data, multiple charts, or very long explanations.

Think of your appendix as a treasure chest with different compartments. You can include different information including, extra data, surveys, graphs, or even detailed explanations of your methods. You can fit anything too big or detailed for the main paper in the appendix.

Planning Your Appendix

Before you dive into making your appendix, it’s a good idea to plan things out; think of it as drawing a map before going on an adventure. 

You want your appendix to be organized and provide more context to your research. Not planning it will make the process time-consuming and make the appendix confusing to people reading your research paper.

How to Decide What to Include in Your Research Paper

You have to sort through the content that you will include in your appendix. Think of what your readers need to know to understand your key points. Anything that’s overly detailed, off-topic, or clutters up your paper is a good candidate for your appendix.

Tips for Organizing Your Appendix

Once you’ve figured out what to put in your appendix, it’s time to organize it. Your appendix is a place to add extra information, but it shouldn’t be cluttered or confusing to your readers. Instead, it should make your research paper easier to understand.

Use clear headings, labels, and even page numbers to help your readers find the information they need in the appendix. This way, it’s not a jumbled mess, but a well-organized part of your research paper

Formatting Guidelines

Yes, your appendix must be formatted. Most of the time, you’ll want to keep the font and margin sizes consistent with your main paper. 

However, some universities and journals may have specific guidelines for appendix formatting. Verify if your institution has special guidelines, if they do, follow them, if they don’t use the same format as your main text.

Here’s a typical breakdown of how to format your appendix:

(1) Labeling and Titling 

If you have different types of information in your appendix, use letters to label them, such as “Appendix A” and “Appendix B”. Then, give each appendix a title that explains the information inside it. 

For example, if the first section of your appendix contains raw survey data, you could call it “Appendix A (Survey Data of People Living with Diabetes Under 18 in Texas)”. If the second section of your appendix contains charts, you could call it “Appendix B (The Effect of Sugar Tax in Curbing Diabetes in Children and Young Adults)”.

(2) Numbering Tables, Figures, and More 

If you have tables, figures, or other things in your appendix, number them like a list. For example, “Table A1,” “Figure A1,” and more. This numbering helps your readers know what they’re looking at, sort of like chapters in a book.

Creating Tables and Figures

Using tables and figures helps you organize your data neatly in your appendix. Here’s a step-by-step guide to creating tables and figures in your appendix:

Choose the Right Format for Your Appendix Data

Before creating tables or figures, you need to pick the right format to display the information. Think about what makes your data most clear and understandable. 

For example, a table is better for detailed numbers, while a graph is great for showing trends. The right format makes your information easy to grasp and makes your paper look organized.

How to Create Tables in Your Appendix

You can use a spreadsheet program (like Excel or Google Sheets) to create tables to arrange information neatly. Make sure to give your table a clear title so readers know what it’s about.

Here’s a step-by-step guide to creating tables with a spreadsheet program:

• Open Google Sheets/Excel : Access Google Sheets or Excel through the web or download the app
• Open a New Spreadsheet or Existing File : Create a new spreadsheet or open an existing one where you want to insert a table.
• Select Data : Click and drag to select the data you want to include in the table.
• Insert Table : Once your data is selected, go to the “Insert” menu, then select “Table.
• Create Table : A dialog box will appear, confirming the selected data range. Make sure the “Use the first row as headers” option is checked if your data has headers. Click “Insert .”
• Customize Your Table : After inserting the table, you can customize it by adjusting the style, format, and other table properties using the “Table” menu in Google Sheets or Excel.

You can use software like PowerPoint, Google Slides, or graphic design tools to create them. If you have a chart or graph, make sure it’s easy to understand and add a title or labels to explain it. 

You can use the editing tools for images to change the size and other aspects of the image.

Stop Struggling with Research Proposals! Get Organized and Impress Reviewers with our Template

Including Raw Data

The major reasons for including raw data in your appendix are transparency and credibility. Raw data is like your research recipe; it shows exactly what you worked with to arrive at your conclusions.

Raw data also provides enough information to guide researchers in replicating your study or getting a deeper understanding of your research.

Formatting and Presenting Raw Data 

Formatting your raw data makes it easy for anyone to understand. You can use tables, charts, or even lists to display your data. For example, if you did a survey, you could put the survey responses in a table with clear headings.

When presenting your raw data, clear organization is your best friend. Use headings, labels, and consistent formatting to help your readers find and understand the data. This keeps your appendix from becoming a confusing puzzle.

Citing Your Appendix

Referencing your appendix in the main text gives readers a full picture of your research while they’re reading- They don’t have to wait until the end to figure out important details of your research.

Unlike actual references and citations, citing your appendix is a very straightforward process. You can simply say, “See Appendix A for more details.”

In-Text Citations for Appendix Content

If you would like to cite information in your appendix, you usually mention the author, year, and what exactly you’re citing. This allows you to give credit to the original creator of the content, so your readers know where it came from.

For instance, if you included a chart from a book in your appendix, you’d say something like (Author, Year, p. X). Keep in mind that there are different citation styles (APA, MLA, Chicago, and others), so your appendix may look a little different.

Proofreading and Editing

Proofreading and editing your appendix is just as important as proofreading and editing the main body of your paper. A poorly written or formatted appendix can leave a negative impression on your reader and detract from the overall quality of your work. 

Make sure that your appendix is consistent with the main text of your paper in terms of style and tone unless otherwise stated by your institution. Use the same font, font size, and line spacing in the appendix as you do in the main body of your paper. 

Your appendix should also be free of errors in grammar, spelling, punctuation, and formatting.

Tips for Checking for Errors in Formatting, Labeling, and Content

Here are some tips for checking for errors in formatting, labeling, and content in your appendix:

• Formatting : Make sure that all of the elements in your appendix are formatted correctly, including tables, figures, and equations. Check the margins, line spacing, and font size to make sure that they are consistent with the rest of your paper.
• Labeling : All of the tables, figures, and equations in your appendix should be labeled clearly and consistently. Use a consistent numbering system and make sure that the labels match the references in the main body of your paper.
• Content : Proofread your appendix carefully to catch any errors in grammar, spelling, punctuation, and content. You can use grammar editing tools such as Grammarly to help you automatically detect errors in your context.

Appendix Checklist

Having an appendix checklist guarantees a well-organized appendix and helps you spot and correct any overlooked mistakes.

Here’s a checklist of key points to review before finalizing your appendix:

• Is all of the information in the appendix relevant and necessary?
• Is the appendix well-organized and easy to understand?
• Are all the tables, numbers, and equations clearly labeled?
• Is the appendix formatted correctly and consistently with the main body of the paper?
• Is the appendix free of errors in grammar, spelling, punctuation, and content?

Sample Appendix

We have discussed what you should include in your appendix and how to organize it. Let’s take a look at what a well-formatted appendix looks like:

Appendix A. (Raw Data of Class Scores)

The following table shows the raw data collected for the study.

How the Sample Appendix Adheres to Best Practices

• The appendix is labeled clearly and concisely as “Appendix A. (Raw Data of Class Score).”
• The appendix begins on a new page.
• The appendix is formatted consistently with the rest of the paper, using the same font, font size, and line spacing.
• The table in the appendix is labeled clearly and concisely as “Table A1.”
• The table is formatted correctly, with consistent column widths and alignment.
• The table includes all of the necessary information, including the participant number, age, gender, and score.
• The appendix is free of grammar, spelling, and punctuation errors.

Having an appendix easily makes your research paper impressive to reviewers, and increases your likelihood of achieving high grades or journal publication.  It also makes it easier for other researchers to replicate your research, allowing you to make a significant contribution to your research field.

Ensure to use the best practices in this guide to create a well-structured and relevant appendix. Also, use the checklist provided in this article to help you carefully review your appendix before submitting it.

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Reference management. Clean and simple.

What is an appendix in a paper

What is an appendix?

What type of information includes an appendix, the format of an appendix, frequently asked questions about appendices in papers, related articles.

An appendix is a section of a paper that features supporting information not included in the main text.

The appendix of a paper consists of supporting information for the research that is not necessary to include in the text. This section provides further insight into the topic of research but happens to be too complex or too broad to add to the body of the paper. A paper can have more than one appendix, as it is recommended to divide them according to topic.

➡️ Read more about  what is a research paper?

An appendix can take many types of forms. Here are some examples:

• Surveys. Since many researchers base their methodology on surveys, these are commonly found attached as appendices. Surveys must be included exactly as they were presented to the respondents, and exactly how they were answered so the reader can get a real picture of the findings.
• Interviews . Whether it’s a transcript or a recording, interviews are usually included as an appendix. The list of questions and the real answers must be presented for complete transparency.
• Correspondence . All types of communication with collaborators regarding the research should be included as an appendix. These can be emails, text messages, letters, transcripts of audio messages, etc.
• Research tools . Any instrument used to perform the research should be acknowledged in an appendix to give the reader insight into the process. For instance, audio recorders, cameras, special software, etc.
• Non-textual items . If the research includes too many graphs, tables, figures, illustrations, photos or charts, these should be added as an appendix.
• Statistical data . When raw data is too long, it should be attached to the research as an appendix. Even if only one part of the data was used, the complete data must be given.

➡️ Learn more about surveys, interviews, and other research methodologies .

The format of an appendix will vary based on the type of citation style you’re using, as well as the guidelines of the journal or class for which the paper is being written. Here are some general appendix formatting rules:

• Appendices should be divided by topic or by set of data.
• Appendices are included in the table of contents.

The most common heading for an appendix is Appendix A or 1, centered, in bold, followed by a title describing its content.

• An appendix should be located before or after the list of references.
• Each appendix should start on a new page.
• Each page includes a page number.
• Appendices follow a sequential order, meaning they appear in the order in which they are referred to throughout the paper.

An appendix is usually added before or after the list of references.

There is no specific space limit to an appendix, but make sure to consult the guidelines of the citation format you are using.

Yes, all appendices must be included in the table of contents.

Appendices feature different types of material, for instance interviews, research tools, surveys, raw statistical data, etc.

Use an Appendix or Annex in Your Research Paper?

'Appendix' and 'annex' are commonly confused in research papers. While the use of an appendix is more common, the annex can also be a valuable way of supplementing your research. The appendix and the annex add supporting/supplementary information. Both are posted online and can be referred to by researchers with a particular interest in your study. The differences between them are context and length.

Updated on July 26, 2022

The terms “appendix” and “annex” are commonly confused in research papers. While the use of an appendix is more common, the annex can also be a valuable way of supplementing your research.

Both the appendix and the annex add supporting/supplementary information (SI), like tables and graphs, datasets, or transcriptions. Both are posted online and can be referred to by researchers with a particular interest in your study (especially if they're open access).

The main differences between these two forms of data supplement are context and length. Appendixes are common and are part of the study; you likely used them in theses and dissertations. Annexes deal with much longer and more detailed sets of information, and they're additional to the study's content. Let's take a deeper look at the differences so you'll never them confused.

What is an appendix?

An appendix is, according to Merriem-Webster, “supplementary material usually attached at the end of a piece of writing.” The word comes from the Latin appendere, which means “cause to hang (from something).” It's included in the paper at the end, usually after the references or bibliography.

Appendixes/Appendices can be seen as materials that supplement rather than complement the research. Read only by those with a specific interest.

Basics of an appendix

The following are generally true of an appendix.

• Included at the end of the manuscript.
• Written by one more of the paper's researchers. Exceptions are items like letters granting ethical clearance for the research or details of the research tools used (see the example later).
• Ties into the research directly; gives greater detail than the main body of the manuscript.
• Not too long. Of course, that's subjective, but generally speaking, it's a page or two rather than dozens of pages, or more.

What to put in an appendix

Some examples of an appendix are:

• Figures and tables
• Photographs
• Raw data (tables, plots, images)
• Questionnaires and interview questions (especially in qualitative research)
• Ethics approvals such as from the IRB
• Correspondences, such as letters or emails

Most research published as a journal article, and particularly as a thesis, will contain appendices rather than annexes.

This paper (PDF link) includes an appendix that details the instruments used in the research. Each test was used in the study, and the author felt the details were important enough to detail in the appendix, too much information to be presented in the main paper.

This chemistry article also presents supplementary data in the appendix. As it's too lengthy to put in print, a downloadable Word file is available. However, it's only data rather than an article or other full and standalone materials, which is likely why it was made into an appendix rather than an annex.

What is an annex?

Merriam-Webster defines an annex as “an added stipulation or statement.” In the context of research, both academic and commercial, annexes are usually separate additions to the research output and are submitted as separate documents.

Annex comes from the French annexer, which means “to join or attach.” Simply put, an annex comes along with (joining or attached to) a research paper. An example might be a UN report relevant to a manuscript, and that will be added as a supporting document, backing up the research findings. Annexes are used for materials that complement the research.

Basics of an annex

• Attached to the research paper as a separate item.
• Often (but not always) produced by someone outside the research team. If, for example, one of the researchers produced a white paper for the government on the research domain and this might complement the research, this could be an annex.
• Can be many pages long.
• Supports or informs the research that has been done; complements it.
• Is not part of the research output presented in the manuscript's body text.

What to put in an annex

Some examples of an annex are...

• Documents mentioned in the manuscript or that may support the manuscript
• News articles
• Lab reports
• Interviews of people mentioned in the manuscript.
• Data from other studies

Almost always, annexes are added to papers that exceed normal journal article lengths. They're supporting materials to lengthy research output, like those often funded by corporate or government funding.

This World Health Organization guidance paper on HIV/AIDS is itself 21 pages long but comes with separate downloadable annexes. The paper details the findings stemming from the research and describes the processes for the trials. On page 5, the paper notes that the annexes are included to give greater details on the clinical trials mentioned in the paper. In this sense, the annexes are for readers who want greater detail.

The paper reviews the trials done in the annex, but because the trials were not part of the research and was done by others, it was added as an annex.

Should you use an appendix or an annex?

Short answer: you should probably use an appendix. That's because they're much more common. Appendices are placed at the end of a document, while annexes are, technically, separate from it. The former is part of the paper, but the latter is not.

Annexes are often long documents, running even to hundreds of pages. Most often, someone an annex's author is someone who's not part of the research team. Appendices, however, are often by a paper's author(s) and are usually not more than a few pages each (though, in the case of datasets, they technically can be quite long).

Annexes are used to verify the research and provide additional, relevant information. They are documents from credible and relevant sources. They offer further insight into the research topic.

Normally, you'll be using appendices, and that's often because of the journal's word count limits. It may be ideal to include tables or charts in-line in the article, but if there's no room, the appendix can provide extra space.

Handling data: A workflow for dealing with data in your SI

Submission and sharing of data are especially key steps in dealing with your SI in appendixes, annexes, and other formats. When you're submitting your article to a journal, there is a common workflow for this:

• Create additional supplementary files (usually as few as possible, a single file is ideal).
• Upload to the journal site or one of the many ‘approved' online data repositories.
• You'll be given a URL to link back to your data files.
• Add this link to the Acknowledgements section of your paper with some text such as “Additional files in support of this article can be found at https://...”

Some commonly used and ostensibly approved online data repositories:

• Harvard Dataverse
• Open Science Framework (OSF)
• Mendeley Data

But don't get carried away!

Supplementary information, including appendixes and annexes, can also be abused. Additional information may be so long/big/dense that it actually may not undergo full peer review even though the rest of the article does.

A study by Pop and Salzberg asserted that journals' word restrictions may cause authors to move key information outside the main manuscript body. In this way, it can avert proper peer review while also being less accessible to the reader. This hinders further investigation because readers have to wade through huge amounts of supplementary documents to find what they're after.

It also robs authors cited in the supplementary information of the recognition they would receive from citations in the body text.

Nature commendably lays out specifics for SI – check them here .

Final thoughts

If you're unsure of what needs to be in your supplementary information, or if you even need an appendix or annex, as well as the English quality and style, a scientific edit can be a big help. Explore AJE's extensive editing services here .

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How To Use Appendices in Research Papers

Posted by Rene Tetzner | Apr 11, 2021 | Referencing & Bibliographies | 0 |

How To Use Appendices in Research Papers Scholarly books often make good use of appendices (also called appendixes or annexes) and although it is rarer for appendices to be included in academic and scientific articles, many journal guidelines allow them. An appendix can present subsidiary or supplementary material that is directly related to the main argument in a book or paper and therefore potentially helpful to the reader, but which might prove distracting or inappropriate or simply too space consuming were it included in the main text. Often such material is relegated to footnotes, but if this would result in a footnote (or footnotes) too long and complex to be effective on the page, moving that material to an appendix is a good solution. An appendix is also a good format for material that is mentioned or discussed in more than one place in a long document, for it allows the author to avoid repetition while rendering the necessary information readily available to readers. In all three cases, using an appendix to provide the supporting information will streamline your argument without sacrificing helpful material.

Appendices can contain a wide variety of material, such as texts, translations, chronologies, genealogies, examples of principles and procedures, descriptions of complex pieces of equipment, survey questionnaires, participant responses, detailed demographics for a population or sample, lists (particularly long ones), tables and figures, explanations or elaborations of certain aspects of a study and any other supplementary information relevant to a book or article. However, as the Chicago Manual of Style warns, an ‘appendix should not be a repository for odds and ends that the author could not work into the text’ (2003, p.27). Ideally, each appendix should have a specific theme, focus or function and gather together materials of a particular type or relating to a particular topic. If more than one theme or topic requires this sort of treatment, additional appendices should be preferred to subdividing a single long appendix, although appendices can certainly make use of internal headings and subheadings.

It is best if appendices can stand on their own, so all abbreviations, symbols and specialised or technical terminology should be briefly defined or explained in the appendix itself, enabling the reader to understand the material without recourse to definitions and explanations elsewhere in the document. All information in appendices that overlaps material in the main body of a book or paper should also correspond with that material precisely in both content and format. If only one appendix is used, it can simply be called ‘Appendix,’ but if more than one is included, all appendices should be clearly labelled in an order representative of the order in which they are first mentioned in the main text. Letters or numbers can be used (e.g., ‘Appendix A’ or ‘Appendix 1’), and topic-specific headings can be added as well (Appendix A: Questionnaire 3 in German and English), but each appendix should be clearly referred to by its label when it is discussed in the text. Following these simple procedures will enable your appendices to meet the needs of your readers effectively.

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Organizing Academic Research Papers: Appendices

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An appendix contains supplementary material that is not an essential part of the text itself but which may be helpful in providing a more comprehensive understanding of the research problem and/or is information which is too cumbersome to be included in the body of the paper. A separate appendix should be used for each distinct topic or set of data and always have a title descriptive of its contents .

Importance of...

Your research paper must be complete without the appendices, and it must contain all information including tables, diagrams, and results necessary to address the research problem. The key point to remember when you are writing an appendix is that the information is non-essential; if it were removed, the paper would still be understandable.

It is appropriate to include appendices...

• When the incorporation of material in the body of the work would make it poorly structured or it would be too long and detailed and
• To ensure inclusion of helpful, supporting, or essential material that would otherwise clutter or break up the narrative flow of the paper, or it would be distracting to the reader.

Structure and Writing Style

I.  General Points to Consider

When considering whether to include content in an appendix, keep in mind the following points:

• It is usually good practice to include your raw data in an appendix, laying it out in a clear format so the reader can re-check your results. Another option if you have a large amount of raw data is to consider placing it online and note this as the appendix to your research paper.
• Any tables and figures included in the appendix should be numbered as a separate sequence from the main paper . Remember that appendices contain non-essential information that, if removed, would not diminish a reader's understanding of the overall research problem being investigated. This is why non-textual elements should not carry over the sequential numbering of elements in the paper.
• If you have more than three appendices, consider listing them on a separate page at the beginning of your paper . This will help the reader know before reading the paper what information is included in the appendices [always list the appendix or appendices in a table of contents].
• The appendix can be a good place to put maps, photographs, diagrams, and other non-textual elements , if you feel that it will help the reader to understand the content of your paper, but remembering that the paper should be understandable without them.
• An appendix should be streamlined and not loaded with a lot information . If you have a very long and complex appendix, it is a good idea to break it down into separate appendices, allowing the reader to find relevant information quickly.

II.  Contents

Appendices may include some of the following, all of which should be referred to or summarized in the text of your paper:

• Supporting evidence [e.g. raw data]
• Contributory facts or specialized data [raw data appear in the appendix, but with summarized data appearing in the body of the text].
• Sample calculations
• Technical figures, graphs, tables, statistics
• Detailed description of research instruments
• Maps, charts, photographs, drawings
• Letters, emails, and other copies of correspondance
• Questionnaire/survey instruments, with the results appearing in the text
• Complete transcripts of interviews
• Complete field notes from observations
• Specification or data sheets

NOTE:   Do not include vague or irrelevant information in an appendix; this additional information will not help the reader’s overall understanding and interpretation of your research and may only succeed in distracting the reader from understanding your research study.

III.  Format

Here are some general guideline on how to format appendices, but consult the writing style guide [e.g., APA] your professor wants you to use for the class, if needed:

• Appendices may precede or follow your list of references.
• Each appendix begins on a new page.
• The order they are presented is dictated by the order they are mentioned in the text of your research paper.
• The heading should be "Appendix," followed by a letter or number [e.g., "Appendix A" or "Appendix 1"], centered and written in bold.
• Appendices must be listed in the table of contents [if used].
• The page number(s) of the appendix/appendices will continue on with the numbering from the last page of the text.

Appendices . The Structure, Format, Content, and Style of a Journal-Style Scientific Paper. Department of Biology. Bates College; Tables, Appendices, Footnotes and Endnotes . The Writing Lab and The OWL. Purdue University; Lunsford, Andrea A. and Robert Connors. The St. Martin's Handbook. New York: St. Martin's Press, 1989.

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General research paper guidelines: appendices.

If you have some information you would like to include in your research but it could potentially be distracting to readers or inappropriate within the body of your research paper, you can always include supplemental information as an appendix to your work. An appendix or appendices should always be inserted after your Reference List; however, the appropriateness of appendix content really depends on the nature and scope of your research paper.

For a more in-depth review of what supplemental materials might be included in a social science appendix, be sure to review Section 2.14 “Appendices” (pp. 41-42) of your 7 th edition APA manual.

Appendices Formatting

APA 7 addresses appendices and supplemental materials in Section 2.14 and on page 41:

• The appendices follow the reference list.
• They are lettered "Appendix A," "Appendix B," "Appendix C," and so forth. If you have only one appendix, however, simply label it Appendix.
• Put figures and tables in separate appendices. The appendix title serves as the title for a table if it is the only table in the appendix.
• If you decide that certain figures and tables should appear in the same appendix, number them A1, A2, A3, and so forth, according to the appendix in which they appear.
• The materials in the appendix must not extend beyond the margins of the rest of the paper: Reduce the appendix materials as needed.

As a general guide, appendices are appropriate for any material that, if presented in the main body of the document, would unnecessarily interrupt the flow of the writing. Note that it is unlikely that you will use appendices in Walden course papers. For doctoral capstone studies, you might include some appendices with supplementary information.

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Supplementing the text: the role of appendices in academic papers

Keith S. Taber Faculty of Education, University of Cambridge, UK. E-mail: [email protected]

Appendices have advantages over separate supplementary documents

The editorial policy at CERP is to avoid publishing discrete supplementary materials of a form that could be included in the article file (text, diagrams, tables, etc. ), but rather to include such supplementary information as appendices, annexes added to the end of the article text. This has an advantage for readers working with downloaded articles, as if they find something of interest that is referred to in the main text as being available in the appendices, it can be immediately accessed in the same document file – rather than having to go on-line and download a separate file. This means the appendix will be part of the same document as the main text and so share its DOI (Digital Object Identifier, the unique reference number that allows on-line materials to be readily located even if their location – URL – changes). If preferred, the downloaded file could be electronically duplicated by a reader so that the appendix can be displayed alongside the relevant part of the main text. (Note, however, that downloaded files should not be used to make copies of articles for other readers – see Appendix 1.)

Including material in the main article file also makes it clearly part of the ‘version of record’ (VOR) of an article. The VOR is the officially published version that represents ‘the’ journal article, rather than the author's manuscript version submitted for peer review or an accepted version that has not yet been subjected to final formatting and proofing. The VOR of a CERP article will include the main manuscript text (often interspersed with figures, tables, etc. ), references, and possibly one or more appendices. The appendices are clearly part of the published article, and so part of the intellectual property of the author that has been licensed to the publisher. So if another scholar wishes to refer to something in an article's appendix it is clear they should cite the article to which the appendix belongs – something the author of the article is likely to appreciate given that it has been suggested that “supplemental materials are typically not cited on their own” ( Feeney, 2010, p. 29 ).

Appendices can make articles longer, but when used appropriately this is not a problem for readers. The main text of the article should be self contained so it can be fully understood without referring to the appendices: “all key information should be included in the main text of the manuscript” ( Taber et al. , 2014, p. 318 ). Appendices therefore contain relevant, but subsidiary information: a reader may wish to turn to the appendices when these are referred to by the author, but could instead simply choose to carry on reading the main text of the article without taking a detour to the appendices. For many readers, appendices will offer technical material that is of less interest than the main text, but the assumption is that appendices will contain material that will be seen of interest by some readers.

What should be appended?

An article in a research journal needs to offer an argument, supported by evidence, for some new contribution to ‘public knowledge’ (a notion which can be considered problematic, but remains useful – see Appendix 2). That is, published articles are considered to make knowledge claims that go beyond the existing canon of (previously) published scholarship. The article needs to therefore include sufficient text to make the argument clearly and to set out the evidential basis for the claim. However, articles should also be succinct as possible to support the reader in following the flow of the argument, and avoiding distractions and diversions. (This is especially important in an international journal where many readers will be accessing the text in an additional language, and indeed many authors will themselves not be writing in their native language.) Sometimes readers access papers for more specific, and so more limited, reasons than to read the entire study (perhaps to learn about the application of a particular research technique) – or at least choose to seek out particular information (the context of the research; the conclusions reached; the research design employed) as the basis for deciding whether they wish to commit time to reading the full paper. As there is nothing to stop any reader skimming an article, or skipping sections they are less interested in, material should not be relegated to an appendix simply to reduce the reading load of a study: the assumption is that material is placed in an appendix because it is considered subsidiary to the basic narrative being offered in the article and so is not necessary to the main thread of the argument made. (The appendices included below are meant to model this structure, although their contents might be considered more suitable for footnotes than appendices.)

Data collected is only as good as data collection instrumentation – so readers may be interested in seeing examples of questionnaires, assessment items, observation schedules, or – when using some forms of research methodology – the development of data coding protocols or the like. Some studies depend upon statistical analyses of data that can be presented with brevity without compromising the quality or strength of the argument. Other studies depend upon the interpretation of extensive qualitative data sets, and may require the presentation of a good deal of supportive quotations from the data to fully illustrate and exemplify the analysis reported. This can lead to a tension between the imperatives for brevity and thoroughness ( Pope and Denicolo, 1986 ). A solution here may be that results and limited illustratory examples are included in a main text, but appendices used to supplement this. So, for example, in an interpretative study where data analysis leads to four or five key themes the results section of the paper reporting the study may be limited to offering descriptions of the themes supported by limited quotes from the data, but an appendix might be used to illustrate the extent to which the data collected offers extensive evidence to support one of the themes reported.

Appendices may contain material related to any aspect of the work reported. The APA Publication manual ( American Psychological Association, 2009 ) used as a reference by many journals in education and the social sciences gives the example of listing in an appendix the canon of studies accessed in a meta-analysis where not all of the studies included in the study will appear in the reference list (which should only contain works directly cited in the article). An article on preparing studies for publication in chemistry education suggests that “examples of course materials developed or evaluated in a study, examples of how data were analysed ( e.g. factor analysis), examples of interview transcripts or observation notes to illustrate how the data were coded and analysed, and other materials of these kinds may sometimes be considered suitable for including as appendices ( Taber et al. , 2014, p. 318 ).

Using appendices

Appendices need to be called out at appropriate points in the text: that is, the author must indicate to readers somewhere in the main text that there is relevant supplementary information in an appendix. If there is no suitable point in the main narrative of the study to refer a reader to an appendix then it has no place in the article and should be omitted (in the same way that any table or figure appearing in an article has to be called out in the text). Moreover, appendices should be numbered according to when they are first called out – as is the practice with figures and tables. (That is a reader following the main text should not meet ‘see Appendix 2’ before they have met ‘see Appendix 1’.)

It may well be that there is good reason to refer to the same appendix at several points in the main text, and so subsequent references to an appendix may be out of order. (That is, a reader may be referred to Appendix 1, then to Appendix 2, then later to Appendix 1 again.) If the different references to the same appendix are pointing to different information within the appendix, this may – but would not necessarily – indicate that the appendix would be better split. So for example, an appendix could present background information in the form of biographical sketches of three teachers participating in a study, and it may be open to question whether these are best presented in the same appendix, or would better be split into different appendices. There are nuanced judgements to be made about such matters. If the study was a multiple case study of the professional work of the three teachers (so that the data from each teacher was analysed separately, and results reported discretely in the findings before a cross-case discussion) then separate appendices may seem more in keeping with the methodological approach, whereas if the data relating to the three teachers had been analysed together and fed into a unitary report of findings then placing the sketches in different appendices seems less appropriate – even if this means the reader is pointed to the same appendix at several points in the main text where the different teachers' backgrounds may be considered to be pertinent to the findings.

Reviewers and editors should be sensitive to the need for such professional judgement in deciding the nature of appendices included in an article. It may be a matter of professional opinion whether some statistical analyses are peripheral to the main theme of a study, and are better relegated to an appendix; or whether some of the ‘thick description’ needed to give the required context for naturalistic case studies can be considered less relevant background and does not need to appear in the main text of a manuscript. Generally authors' choices should be respected, and certainly article length is not by itself a good reason to ask authors to move information from the main body of the report of a study. However, authors should be sensitive to the general points made above, and ensure when preparing their manuscripts that any appendices included are relevant (but not central) to the study; discrete; suitably titled and correctly sequenced.

Appendix 1. Rationale for the restriction on copying and sharing downloaded journal articles

Even though CERP is a free to access journal, downloaded articles are for personal use, and respecting this supports the journal by giving the publisher (the Royal Society of Chemistry, RSC) a realistic sense of the readership of published articles. The RSC is able to offer access to CERP free to all readers due to generous support of the journal by the RSC's Education Division which recognises the educational value of making CERP available to readers such as school teachers, and researchers and lecturers in institutions in developing countries with limited library budgets. Part of the justification for committing resources to CERP in this way is that CERP reaches a large and diverse readership, and the main measure of that is the number of article downloads from the journal site. Readers will therefore help the journal, and support the argument for keeping it free to access, by notifying colleagues of articles likely to be of interest, and sending them links to the articles on-line, but not sending copies of the downloaded files they have been provided for their own personal use.

Appendix 2. The notion of public knowledge in relation to journal articles

In science it is not enough to discover something ( i.e. develop new personal knowledge), rather it must be shared with the scientific community through publication. Research journals are the main means of communication of scientific results, and so of adding to public knowledge in scientific fields. Prestigious journals normally have a criterion for accepting an article for publication that it offers some significant new knowledge not previously published, and so adds to public knowledge. So when a researcher undertakes some scholarship or empirical work that leads them to develop new (personal) knowledge that they believe is not already known in the community (in effect, published) they write up for a research journal. If the process of peer review leads to an evaluation that the knowledge claims being made are both sound and represent an original contribution then the article is published and contributes to an expanded public knowledge.

When discussed in these terms the idea of public knowledge seems quite straightforward, and the account in the previous paragraph would probably seem familiar and reasonable to most readers of this editorial. However, the notion of public knowledge may seem quite problematic when viewed from certain perspectives on the nature of knowledge itself. So, for example, a personal constructivist notion of knowledge might require knowledge to have a (personal) knower, and consider that knowledge is a property of mind, and furthermore a mental construction produced by perceptual-cognitive processes ( Taber, 2013 ). From this perspective journal articles do not contain knowledge as such (as knowledge only exists in minds), but rather representations of their authors' knowledge. These representations then have to be interpreted by readers as material for producing their own personal knowledge which will necessary depend upon the interpretive resources each reader has available, and so will potentially be idiosyncratic. A judgement of whether an article submitted for publication offers something not already part of public knowledge is from this standpoint inevitably a matter of interpretation and includes an inherent subjective element (as no two journal reviewers, no matter how expert, will have the ‘same’ notion of the current state of public knowledge in a field).

Academic journals may be the tools for making knowledge publicly accessible, but ‘public knowledge’ (if such an idea is given credence) is distributed (in the sense that it is spread over all the people said to know that knowledge) and manifold (in the sense that there is not a single unique authorised version of the knowledge copied around, but rather a potentially large set of unique personal takes on what that knowledge is). From such a perspective public knowledge as something uniform and shared – completely agreed upon – in a community is a fiction, albeit a useful fiction that can act as a referent when discussing academic norms and processes (see Taber, 2013, chapter 10 ).

• American Psychological Association, (2009), Publication Manual of the American Psychological Association , 6th edn, Washington DC: American Psychological Association.
• Feeney P., (2010), DOIs for Journals: Linking and beyond, Information Standards Quarterly , 22 (3), 27–31.
• Pope M. L. and Denicolo P., (1986), Intuitive theories – a researcher's dilemma: some practical methodological implications, Brit. Educ. Res. J. , 12 (2), 153–166.
• Taber K. S., (2013), Modelling Learners and Learning in Science Education: Developing representations of concepts, conceptual structure and conceptual change to inform teaching and research, Dordrecht: Springer.
• Taber K. S., Towns M. H. and Treagust D. F., (2014), Preparing chemistry education research manuscripts for publication, in Bunce D. M. and Cole R. S. (ed.), Tools of Chemical Education Research , Washington DC: American Chemical Society, pp. 299–332.

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How to Write an Appendix

Last Updated: October 4, 2023 Approved

This article was co-authored by Stephanie Wong Ken, MFA . Stephanie Wong Ken is a writer based in Canada. Stephanie's writing has appeared in Joyland, Catapult, Pithead Chapel, Cosmonaut's Avenue, and other publications. She holds an MFA in Fiction and Creative Writing from Portland State University. wikiHow marks an article as reader-approved once it receives enough positive feedback. This article has 16 testimonials from our readers, earning it our reader-approved status. This article has been viewed 1,698,716 times.

Like the appendix in a human body, an appendix contains information that is supplementary and not strictly necessary to the main body of the writing. An appendix may include a reference section for the reader, a summary of the raw data or extra details on the method behind the work. You may be required to write an appendix for school or you may decide to write an appendix for a personal project you are working on. You should start by collecting content for the appendix and by formatting the appendix properly. You should then polish the appendix so it is accessible, useful, and engaging for your reader.

Collecting Content for the Appendix

• Raw data may include sample calculations that you refer to in the body of the paper as well as specialized data that expands on data or information you discuss in the paper. Raw statistical data can also be included in the appendix.
• You may also include contributory facts from other sources that will help to support your findings in the paper. Make sure you properly cite any information you are pulling from other sources.

• You may include graphs or charts you have created yourself or graphs or charts from another source. Make sure you properly cite any visuals that are not your own in the appendix.

• For example, you may note in the appendix: “All interviews and surveys were conducted in person in a private setting and were recorded with a tape recorder.”

• You should also include any correspondences you had with subjects in your research, such as copies of emails, letters, or notes written to or from your research subjects.

Formatting the Appendix

• If you have more than one appendix, order them by letter or number and be consistent about the ordering. For example, if you are using letters, make sure the appendices are titled “Appendix A,” “Appendix B,” etc. If you are using numbers, make sure the appendices are titled “Appendix 1,” “Appendix 2,” etc.
• If you have more than one appendix, make sure each appendix begins on a new page. This will ensure the reader is not confused as to where one appendix ends and another begins.

• For example, if raw data is mentioned in the first line of your paper, place that raw data first in your appendix. Or if you mention interview questions at the very end of your paper, make sure the interview questions appear as the last point in your appendix.

• You should also make sure you list the appendix in your table of contents for the paper, if you have one. You can list it based on title, for example, “Appendix”, or “Appendix A” if you have more than one appendix.

• For example, if the text ends on page 17, continue numbering from page 17 when you put in the page numbers for the appendix.

Polishing the Appendix

• You may find it helpful to have someone else read through the appendix, such as a peer or a mentor. Ask them if they feel all the included information is relevant to the paper and remove any information they deem unnecessary.

• Read through the appendix backwards so you can make sure there are no spelling errors. You want the appendix to appear as professional as possible.

• For example, you may note an appendix in the text with: “My research produced the same results in both cases (see Appendix for raw data)” or “I feel my research was conclusive (see Appendix A for interview notes).”

Sample Appendices

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• ↑ https://libguides.usc.edu/writingguide/appendices
• ↑ http://libguides.usc.edu/writingguide/appendices
• ↑ https://askus.library.wwu.edu/faq/116707

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To write an appendix, start by writing “Appendix” at the top of the document, using the same font you used for your chapter headings. Then, order the contents, such as graphs, surveys, or interview transcripts, based on the order in which they appear in your paper. Next, number the pages so they follow sequentially, coming after your paper and your reference list or list of sources. Finally, make sure to check for spelling and grammar errors, so everything will look polished and professional. For more tips from our English co-author, including how to refer to the appendix in your paper, keep reading! Did this summary help you? Yes No

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• Research Paper Appendix | Example & Templates

Research Paper Appendix | Example & Templates

Published on 15 August 2022 by Kirsten Dingemanse and Tegan George. Revised on 25 October 2022.

An appendix is a supplementary document that facilitates your reader’s understanding of your research but is not essential to your core argument. Appendices are a useful tool for providing additional information or clarification in a research paper , dissertation , or thesis without making your final product too long.

Appendices help you provide more background information and nuance about your topic without disrupting your text with too many tables and figures or other distracting elements.

We’ve prepared some examples and templates for you, for inclusions such as research protocols, survey questions, and interview transcripts. All are worthy additions to an appendix. You can download these in the format of your choice below.

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Table of contents

What is an appendix in a research paper, what to include in an appendix, how to format an appendix, how to refer to an appendix, where to put your appendices, other components to consider, appendix checklist.

In the main body of your research paper, it’s important to provide clear and concise information that supports your argument and conclusions . However, after doing all that research, you’ll often find that you have a lot of other interesting information that you want to share with your reader.

While including it all in the body would make your paper too long and unwieldy, this is exactly what an appendix is for.

As a rule of thumb, any detailed information that is not immediately needed to make your point can go in an appendix. This helps to keep your main text focused but still allows you to include the information you want to include somewhere in your paper.

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An appendix can be used for different types of information, such as:

• Supplementary results : Research findings  are often presented in different ways, but they don’t all need to go in your paper. The results most relevant to your research question should always appear in the main text, while less significant results (such as detailed descriptions of your sample or supplemental analyses that do not help answer your main question), can be put in an appendix.
• Statistical analyses : If you conducted statistical tests using software like Stata or R, you may also want to include the outputs of your analysis in an appendix.
• Further information on surveys or interviews : Written materials or transcripts related to things such as surveys and interviews can also be placed in an appendix.

You can opt to have one long appendix, but separating components (like interview transcripts, supplementary results, or surveys) into different appendices makes the information simpler to navigate.

Here are a few tips to keep in mind:

• Always start each appendix on a new page.
• Assign it both a number (or letter) and a clear title, such as ‘Appendix A. Interview transcripts’. This makes it easier for your reader to find the appendix, as well as for you to refer back to it in your main text.
• Number and title the individual elements within each appendix (e.g., ‘Transcripts’) to make it clear what you are referring to. Restart the numbering in each appendix at 1.

It is important that you refer to each of your appendices at least once in the main body of your paper. This can be done by mentioning the appendix and its number or letter, either in parentheses or within the main part of a sentence. It is also possible to refer to a particular component of an appendix.

Appendix B presents the correspondence exchanged with the fitness boutique. Example 2. Referring to an appendix component These results (see Appendix 2, Table 1) show that …

It is common to capitalise ‘Appendix’ when referring to a specific appendix, but it is not mandatory. The key is just to make sure that you are consistent throughout your entire paper, similarly to consistency in capitalising headings and titles in academic writing.

However, note that lowercase should always be used if you are referring to appendices in general. For instance, ‘The appendices to this paper include additional information about both the survey and the interviews.’

The simplest option is to add your appendices after the main body of your text, after you finish citing your sources in the citation style of your choice . If this is what you choose to do, simply continue with the next page number. Another option is to put the appendices in a separate document that is delivered with your dissertation.

Remember that any appendices should be listed in your paper’s table of contents .

There are a few other supplementary components related to appendices that you may want to consider. These include:

• List of abbreviations : If you use a lot of abbreviations or field-specific symbols in your dissertation, it can be helpful to create a list of abbreviations .
• Glossary : If you utilise many specialised or technical terms, it can also be helpful to create a glossary .
• Tables, figures and other graphics : You may find you have too many tables, figures, and other graphics (such as charts and illustrations) to include in the main body of your dissertation. If this is the case, consider adding a figure and table list .

Checklist: Appendix

All appendices contain information that is relevant, but not essential, to the main text.

Each appendix starts on a new page.

I have given each appendix a number and clear title.

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What You Need to Know About the Manuscript Appendix

Research papers are packed with information; however, not all of it needs to be included in your main paper. Although you want to share all of it, your paper should focus on only those data that are relevant to your hypothesis and conclusions. So, what do you do with the rest of the data? Where do you put it so that anyone interested can find it? The answer to the question is appendix. Let us find out more about it.

What’s in an Appendix?

An appendix comprises additional information that was gathered during your research but that you will not include in your paper. Many times, your data analyses are too detailed to be included in your main text . This might include lengthy spreadsheets of data.

You want your readers to stay focused on your main discovery but also want additional information to be available to them. Your readers can peruse an appendix at will but won’t have to use it to understand your research.

Points to Remember

When creating your appendix, remember :

• The data in the appendix should not be essential to understanding your paper;
• Your paper must include references to all the appendices; and
• Your appendix is presented in the order it is cited in the text.

What You Might Include

The kind of data that an appendix may include :

• Letters from other researchers or interested parties;
• Questionnaires (with proper citations if not created);
• Graphical illustrations and tables not needed in the main text.
• List of terms or acronyms and abbreviations (although author guidelines might prefer that these be included in the main text);
• Excerpts from other relevant documents (with proper citations); and
• Raw data (compiled in table format).

Appendix Format

An appendix is formatted in much the same way as your main text. It has a title page labeled with a numeral or letter in the order in which it is cited in your text. Subtopics (or “subheaders”) are also labeled using the same format.

For example:

• Title : Appendix A: Data from Site 323 (the first appendix to be cited in the text).
• Subheader : 1: Data on Male Species .
• Tables/Figures : Table A1. Fecundity of Females in Second Year (figures would follow the same formatting).

The second appendix would be labeled “Appendix B” with the same designations for subheaders, tables, and figures. Keep the author guidelines in mind for specifics on citing appendices in your main text.

Appendix pages are consecutively numbered following your main text (i.e., if your text ends on page 35, your appendix will begin with page 36).

Appendix Organization

Consider your audience and the role you want your appendix to play as supplementary information. It is information that is not necessary, but might be valuable to some. Organization is key to a valuable appendix. Remember :

• Don’t use your appendix as a “dumping ground” for all your notes;
• Don’t have an appendix that is so full of information that the main points of your master paper get buried;
• Do ensure that you cite all references to other research and publications; and
• Do include the appendices in your table of contents.

Where Does It Go?

Placement of your appendix (or appendices, if more than one) depends on the target journal’s style guide. Some style guides, such as the American Psychiatric Association , place appendices after tables and figures. Others might ask you to include appendices before or after your references . Check your author guidelines for protocols.

Have you used appendices as supplements to your research paper ? If so, what did you include in it and why? Please let us know your thoughts in the comment section below.

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StatPearls [Internet].

Appendicitis.

Mark W. Jones ; Richard A. Lopez ; Jeffrey G. Deppen .

Affiliations

Last Update: April 24, 2023 .

• Continuing Education Activity

Appendicitis is the inflammation of the vermiform appendix. It typically presents acutely, within 24 hours of onset, but can also present as a more chronic condition. Classically, appendicitis initially presents with generalized or periumbilical abdominal pain that later localizes to the right lower quadrant. This activity reviews the presentation, evaluation, and treatment of appendicitis and stresses the role of the interprofessional team in evaluating and treating patients with this condition.

• Describe the common and uncommon presentations of appendicitis.
• Outline the evaluation of a patient with appendicitis.
• Explain the treatment options for patients with appendicitis.
• Explain the importance of improving care coordination among the interprofessional team to enhance the early diagnosis, evaluation, and provision of care for patients with appendicitis.
• Introduction

Appendicitis is inflammation of the vermiform appendix. Appendix a hollow organ located at the tip of the cecum, usually in the right lower quadrant of the abdomen. However, it can be located in almost any area of the abdomen, depending on if there were any abnormal developmental issues, including midgut malrotation, or if there are any other special conditions such as pregnancy or prior abdominal surgeries. The appendix develops embryonically in the fifth week. There is a rotation of the midgut to the external umbilical cord with the eventual return to the abdomen and rotation of the cecum. This results in the usual retrocecal location of the appendix. It is often a disease of acute presentation, usually within 24 hours, but it can also present as a more chronic condition. If there has been a perforation with a contained abscess, the presenting symptoms can be more indolent. The exact function of the appendix has been a debated topic. Today it is accepted that this organ may have an immunoprotective function and acts as a lymphoid organ, especially in the younger person. Other theories contend that the appendix acts as a storage vessel for "good" colonic bacteria. Still, others argue that it is a mere developmental remnant and has no real function. [1] [2] [3] [4]

The cause of appendicitis is usually an obstruction of the appendiceal lumen. This can be from an appendicolith (stone of the appendix) or some other mechanical etiologies. Appendiceal tumors such as carcinoid tumors, appendiceal adenocarcinoma, intestinal parasites, and hypertrophied lymphatic tissue are all known causes of appendiceal obstruction and appendicitis. Often, the exact etiology of acute appendicitis is unknown. When the appendiceal lumen gets obstructed, bacteria build up in the appendix and cause acute inflammation with perforation and abscess formation. One of the most popular misconceptions is the story of the death of Harry Houdini. After being unexpectedly punched in the abdomen, the rumor goes that his appendix ruptures, causing immediate sepsis and death. The facts are that Houdini did die from sepsis and peritonitis from a ruptured appendix, but it had no connection to him being struck in the abdomen. It was more related to widespread peritonitis and the limited availability of effective antibiotics. [5] [6]  The appendix contains aerobic and anaerobic bacteria, including Escherichia coli and Bacteroides spp . However, recent studies utilizing next-generation sequencing revealed a significantly higher number of bacterial phyla in patients with complicated perforated appendicitis. [7]

• Epidemiology

Appendicitis occurs most often between the ages of 5 and 45, with a mean age of 28. The incidence is approximately 233/per 100,000 people. Males have a slightly higher predisposition to developing acute appendicitis than females, with a lifetime incidence of 8.6% and 6.7% for men, and women, respectively. Approximately 300,000 hospital visits yearly in the United States for appendicitis-related issues. [8]

• Pathophysiology

The pathophysiology of appendicitis likely stems from obstruction of the appendiceal orifice. The background etiology of the obstruction might differ in the different age groups. While lymphoid hyperplasia is essential, this results in inflammation, localized ischemia, perforation, and the development of a contained abscess or frank perforation with resultant peritonitis. This obstruction may be caused by lymphoid hyperplasia, infections (parasitic), fecaliths, or benign or malignant tumors. When an obstruction is the cause of appendicitis, it leads to an increase in intraluminal and intramural pressure, resulting in small vessel occlusion and lymphatic stasis. Once obstructed, the appendix fills with mucus and becomes distended, and as lymphatic and vascular compromise advances, the wall of the appendix becomes ischemic and necrotic. Bacterial overgrowth then occurs in the obstructed appendix, with aerobic organisms predominating in early appendicitis and mixed aerobes and anaerobes later in the course. Common organisms include Escherichia coli , Peptostreptococcus , Bacteroides , and  Pseudomonas . Once significant inflammation and necrosis occur, the appendix is at risk of perforation, leading to a localized abscess and sometimes frank peritonitis. [9]  The most common position of the appendix is retrocecal. While the anatomical position of the root of the appendix is mostly constant, tail positions can vary. Possible positions include retrocecal, subcecal, pre-and post-ileal, and pelvic.

• Histopathology

Microscopic findings in acute appendicitis include the proliferation of neutrophils of the muscularis propria. The degree and extent of inflammation are directly proportionate to the severity of the infection and duration of the disease. As this condition progresses, extra appendiceal fat and surrounding tissues become involved in the inflammatory process. [10]

• History and Physical

Typically, appendicitis presents as an initial generalized or periumbilical abdominal pain that localizes to the right lower quadrant. Initially, the visceral afferent nerve fibers at T8 through T10 are stimulated, leading to vague centralized pain. As the appendix becomes more inflamed and the adjacent parietal peritoneum is irritated, the pain becomes more localized to the right lower quadrant. Pain may or may not be accompanied by any of the following symptoms:

• Nausea/vomiting
• Fever (40% of patients)
• Generalize malaise
• Urinary frequency or urgency [11]

Uncommon Presentations

Some patients may present with uncommon features. In these patients, the pain may have woken the patient up from sleep. In addition, the patients may complain of pain while walking or coughing.

Pain upon passive extension of the right leg with the patient in the left lateral decubitus position is known as the psoas sign. This maneuver stretches the psoas major muscle, which can be irritated by an inflamed retrocecal appendix. Patients often flex the hip to shorten the psoas major muscle and relieve pain. [12]

Physical exam findings are often subtle, especially in early appendicitis. As inflammation progresses, signs of peritoneal inflammation develop. Signs include:

• Right lower quadrant guarding and rebound tenderness over McBurney's point (1.5 to 2 inches from the anterior superior iliac spine (ASIS) on a straight line from the ASIS to the umbilicus)
• Rovsing's sign (right lower quadrant pain elicited by palpation of the left lower quadrant)
• Dunphy's sign (increased abdominal pain with coughing)

Other associated signs such as the psoas sign (pain on external rotation or passive extension of the right hip suggesting retrocecal appendicitis) or obturator sign (pain on internal rotation of the right hip suggesting pelvic appendicitis) are rare. The time course of symptoms is variable but typically progresses from early appendicitis at 12 to 24 hours to perforation at greater than 48 hours. Seventy-five percent of patients present within 24 hours of the onset of symptoms. The risk of rupture is variable but is about 2% at 36 hours and increases about 5% every 12 hours after that.

Several practical scores have been defined to facilitate the prompt diagnosis of acute appendicitis, mainly based on the history and physical examination, accompanied by laboratory tests and imaging measures, including abdominal ultrasonography. Accordingly, evaluation of patients with suspicious signs and symptoms suggestive of acute appendicitis has been widely undertaken with Alvarado criteria since 1986. The highest score among Alvarado criteria is allocated to the tenderness in the right iliac fossa, leukocytosis, and each of the other predicted symptoms, including migratory right iliac fossa pain, nausea, and or vomiting, and anorexia, hold one score. Moreover, positive findings in the remaining indexes of physical examination, including fever and rebound tenderness in the right iliac fossa, would hold a similar score of one. [13]  

The emergency department physician must refrain from giving the patient any pain medication until the surgeon has seen the patient. The analgesics can mask the peritoneal signs and lead to a delay in diagnosis or even a ruptured appendix.

Lab Testing

Laboratory measurements, including total leucocyte count, neutrophil percentage, and C-reactive protein (CRP) concentration, are requested to proceed with diagnostic steps in patients with suspected acute appendicitis. [14]  Elevated white blood cells count (WBC) with or without a left shift or bandemia is classically present, but up to one-third of patients with acute appendicitis will present with a normal WBC count. There are usually ketones found in the urine, and the C-reactive protein may be elevated. A combination of normal WBC and CRP results has a specificity of 98% for the exclusion of acute appendicitis. Moreover, the WBC and CRP results have a positive predictive value to differentiate uninflamed, uncomplicated, and complicated appendicitis.   Both increasing levels of CRP and WBC correlate with a significant increase in the likelihood of complicated appendicitis. The possibility of a patient having appendicitis with both normal values of WBC and CRP level is extremely low. [15]  The WBC count of 10,000 cells/mm^3 is highly predictable in patients with acute appendicitis; however, the level would increase in patients with complicated appendicitis. Accordingly, the WBC count of equal and or above 17,000 cells/mm^3 is associated with complications of acute appendicitis, including perforated and gangrenous appendicitis.

Appendicitis is traditionally a clinical diagnosis. However, several imaging modalities are used to proceed with the diagnostic steps, including an abdominal CT scan, ultrasonography, and MRI.

An abdominal CT scan has greater than 95% accuracy for the diagnosis of appendicitis and is used with increasing frequency. CT criteria for appendicitis include an enlarged appendix (greater than 6 mm in diameter), appendiceal wall thickening (greater than 2 mm), peri-appendiceal fat stranding, appendiceal wall enhancement, the presence of appendicolith (approximately 25% of patients). It is unusual to see air or contrast in the lumen with appendicitis due to luminal distention and possible blockage in most cases of appendicitis. Non visualization of the appendix does not rule out appendicitis. Ultrasound is less sensitive and specific than CT but may be useful to avoid ionizing radiation in children and pregnant women. MRI may also be useful for pregnant patients with suspected appendicitis and an indeterminate ultrasound. Classically the best way to diagnose acute appendicitis is with a good history and detailed physical exam performed by an experienced surgeon; however, it is very easy to get a CT scan done in the emergency department. It has become common practice to rely mostly on the CT report to make the diagnosis of acute appendicitis. Occasionally appendicoliths are incidentally found on routine x-rays or CT scans. The major concern with obtaining an abdominopelvic CT scan is radiation exposure; however, the average exposure with a typical CT would not exceed 4 mSv, which is slightly above the background exposure of almost 3 mSv. Despite the higher resolution of CT images obtained with the maximal radiation of 4 mSv, lower exposures would not affect the clinical outcomes. Moreover, obtaining an IV-contrast abdominopelvic CT scan in patients suspicious of acute appendicitis should be limited to an acceptable glomerular filtration rate (GFR) equal to or above 30 ml/min. These patients are at a higher risk of developing appendicitis than the general population. These patients should be considered for prophylactic appendectomies. Studies have also shown a 10 to 30% incidence of appendicoliths present in appendectomy specimens done for acute appendicitis. [16] [17] [18]  

Ultrasonography 

Abdominal ultrasonography is a widely used and available primary measure to evaluate patients with acute abdominal pain. A specific index of compressibility along with a diameter of less than 5 mm is used to exclude appendicitis. On the contrary, several evidence, including an anteroposterior diameter of above 6 mm, an appendicolith, and abnormally increased echogenicity of the peri-appendiceal fat, are suggestive of acute appendicitis. The major concerns with using abdominal ultrasonography to evaluate the potential diagnosis of acute appendicitis are the innate limitations of the sonography in obese patients and the operator-dependency to find the suggestive features. Moreover, patients complicated with peritonitis would hardly tolerate the graded compression. [19]

Despite the high sensitivity and specificity of MRI in the context of acute appendicitis identification, major concerns with obtaining an abdominal MRI exist. Performing an abdominal MRI is not only expensive but also demands a high level of expertise to interpret the results. Therefore, its indications are mainly limited to special groups of patients, including pregnant women in whom an unacceptable risk of radiation exposure is embedded. [20]

• Treatment / Management

In the emergency department, the patient must be kept nil per os (NPO) and hydrated intravenously with crystalloid, and antibiotics should be administered intravenously as per the surgeon. The responsibility for the consent falls on the surgeon. The gold-standard treatment for acute appendicitis is to perform an appendectomy. Laparoscopic appendectomy is preferred over the open approach. Most uncomplicated appendectomies are performed laparoscopically. Several studies have compared the outcomes with the laparoscopic appendectomy group and patients who underwent open appendectomy. The results were suggestive of a lower incidence of wound infection, decreased level of postoperative analgesic requirement, and shorter postoperative hospital stays in the former group. The main disadvantage of laparoscopic appendectomy is the longer operative time. [21]  

In cases where there is an abscess or advanced infection, the open approach may be needed. The laparoscopic approach affords less pain, quicker recovery, and the ability to explore most of the abdomen through small incisions. Situations, where there is a known abscess from a perforated appendix may require a percutaneous drainage procedure usually done by an interventional radiologist. This stabilizes the patient and allows the inflammation to subside over time, enabling a less difficult laparoscopic appendectomy to be performed at a later date. Practitioners also start patients on broad-spectrum antibiotics. There is some disagreement regarding preoperative antibiotic administration for uncomplicated appendicitis. Some surgeons feel routine antibiotics in these cases are not warranted, while others give them routinely. There have also been several studies promoting the treatment of uncomplicated appendicitis solely with antibiotics and avoiding surgery altogether. [1] [22]  

In patients with an appendiceal abscess, some surgeons continue antibiotics for several weeks and then perform an elective appendectomy. When the appendix has ruptured, the procedure can still be done laparoscopically, but extensive irrigation of the abdomen and pelvis is necessary. In addition, the trocar sites may have to be left open. A significant number of patients with an impression of acute appendicitis can be managed with a laparoscopic approach uneventfully. However, several factors predict the demand to convert to the open approach. The only preoperative independent factor predicting the conversion during laparoscopic appendectomy is the presence of comorbidities. Moreover, a couple of intra-operative findings, including the presence of peri-appendicular abscess and diffuse peritonitis, are independent predictors of not only a higher conversion rate but also a significant increase in postoperative complications. [23]  

While laparoscopic appendectomy has been widely used as the preferred approach for the surgical management of acute appendicitis in many centers, still open appendectomy might be selected as the practical choice, specifically in the management of complicated appendicitis with phlegmon and in the patients who are subjected to the conversion from the laparoscopic approach mainly due to the potential issues related to poor visibility. Several other alternative surgical approaches, including Natural Orifice Transluminal Endoscopic Surgery (NOTES) and Single-incision Laparoscopic Surgery (SILS), have been introduced recently. The idea of utilizing a flexible endoscope to enter the gastrointestinal or vaginal tract and consequently traversing the mentioned organ to enter the peritoneal cavity is an interesting alternative for patients who are considerate about the cosmetic aspects of the procedures. It has been later tested with successful performing of trans-gastric appendectomy in a group of ten Indian patients. The major potential advantages of appendectomy with NOTES are avoiding scars and limiting postoperative pain. Regarding the limited number of patients who have been under NOTES appendectomy, a detailed comparison of postoperative outcomes is still impossible. Hence, the major drawback with performing this technique is the demand to hybrid with the laparoscopic approach is to provide adequate retraction during the procedure and to confirm the closure of the entry site. [24] [25] [26] [27] [28]  As a surgical technique, SILS for an appendectomy is performed with an incision in the umbilicus or a preexisting abdominal scar. Potential advantages of SILS include a decrease in postoperative pain, wound-related post-procedural complications, and consequent shorter periods of sick leave. [29]  However, up to 40% of patients are still converted to conventional laparoscopy at some point during the procedure. The major disadvantage of SILS for an appendectomy is a higher long-term complication related to incisional hernia.

• Differential Diagnosis

The differential diagnosis includes Crohn ileitis, mesenteric adenitis, the inflammatory process in the cecal diverticulum, mittelschmerz, salpingitis, ruptured ovarian cyst, ectopic pregnancy, tubo-ovarian abscess, musculoskeletal disorders, endometriosis, pelvic inflammatory disease, gastroenteritis, right-sided colitis, renal colic, kidney stones, irritable bowel disease, testicular torsion, ovarian torsion, round ligament syndrome, epididymitis, and other nondescript gastroenterological issues. Obtaining a detailed past medical history and performing a problem-oriented physical examination is necessary to exclude the differential diagnoses. Accordingly, recent viral infection mainly suggests acute mesenteric adenitis and rising severe cervical motion tenderness during trans-vaginal physical examinations typically present in the pelvic inflammatory disease. One of the challenging differential diagnoses is an acute presentation of Crohn disease. While a positive past medical history of Crohn disease can prevent unnecessary surgical procedures, Crohn disease might acutely present for the first time, mimicking acute appendicitis. Intra-operatively, the presence of inflamed ileum should raise the suspicion of Crohn disease along with other bacterial causes of acute ileitis, including Yersinia or Campylobacter ileitis. The preferred approach is to proceed with an appendectomy, even if there is no evidence of acute appendicitis. However, in patients with features of ileitis along with inflamed cecum, the appendectomy is contraindicated as it would be later complicated. [30]

• Surgical Oncology

Despite the non-significant annual incidence of appendiceal cancers, with 1.2 cases per 100000 in the United States, almost 30% of this spectrum might present acutely. The most common appendiceal malignancies are Gastroenteropancreatic neuroendocrine tumors (GEP-NETs), goblet cell carcinoma (GCC), colonic-type adenocarcinoma, and mucinous neoplasm. [31]  

Gastroenteropancreatic Neuroendocrine Tumors (GEP-NETs)

(GEP-NETs) are the most common histopathological subtypes. They might rarely metastasize to the liver and or lymph nodes. Therefore, in patients with suspicious GEP-NETs (carcinoid tumor), further evaluation of the liver and the ileocolic lymph node basin are essential. The primary tumor size dictates the demanding surgical steps. Accordingly, in the carcinoid tumors of less than 1-centimeter size, an appendectomy with negative margins is the only requested surgical management. Although in the carcinoid tumor of greater than 2 cm, a right hemicolectomy is indicated, the surgical plan in appendiceal carcinoid lesions of 1 to 2 cm is still equivocal. However,  in the presence of mesenteric invasion, enlarged lymph nodes, and or equivocal surgical margins, right hemicolectomy is recommended.

Goblet Cell Carcinoma

Goblet cell carcinomas are a ubiquitous entity of appendiceal malignancies in that they share the diagnostic features of both appendiceal adenocarcinoma and neuroendocrine tumors. A comprehensive peritoneal evaluation with further peritoneal cancer index score (PCIS) documentation should be undertaken. Patients with a non-metastatic and an equal or higher than 2 cm size will benefit from a right hemicolectomy. [32]

Non-Hodgkin lymphomas (NHL), and its subtypes, including mucosa-associated lymphoid tissue (MALT) lymphomas, might initially present with acute appendicitis. The surgical management of this highly uncommon appendiceal malignancy is limited to a simple appendectomy. However, a comprehensive systemic evaluation to exclude any potential metastatic site should be included. [33]

Adenocarcinoma

Adenocarcinoma of the appendix, a rare appendiceal neoplasm with three histopathological subtypes, is most commonly present with acute appendicitis. The standard treatment is performing a right hemicolectomy, irrespective of the tumor size and or the involvement of the lymph node basin. [34]

Mucocele and Mucinous Neoplasm

Appendiceal mucocele, which might result from a benign or malignant spectrum of mucosal hyperplasia, and various cystic formations, might present with acute appendicitis. Several pre-operative radiological features, including a well-encapsulated cystic structure in the right lower quadrant, would raise the impression of an appendiceal mucocele; however, definitive diagnosis requires intraoperative evaluation and histopathological reports. The preferred surgical management is an appendectomy with great cautionary measures to prevent capsular rupture. In terms of peritoneal spread, providing documentation of the peritoneal involvement, along with tissue diagnosis with biopsies, is recommended. Moreover, suspicious mucinous neoplasm of the appendix should be managed with the peritoneal examination and record the PCIS in the presence of mucin. Patient selection for the laparoscopic approach in the management of appendiceal mucocele is extremely important and is limited to those with radiologic features suggestive of a homogenous cyst. [35]

If diagnosed and treated early, as a relatively safe surgical procedure, the recovery within 24 to 48 hours, is expected. Cases that present with advanced abscesses, sepsis, and peritonitis may have a more prolonged and complicated course, possibly requiring additional surgery or other interventions.

• Complications

Postoperative abscesses, hematomas, and wound complications are all complications that can be seen after appendectomies. If the wound does get infected, one may grow Bacteroides. "Recurrent" or "stump" appendicitis can occur if too much of the appendiceal stump is left after an appendectomy. This acts just like an appendix and can become occluded and infected just as with the initial episode. Therefore, it is important to ensure that there be very minimal and preferably less than 0.5 cm appendiceal stumps after an appendectomy. If left untreated, appendicitis can lead to abscess formation with the development of an enterocutaneous fistula. Diffuse peritonitis and sepsis can also develop, which may progress to significant morbidity and possible death.

• Postoperative and Rehabilitation Care

Patients with uncomplicated appendicitis will generally experience an uneventful postoperative period, and postoperative antibiotic therapy is not required. However, the group of patients with complicated appendicitis should be planned for antibiotic therapy for an average of 4 days. Wound complications, including infections, should be managed an adequate wound opening and irrigation, followed by packing. However, antibiotic therapy is essential in the management of patients who are complicated with abscess formation and deep fascial plane involvements.

• Pearls and Other Issues

Special consideration should be given to the treatment of patients with perforated appendicitis with an abscess. Those who present with an abscess and do not exhibit peritonitis may benefit from CT or ultrasound-guided percutaneous drain placement as well as antibiotics. Interval appendectomy is classically performed 6 to 10 weeks after recovery. Historically, 20 to 40 % of patients treated medically for perforated appendicitis with an abscess had recurrent appendicitis in historical literature. More recent studies suggest these rates be much lower.

Complications of appendicitis and appendectomy include surgical site infections, intra-abdominal abscess formation (3% to 4% in open appendectomy and 9 to 24% in laparoscopic appendectomy), prolonged ileus, enterocutaneous fistula, and small bowel obstruction.

Occasionally the incorrect diagnosis of acute appendicitis is made when, in reality, the correct diagnosis is Crohn disease of the cecum or terminal ileum. It is important to know that if this occurs that the appendix should be left in place if there is involvement at its base. The removal of the appendix in this situation has a high leak and fistula rate formation. On the other hand, if the base of the appendix is spared, then the appendix should be removed, even if it appears normal. This eliminates the future confusion of diagnosing acute Crohn disease versus acute appendicitis.

In the past, it was commonplace to routinely remove the appendix at the time of other nonrelated surgeries to avoid developing appendicitis in the future. Today, however, most surgeons do not routinely remove a normal appendix at the time of other scheduled procedures. If a patient does go into surgery for an incorrect diagnosis of acute appendicitis, then it is advised to remove the appendix to avoid any future diagnostic issues.

• Enhancing Healthcare Team Outcomes

Patients with appendicitis usually first present to the emergency department with abdominal pain. The triage nurse should be familiar with the signs and symptoms of appendicitis because these patients need urgent admission and treatment to prevent perforation. However, making a diagnosis of appendicitis is not always easy.

Several guidelines exist that can help healthcare workers make a diagnosis of appendicitis. While most physicians, nurse practitioners, and physician assistants rely on the physical exam, others may obtain an ultrasound. For questionable cases, a CT scan of the abdomen may be helpful. The American College of Radiology recommends an ultrasound in pregnant women and an MRI in inconclusive cases in the same patient population. [36] [37]

While the patient is undergoing investigation, the nurse should start an IV, administer fluids as ordered. In women, a pregnancy test must be done to rule out ectopic pregnancy. The surgeon should be notified. Pain medications should typically only be administered after the surgeon has seen the patient. The nurse should monitor the patient for acute changes in pain or vital signs and report to the interprofessional team. Before surgery, the pharmacist should evaluate for potential drug-drug interactions and potential drug allergies, reporting to the team any potential concerns.

Controversy also exists on how to manage an appendiceal mass or phlegmon best and when to undertake surgery. There is no longer any question that laparoscopic appendectomy is associated with minimal pain and faster recovery, but it is costly. Other studies indicate that a single small incision provides comparable results to a laparoscopic appendectomy and is cost-effective. Given these controversies, an interprofessional team approach to diagnosis and management of appendicitis needs to be established in each institution to ensure that the patient has no morbidity and the management is cost-effective. [38]  [Level 3]

Many large series show that simple appendicitis treated either with an open or laparoscopic procedure has excellent outcomes. (Level 3)  However, more severe and complicated appendicitis is known to be associated with worse outcomes and greater utilization of resources. Further, the atypical presentation of appendicitis in pregnancy and the elderly may also make diagnosis difficult and lead to a higher incidence of complications. [39] [40]  [Level 3] In an era of managed care where quality care indices are monitored, it behooves healthcare workers to know the current standards of diagnosis and management of appendicitis or face denial of reimbursement.

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Abdomen CT, Acute Appendicitis Contributed by Scott Dulebohn, MD

Ultrasound of the right lower quadrant with findings of acute appendicitis. There is a blind ending tubular structure measuring up to 7 mm in diameter. Contributed by Kevin Carter, DO

There is acute appendicitis with a dilated fluid filled tubular structure in the right lower quadrant on this axial and sagittal images with a surrounding fluid collection and stranding due to developing abscess. Contributed by Kevin Carter, DO

Appendectomy Contributed by Sunil Munakomi, MD

Disclosure: Mark Jones declares no relevant financial relationships with ineligible companies.

Disclosure: Richard Lopez declares no relevant financial relationships with ineligible companies.

Disclosure: Jeffrey Deppen declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

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The Effects of Different Exercise Interventions on Patients with Subjective Cognitive Decline: A Systematic Review and Network Meta-Analysis

• Original Research
• Open access
• Published: 26 March 2024

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• R. Chen 1 ,
• B. Zhao 2 ,
• J. Huang 1 ,
• M. Zhang 1 ,
• Y. Wang 1 ,
• H. Liang 1 &
• Hongrui Zhan 1  

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Background and Objective

Exercise is a promising non-pharmacological therapy for subjective cognitive decline, but it is unclear which type of exercise is most effective. The objective was to assess the comparative effects and ranks of all exercise-based interventions on cognitive function in patients with subjective cognitive decline (SCD).

In this network meta-analysis, Online databases for Web of Science, PubMed, Embase, Medline, Cochrane Library and PsycINFO were searched from inception to April 30, 2023. The included studies are randomized controlled trials assessing the efficacy of exercise interventions for individuals with SCD. The primary outcome measure is memory, while secondary outcome measures encompass executive function, attention, verbal fluency, and global cognitive function. Represented using Standardized Mean Differences (SMDs) along with their 95% Confidence Intervals (CIs). Bias assessment was conducted in accordance with the ‘Cochrane Risk of Bias Assessment Tool, 2nd Edition’ (RoB 2). Pairwise meta-analysis was carried out using the ‘meta-analysis’ module within STATA 14.0, and network meta-analysis was performed using the ‘mvmeta’ and ‘network’ packages available in STATA 14.0. Registration number CRD42023289687.

This study included a total of 11 randomized controlled trials, encompassing 1,166 patients. Mind-body exercise was found to be efficacious in enhancing or sustaining memory (SMD: 0.58, 95%CI: 0.06 ∼ 1.10) and executive function (SMD: 0.41, 95%CI: 0.09 ∼ 0.73) in individuals with subjective cognitive decline. Furthermore, mind-body exercise exhibited the highest probability of being the most effective measures for improving or preventing the decline in memory (surface under cumulative ranking curve (SUCRA) value: 90.4) and executive function (SUCRA value: 91.8). The second-ranked moderate-intensity aerobic exercise has also shown a positive effect on the improvement of executive function in patients with subjective cognitive decline (SMD: 0.23, 95%CI: 0.03 ∼ 0.43, SUCRA value: 68.2). However, we did not observe a significant effectiveness of exercise interventions on verbal fluency, attention, and overall cognitive function in subjective cognitive decline.

Mind-body exercise may potentially be the optimal strategies for enhancing memory and executive function in individuals with subjective cognitive decline. Additionally, moderate-intensity aerobic exercise has shown a modest positive effect on executive function in subjective cognitive decline. When resources permit, practical application of these findings may be considered. Nevertheless, further support for the conclusions of this study is warranted through larger sample sizes and well-designed multicenter trials.

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Introduction

Subjective Cognitive Decline (SCD) refers to a decline in subjective memory or cognitive function without apparent cognitive impairments in objective cognitive assessments and without impairment in activities of daily living ( 1 ). SCD stands as an intermediate state between normal aging and Mild Cognitive Impairment (MCI), acknowledged as one of the earliest phases and initial cognitive alterations in the onset of Alzheimer’s disease (AD) ( 2 ), carrying a heightened risk of progression to MCI or AD ( 3 ). Epidemiological investigations indicate that among individuals aged 50 and older, the prevalence of SCD is 26.6% ( 4 ). SCD is associated with a 1.73-fold increased risk of progression to MCI in older adults and a 1.9-fold increased risk of progression to AD ( 5 ).

In the early stages of the AD progression, the brain can functionally compensate for neuropathological changes, thereby enabling individuals with SCD to maintain objective cognitive scores within the normal range on neuropsychological tests ( 6 ). Recent research ( 7 ) reports that individuals with SCD, despite not demonstrating significant declines in objective neuropsychological assessments, exhibit subtle impairments in global cognitive function, memory, executive function, and language abilities when compared to healthy controls. Notably, the most pronounced deterioration is observed within the domain of memory ( 7 ). While SCD does not meet the diagnostic criteria for MCI, it does share analogous patterns of cerebral alterations with patients diagnosed with MCI and those suffering from dementia attributed to AD ( 8 ).

Neuroimaging research ( 9 ) reveals that AD has undergone progressive neurofunctional deterioration and incurs irreversible cognitive impairment. Hence, the genuine promise in treating AD may lie in early intervention ( 10 ). As a preclinical stage of AD and MCI, SCD potentially represents a critical therapeutic window for slowing or preventing cognitive deterioration ( 11 ). Early intervention holds the promise of reversing cognitive decline and mitigating the risk of developing AD( 11 ). Given the limited efficacy of pharmacological interventions in enhancing cognitive function in patients with SCD, along with the potential for adverse effects, non-pharmacological interventions have garnered considerable attention for their impact on cognitive rehabilitation in SCD ( 12 ).

Exercise, as one of the non-pharmacological interventions, can modulate neuronal electrical activity associated with cognitive function, enhance brain structural plasticity ( 13 ), stimulate the generation of new neurons and synapses related to learning and memory ( 14 , 15 ), promote the secretion of neurotrophic factors such as brain-derived neurotrophic factor (BDNF) and insulin-like growth factor-1 (IGF-1) ( 16 , 17 ), to subsequently enhance cognitive function. Exercise has a positive impact on the cognitive function of individuals with SCD ( 18 , 19 ). The «Physical Activity Guidelines for Americans» ( 20 )also explicitly recommend that older individuals can enhance their cognitive function and reduce the risk of developing AD through regular physical activity.

Previous pertinent research shows that diverse forms of exercise, such as aerobic exercise (AE), resistance exercise (RE) and mind-body exercise (MBE), may potentially exert cognitive enhancement effects through the modulation of distinct molecular mechanisms outlined above, resulting in variable magnitudes of impact (e.g., MBE: standard mean difference (SMD) =0.38 0.52 0.72 ( 18 , 21 , 22 ), AE: SMD= 0.14 0.24 0.31 ( 18 , 21 , 23 ), RE: SMD=0.22 0.29 0.39 ( 18 , 21 , 24 )). Hence, the choice of exercise modality constitutes a pivotal consideration for clinical professionals when devising exercise prescriptions aimed at preventing or mitigating cognitive decline ( 25 ).

Nonetheless, the absence of clinical studies concurrently comparing various types of exercise interventions, coupled with the scarcity of available direct evidence (head-to-head randomized clinical trials) within the literature incorporated in traditional pairwise meta-analyses, poses a formidable challenge in assessing the comparative efficacy of different exercise therapies. Therefore, the most efficacious exercise treatment modality for preventing or mitigating cognitive decline in SCD patients remains unclear at present. This ambiguity makes it challenging for healthcare professionals to draw definitive conclusions regarding the “most effective”exercise types and to formulate exercise intervention measures that are most effective in treating SCD patients.

Network Meta-Analysis (NMA) serves as a robust quantitative framework that amalgamates both direct and indirect evidence stemming from clinical trial networks ( 26 ). It facilitates the assessment of the effectiveness of different clinical interventions based on clinical evidence, effectively surmounting the limitations inherent in traditional meta-analyses ( 27 ). Furthermore, NMA also enables the ranking of intervention measures, yielding a hierarchy of all exercise therapies. Understanding which exercise selection is deemed the “most effective” can assist physicians in making clinical decisions, informing clinical practice, and integrating the optimal type of exercise into the patient’s rehabilitation objectives.

This systematic review was conducted following the PRISMA ( 28 ) and the PRISMA Extension Statement for Reporting of Systematic Reviews Incorporating Network Meta-analyses ( 29 ). The protocol for this study was registered with PROSPERO (registration number CRD42023289687).

Search strategy

Online databases for Web of Science, PubMed, Embase, Medline, Cochrane Library and PsycINFO were searched from inception to April 30, 2023. Referring to the study by Huang et al ( 30 ), the search strategy was initially devised for PubMed and subsequently adapted for other databases. The details of the retrieval strategy formulated for PubMed can be found in the appendix 1. The retrieval process was independently conducted by two researchers. In case of any disagreements, consensus was reached through discussions between the two researchers.

Study selection

The literature search records will be uploaded to Endnote X9, and a deduplication process will be conducted within the software. In the first stage, two researchers (BZ and JH) independently conducted a screening of the titles and abstracts of relevant articles, followed by a meticulous full-text assessment in strict accordance with the inclusion and exclusion criteria. Any discrepancies were resolved through consensus reached through discussions between the two researchers or, if necessary, adjudicated by a third researcher.

The detailed inclusion criteria as follows: (1) The study design must adhere to a randomized controlled trial (RCT) methodology. (2) The Participants must be diagnosed with SCD (meet the SCD conceptual framework proposed by Jessen et al. in 2014( 1 ) and China AD Preclinical Alliance( 11 )). (3) Intervention measures may encompass any form of exercise training. (4) The control group must fall into one of the following categories: standard care, health education, blank control (without administering any treatment or implementing any specific interventions) or treatment as usual. (5) The study must report at least one of the following outcomes: global cognitive function, memory function, executive function, attention, and verbal fluency. (6) The research must be documented in the English language. The SCD conceptual framework as follows: 1) subjective decline of memory rather than other domains of cognition; 2) onset of SCD within the last 5 years; 3) worries associated with SCD; and 4) worse self-perceived memory than others in the same age group; 5) absence of objective clinical impairment of MCI(the Mini-Mental State Examination (MMSE), the Montreal Cognitive Assessment (MoCA) or the modified Mini Mental Status examination (3MS) are within the normal range after years of education correction, and have not been clinically diagnosed as MCI as determined by clinical doctors).

The detailed exclusion criteria are as follows: 1) Studies specifically examining cognitive impairment in patients with various types of cancer, Parkinson’s disease, Huntington’s disease, epilepsy, multiple sclerosis, Psychiatric illnesses (e.g., major depression, schizophrenia and bipolar disorder) (these diseases, aside from being associated with cognitive dysfunction, typically exhibit diverse pathological changes; consequently, they may interfere the effects of exercise on cognitive function). 2) Significant cerebrovascular lesions (e.g., evident cerebral infarction or evident cerebral hemorrhage) ( 11 ). 3) Studies specifically investigating the effects of acute exercise (the effects generated after a single instance of acute exercise). 4) Comprehensive intervention measures in which exercise is not the primary component (e.g., exercise combined with cognitive training or exercise combined with physical therapy).

Outcomes: The core symptom of SCD is a decline in memory function ( 31 ), followed by impairments in executive function, attention and verbal fluency domains ( 32 ). Therefore, we used memory function as the primary outcome measure and analyzed executive function, attention, verbal fluency and global cognitive function as secondary outcome measures. The assessment scales with different outcome measures, arranged in order based on their frequency of use and psychometric characteristics, are listed sequentially in Appendix 2. When utilizing multiple instruments to assess a particular cognitive dimension, we select the most appropriate tool based on predefined criteria.

Data extraction

Two researchers (JF and HL) independently established data extraction forms according to the Cochrane Handbook’s guidelines ( 33 ), then proceeded to independently extract data, cross-referencing their findings. The extracted data encompassed general information (authors, publication year), participant characteristics (population, gender, average age), study features (number of patients, intervention measures, control measures, intervention duration, frequency, duration of each session), and outcomes (means, standard deviations (SDs), respective measurement tools). In instances where relevant statistical metrics were reported incompletely, we employed estimation methods for mean and SD based on sample size, median, range, and p-values, in accordance with the Cochrane Handbook guidelines ( 33 ). Additionally, we initiated email correspondence with the authors to procure any missing or incomplete data.

During the data extraction process, in order to assess the efficacy of various types of exercise interventions, we categorized exercise interventions following the American College of Sports Medicine Exercise Testing and Prescription Guidelines ( 20 ) and previous systematic reviews ( 34 , 35 ). These categories included Moderate-Intensity aerobic exercise (MI, such as walking, running, and cycling, etc), High-Intensity aerobic exercise (HI, such as Boxing and Track and Field, etc), Resistance exercise (RE, aimed at increasing muscle strength, e.g., using elastic tubes, elastic bands, and weight machines), Multicomponent exercise (ME, combining two or more types of exercise, such as MI combine RE and balance training) and Mind-body exercise (MBE, emphasizing the integration of movement with breathing, mindfulness and memory, including practices like baduanjin, yoga, and mind-motor exercise). To investigate the moderating variables of exercise effects, we categorized and coded exercise frequency, intensity, duration per session, and intervention duration (Appendix 3).

Risk of bias assessment

Two researchers (MZ and JH) independently conducted methodological quality assessments of the included RCTs using the “Cochrane Risk of Bias Assessment Tool, 2nd Edition” (RoB 2) ( 36 ). Divergences were resolved through consensus discussions, and in cases where differences couldn’t be reconciled, consultation with a senior researcher was sought. Studies were categorized into low, high, or some concerns of bias based on the following criteria: Randomization process; Deviations from intended interventions; Missing outcome data; Measurement of the outcome; Selection of the reported result.

Data synthesis and statistical analysis

Pairwise meta-analyses.

We utilized the “meta-analysis” module in Stata 14.0 (Verson 14.0; StataCorp, College Station, TX, USA) to perform pairwise analyses for all direct comparisons, thereby elucidating the effects of various exercise interventions compared to the control group individually. Depending on the magnitude of heterogeneity in the data, we employed the random-effects model (I-V heterogeneity method) or the fixed-effects model (inverse variance method) to calculate the standardized mean difference (SMD) and its corresponding 95% confidence interval (95% CI) for the differences in scores before and after the intervention. Using the I 2 statistic to estimate the proportion of total variance attributed to heterogeneity between studies in each pairwise comparison.

Network meta-analysis

Network meta-analyses (NMA) were conducted using the “mvmeta” ( 37 , 38 ) and “network” ( 39 , 40 ) packages in Stata 14.0 (Verson 14.0; StataCorp, College Station, TX, USA), based on a frequentist analysis framework, for both primary and secondary outcome measures. NMA integrates the results from individual studies, and each treatment effect of the intervention/control group can be obtained through direct or indirect comparison ( 41 , 42 ). When there is no direct connection between two treatment arms, the results are based on indirect evidence ( 41 , 42 ). To visualize the network geometry and connectivity of nodes, we created network diagrams for each cognitive outcome measure. Each node represents an intervention, and the connecting lines between two nodes represent one or more direct comparisons ( 43 ). The size of each node is proportional to the number of participants receiving that intervention, with larger nodes indicating a higher number of participants who received the intervention ( 43 ). The thickness of the connecting lines is related to the number of studies that directly compared these two interventions, with thicker lines representing a greater number of studies ( 43 ).

We initially employ an inconsistency model for global inconsistency analysis. A p-value below 0.05 in the inconsistency test indicates the presence of global inconsistency ( 44 ). The local inconsistency analysis was conducted using the node-splitting method. The presence of local incongruity is signified when the p-value of the incongruity test falls below 0.05 ( 44 ). When evidence closed loops are present in the network diagram, we use the loop-specific method for loop inconsistency analysis. When the incongruity factor approaches zero, it signifies the concordance between two sources of evidence ( 44 ).

Fitting with multivariate random-effects (restricted maximum likelihood estimation) meta-analysis model in the framework of frequentism. This model takes into consideration the heterogeneity between studies caused by clinical and other factors, providing more conservative confidence intervals (CI) for the combined point estimates, in order to account for the interrelation of effect sizes among trials involving more than two groups ( 44 , 45 ). After combining direct and/or indirect comparisons for any pair of interventions, we computed pooled effect sizes represented as SMDs with corresponding 95% CIs. The effect sizes were categorized as small (SMD <0.40), moderate (0.40 ≤ SMD ≤ 0.70), or large (SMD >0.70) following the Cochrane handbook guidelines( 33 ).

To rank exercise interventions, we utilized a parameter-guided bootstrapping procedure with 10,000 resamples to assess the effectiveness of each intervention and calculated the Surface Under the Cumulative Ranking curve (SUCRA) values. SUCRA is a precise estimation of the cumulative ranking probability for the top i treatments. For each treatment j among the n compared treatments, the cumulative probability of treatment j being ranked within the top i is calculated using the following formula: \(\text{SUCRA}_{j}=(\sum\nolimits_{\rm{i}=1}^{\rm{n}-1}\ cum_{j,i})/(\rm{n}-1)\) ( 46 ). The range of SUCRA values spans from 0% to 100%, and the closer the value approaches 100%, the higher the likelihood that the intervention is more effective.

Regression and sensitivity analysis

To further explore the sources of heterogeneity and inconsistency, we conducted a Meta-regression analysis on the primary outcome measures, using the frequency, intensity, duration, and duration of exercise interventions as covariates.

A sensitivity analysis was conducted by excluding RCTs with at least one domain assessed as high risk of bias in pairwise meta-analyses, aiming to explore the robustness of the study outcomes.

Small study effects

Egger’s test was employed to assess the presence of small study effects. Additionally, funnel plots were generated for visual inspection of publication bias for each comparison of outcomes ( 47 ).

Literature search and selection

After deduplication, a total of 1316 records were identified. Among these records, 58 were considered potentially relevant following the initial screening of titles and abstracts. Following the application of inclusion and exclusion criteria, a total of 11 randomized controlled trials, comprising 1166 participants, were included in the network meta-analysis (Fig 1 ). The appendix 4 provide detailed characteristics of the studies included in the analysis, and the appendix 5 contain all citations of the studies included in the NMA.

Flow of studies in the review

Note: RCT: Randomized controlled trial, NC: Normal cognitive, SCD: Subjective cognitive decline, MCI: Mild cognitive impairment, AD: Alzheimer’s disease.

Characteristics of included studies

Among the included studies, the sample sizes ranged from 31 to 415, with a mean age of 62.87 years. Eight studies (1079 participants) investigated the impact of exercise on memory function ( 48 – 55 ), eight studies (921 participants) examined the influence of exercise on executive function ( 48 , 49 , 51 – 54 , 56 , 57 ), while three studies (573 participants) explored the effects of exercise on attention ( 48 , 51 , 53 ), three studies (610 participants) investigated the influence of exercise on verbal fluency ( 49 , 53 , 58 ), and six studies (729 participants) assessed the impact of exercise on global cognitive function ( 48 , 49 , 52 , 53 , 56 , 57 ). There are a total of five intervention categories, which include Moderate-Intensity aerobic exercise (MI, N = 8) ( 49 – 53 , 55 , 57 , 58 ), High-Intensity aerobic exercise (HI, N = 2) ( 52 , 56 ), Resistance exercise (RE, N = 2) ( 48 , 53 ), Multicomponent exercise (ME, N = 3) ( 50 , 53 , 56 ), and Mind-body exercise (MBE, N = 3) ( 52 , 54 , 58 ) (Appendix 4, Appendix 5).

Risk of bias

The summary of bias risk can be found in the supplementary materials. All included studies were RCTs, but 31% of the trials did not adequately report the implementation methods of randomization. Out of the 11 trials, 6 trials (54.5%) were rated as having a low risk of bias. For these 6 trials, a significant proportion of “Some concerns” (36.4%) arose due to the lack of detailed descriptions regarding group concealment or the handling of missing outcome data. One trial (9.1%) received a high risk of bias assessment due to the absence of researcher blinding (Appendix 6).

Appendix 7 presents the outcomes of pairwise meta-analysis and estimates of heterogeneity. In brief, exercise interventions were found to be more efficacious than control groups in the domains of memory (Combine SMD=0.20, 95 % CI: 0.07∼0.34, I 2 =33.8%), executive function (−0.15, 95 % CI: −0.29 ∼ −0.01, I 2 =25.0%), and verbal fluency (−0.21, 95%CI: −0.35 ∼ −0.06, I 2 =9.3 %) in SCD. Nevertheless, exercise interventions did not exhibit significant differences in improving global cognitive function ( P =0.72, I 2 =0.0%) and attention ( P =0.88, I 2 =0.0%) in SCD compared to the control groups.

A total of five different interventions and control arms were included, comprising 1166 patients with SCD in our network meta-analysis. The inconsistency test based on network analysis showed no statistically significant differences in global inconsistency (memory: P =0.07, executive function: P =0.39, verbal fluency: P =0.10, attention: P =0.61, global cognitive function: P =0.22), detailed results are provided in the appendix 8. When evaluating closed-loop networks, no statistically significant differences in inconsistency between direct and indirect outcomes were observed. Detailed results can be found in the appendix 8. The network diagram (Fig 2 ) displays the weights of all available comparisons included in this network meta-analysis. Comparative effects between exercise interventions can be found in the league table (Fig 3 ). Cumulative probability plots for different exercise interventions and the ranking of SUCRAs are presented in Fig 4 and Table 1 , respectively.

Network plot of available treatment comparisons

Note: Each node represents an intervention, and the connecting lines between two nodes represent one or more direct comparisons. The size of each node is weighted based on the number of participants receiving that intervention, while the thickness of the connecting lines is weighted based on the number of studies directly comparing those two interventions. A: memory, B: executive function, C: verbal fluency, D: attention, E: global cognitive function. MI aerobic exercise: Moderate-Intensity aerobic exercise, HI aerobic exercise: High-Intensity aerobic exercise.

Network meta-analysis of effectiveness comparison

Note: Each cell displays the SMD with a 95% confidence interval. For any cell, a negative SMD favors interventions in the upper-left corner, while a positive SMD favors interventions in the lower-right corner. Significant results are highlighted in bold. MI: Moderate-Intensity aerobic exercise, HI: High -Intensity aerobic exercise, RE: Resistance exercise, ME: Multicomponent exercise, MBE: Mind-body exercise.

Cumulative ranking probability plot

Note: A: memory, B: executive function, C: verbal fluency, D: attention, E: global cognitive function. MI aerobic exercise: Moderate-Intensity aerobic exercise, HI aerobic exercise: High-Intensity aerobic exercise.

The network meta-analysis results indicate a significant impact of mind-body exercise on memory function in SCD patients when compared to the control group (combined SMD: 0.58, 95%CI: 0.06 ∼ 1.10). There were no significant differences between different types of exercises. Mind-body exercise (MBE) had the highest probability (70.6%) of being the most effective exercise modality, with a SUCRA value of 90.4. Followed by multicomponent exercise (ME, SUCRA=68.5, P=17.3%), moderate-intensity aerobic exercise (MI, SUCRA=47.1, P=7.8%), resistance exercise (RE, SUCRA=37.3, P=3.4%), and high-intensity aerobic exercise (HI, SUCRA=37.3, P=0.8%). Refer to Fig 3 , Fig 4 and table 1 for details.

For executive function in SCD patients, MBE (combined SMD: 0.41, 95%CI: 0.09 ∼ 0.73) and moderate-intensity aerobic exercise (combined SMD: 0.23, 95%CI: 0.03 ∼ 0.43) demonstrated significantly greater improvements compared to the control group. Furthermore, mind-body exercise significantly outperformed resistance exercise in improving executive function (combined SMD: 0.38, 95%CI: 0.01 ∼ 0.75). MBE has the highest probability (74.0%) of being the most effective exercise type for preserving executive function, with a SUCRA value of 91.8. Following that are MI (SUCRA=68.2, P=19.7%), HI (SUCRA=67.1, P=4.9%), ME (SUCRA=33.8, P=1%), and RE (SUCRA=23.5, P=0.4%).

Refer to Fig 3 , Fig 4 and table 1 for details.

However, we did not observe significant differences between different types of exercise interventions compared to the control group or in comparisons between different types of exercise interventions in the remaining cognitive dimensions. Network plots, cumulative ranking plots, and SUCRA values for exercise interventions in the remaining cognitive dimensions are presented in Fig 2 , Fig 3 , Fig 4 , as well as Appendix 8.

Meta-regression analyses were separately conducted for different types of exercise interventions (primarily focusing on the main outcome measure: memory), with exercise intervention frequency, intensity, duration per session, and intervention duration were included as covariates. The results show that the intensity of each session serves as a moderating factor affecting the effectiveness of exercise interventions on memory in individuals with SCD (see the appendix 9 for details).

We excluded the study ( 56 ) with a high risk of bias in at least one domain, which encompassed cognitive domains such as global cognitive function and executive function. Sensitivity analysis revealed that the outcomes of the interventions remained unchanged (see the appendix 10 for details).

Overall, we did not find compelling evidence of small study effects among the outcomes. The points on the funnel plots for each study domain are visually symmetrically distributed around the mean estimated treatment effect (see the appendix 11 for details). The p-values for Egger’s test were as follows: 0.39 for memory, 0.84 for executive function, 0.14 for verbal fluency, 0.87 for attention, and 0.36 for global cognition (see the appendix 11 for details).

This systematic review and network meta-analysis on exercise interventions for patients with Subjective Cognitive Decline (SCD) included data from 11 clinical trials involving a total of 1166 participants. To our knowledge, this review is the first network meta-analysis aimed at exploring the relative efficacy of different types of exercise on cognitive function in SCD. Our study results corroborate the beneficial impact of exercise interventions on cognitive function in SCD and highlight Mind-Body Exercise (MBE) as the most promising exercise therapy for attenuating memory and executive function decline in SCD patients.

Over the past few decades, the beneficial effects of MBE on cognitive function have gradually become a research focus. MBE represents a multimodal form of exercise that emphasizes the harmonious integration of mind, body, and spirit ( 59 ). In addition to aiding in balance control, flexibility, and muscle strength, MBE also places emphasis on mental focus, procedural memory, physical equilibrium, and relaxation ( 60 ). Compared to aerobic and resistance exercises that focus primarily on cardiovascular fitness and strength, MBE integrate movement sequences with breath control and attention regulation. Additionally, they have been shown to increase oxygenated hemoglobin levels in the prefrontal cortex ( 61 ). The combination of these physical and neural resources can offer an explanation for the observed differences in the effects of exercise therapy.

Furthermore, the combined nature of ME involving two or more modalities presents challenges in ensuring that each exercise component meets optimal durations, frequencies, and intensities during training. This can lead to a diminished practical efficacy of ME in real-world applications. It is worth noting that we observed exercise intensity as a moderating variable influencing the magnitude of exercise effects, with very high-intensity exercise not necessarily resulting in improved memory function for SCD individuals. MBE typically involves slow-paced and low-intensity activities, making it a more suitable option for older adults compared to other forms of exercise ( 62 , 63 ). This may potentially serve as another explanation for why MBE demonstrates the greatest potential in mitigating cognitive decline in SCD. Researchers should also take these factors into consideration in future studies.

Recent research findings have supported the potential relationship between physical activity and neural changes, indicating that MBE can modulate brain structures ( 64 ) and induce alterations in brain neural activity and functional connectivity ( 64 , 65 ), including regions such as the hippocampus ( 66 ) and prefrontal cortex ( 64 ), which play a crucial role in cognitive function. Currently, consistent observations indicate reduced structural integrity in the hippocampus and prefrontal gray matter in individuals with SCD ( 67 – 70 ), as well as a decrease in the functional connectivity between the hippocampus and prefrontal regions ( 71 , 72 ). The hippocampus and prefrontal cortex are the core regions responsible for memory and executive function processes, respectively ( 73 , 74 ). The modulation of brain structure, neural activity, and functional connectivity by MBE may serve as the foundation for the beneficial effects of such exercise on memory and executive function in SCD.

MBE is also highly likely to synergize its benefits in enhancing memory and executive function through other neurobiological mechanisms that may initiate favorable biochemical alterations. For instance, MBE may enhance cognitive function by upregulating levels of brain-derived neurotrophic factor (BDNF) in the plasma, which is a crucial mediator of central nervous system neuroplasticity ( 75 ). Additionally, it may also exert beneficial effects on the brain and cognition by modulating inflammatory cytokines (levels of which are associated with cognitive impairment ( 76 – 78 )) such as tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), IL-10, and IL-1β, with studies ( 79 – 81 ) reporting that, levels of inflammatory cytokines are associated with cognitive impairment. These mechanisms contribute to its potential to enhance cognitive function. Overall, our research findings suggest that MBE may have unexpected benefits for memory and executive function in SCD patients, consistent with previous meta-analytic ( 82 ) results.

For executive function, while the efficacy is lower compared to MBE, we also observed a facilitative effect on executive function from moderate-intensity aerobic exercise (MI). Prior research ( 83 ) has indicated that executive function is the cognitive domain most sensitive to the beneficial effects of aerobic exercise. Potential underlying mechanisms may involve aerobic exercise’s modulation of cerebral vascular health, enhancement of cerebral blood flow, and regional cortical thickness, which induce cortical activation in the prefrontal subregions ( 84 – 86 ). In previous research ( 87 – 89 ), it has been observed that the intensity of aerobic exercise selectively impacts executive function, with high-intensity aerobic exercise appearing to have less pronounced effects on the improvement of executive function, which aligns with our findings. They propose that the positive impact of aerobic exercise on executive function follows an inverted U-shaped curve, increasing from no intensity to moderate intensity and then declining with further increases in intensity ( 87 – 89 ). Additionally, the release of various neurochemical substances related to cognitive function (e.g., catecholamines, cortisol, BDNF) induced by exercise also depends on factors such as exercise intensity ( 90 ).

Consistent with the study by Coelho et al. ( 91 ), we cannot provide evidence suggesting a significant enhancement of executive function in SCD through combined exercise. This may be related to the substantial disparities in exercise intensity and frequency used in some studies compared to the activity standards recommended for older adults. The American College of Sports Medicine ( 20 ) recommends that older adults should engage in at least 5 days of moderate-intensity exercise for 30–60 minutes per day each week. However, within the articles included in this meta-analysis, the highest intervention frequency observed for studies focusing on executive function was 3 times, and it only involved one study ( 52 ). The insufficient exercise dosage may potentially attenuate the positive effects of ME.

It is noteworthy that within our network meta-analysis, no significant efficacy of exercise on attention, verbal fluency, and global cognitive function in individuals with SCD was observed. In the preclinical stage of Alzheimer’s disease, SCD typically exhibits the earliest cognitive impairment in the domain of memory, followed by executive functions ( 92 ). We speculate that the relatively limited effects of exercise on attention and verbal fluency cognitive functions may be attributed to the less severe impairment of these cognitive domains in individuals with SCD. However, Venegas-Sanabria et al. ( 93 ), when assessing the impact of exercise on individuals with Alzheimer’s disease or mild cognitive impairment, also found that exercise did not yield significant beneficial effects on verbal fluency and attention. The emergence of such results may be related to the insensitivity of the domains of attention and language fluency to exercise, as cognitive domains exhibit varying levels of sensitivity to exercise (e.g., aerobic exercise having the most pronounced therapeutic effect on executive functions ( 83 )). Interestingly, in our conventional pairwise meta-analysis, we observed a positive effect of exercise on verbal fluency in SCD. However, this finding was based on the inclusion of only one study ( 53 ). Given the limited number of clinical trials within the studies included in the analysis that have investigated the impact of exercise on attention and verbal fluency in SCD, the findings warrant cautious interpretation and necessitate further experiments in the future to augment the required evidence.

In addition, one of the diagnostic criteria for SCD is the absence of objectively demonstrable clinical impairment associated with MCI. Based on this diagnostic criterion, the neurobehavioral scores for global cognitive function in the SCD patients included in the analysis were within the normal range, and baseline data demonstrated preserved cognitive performance. This suggests that there is only minimal decline in global cognitive function, leaving limited room for exercise to improve global cognitive function in SCD. It has been reported that exercise interventions require a sufficiently long duration to exert an impact on specific cognitive domains ( 94 , 95 ). The majority of studies included in the analysis had a duration of 6 months or less, which impedes the long-term investigation of exercise effects on attention, verbal fluency, and global cognitive function in SCD. As for the mechanisms involved in this, more clinical trials are needed to fill this gap.

We anticipate that our research findings will hold significant implications for both clinical decision-making and scientific investigation. In the context of clinical rehabilitation, MBE deserves heightened attention and can be recommended as an adjunct therapy for SCD patients due to its significant benefits in improving memory and executive function. MI can also be considered as a routine non-pharmacological treatment for SCD patients to enhance their executive function. Certainly, future clinical trials should undertake more investigations into elucidating the mechanisms by which exercise influences SCD cognitive functions to explain the reasons behind the benefits it confers. For clinical researchers, regular updates to NMAs on this topic are indispensable as new data continues to emerge.

While our meta-analysis demonstrated the beneficial impact of exercise on SCD cognition, there are still some limitations to consider. Firstly, the number of studies included in our review was limited, and to validate our findings, large-scale trials will be needed in the future. Secondly, only a small number of studies have reported long-term follow-up data after the conclusion of interventions. Consequently, we extracted data only from the included studies for the period after the interventions were completed, resulting the sustained benefits of exercise on various aspects of SCD cognition unverified. Furthermore, among the included studies, only one study ( 53 ) employed a multi-arm design, directly comparing the effects of different types of exercise on SCD cognition. Many effect size estimates were reliant on indirect comparisons. Considering that evidence from direct comparisons is more robust than indirect comparisons, it is imperative to conduct more multi-arm designed studies in the future.

Our NMA also has other limitations, such as a lack of exploration into the most effective exercise dosages (intensity, frequency, session duration, and length of intervention). This is another critical factor influencing rehabilitation outcomes. The dose-response relationship of exercise interventions on SCD cognitive function needs further investigation. In addition, due to the unavailability of complete data, we did not conduct subgroup analysis. Future research endeavors may explore whether different forms of exercise are beneficial for distinct types of SCD (e.g., the impact of aerobic or resistance exercise on cognitive function in SCD with cardiovascular risk). This would be an intriguing topic, as research ( 96 ) suggests a novel direction in dementia prevention by offering diverse intervention measures tailored to individual prevention needs, varying with lifestyle factors and identified risks of cognitive decline. Lastly, our NMA only included articles written in English, which could potentially result in the omission of information from eligible research reports conducted in other languages.

This network meta-analysis has synthesized the existing evidence from clinical studies, offering clinical professionals and researchers some important findings regarding exercise therapy. Our research reveals that among individuals experiencing SCD, MBE emerges as the most effective exercise modality in slowing down the decline in memory and executive function. Additionally, MI demonstrates a favorable capacity for improving executive function in SCD patients. Nevertheless, in light of the limitations of our aforementioned meta-analysis and the paucity of studies in the current literature, the results should be interpreted with caution. To bolster the findings of this NMA, further investigation is warranted, including well-designed, large-scale, multi-arm, multicenter trials.

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Livingston G, Huntley J, Sommerlad A, et al. Dementia Prevention, Intervention, and Care: 2020 Report of the Lancet Commission. Lancet, 2020, 396(10248): 413–46. https://doi.org/10.1016/s0140-6736(20)30367-6

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Acknowledgments

We extend our gratitude to the authors of the original manuscripts for providing the requisite data for this network meta-analysis.

Funding: This research was supported by the Project of Administration of Traditional Chinese Medicine of Guangdong Province, China [grant numbers 20201066]; Guangdong Basic and Applied Basic Research Foundation, China [grant number 2021A1515010135]; and the IIT Research Project of The Fifth Affiliated Hospital of Sun Yat-sen University [YNZZ 2021-09.

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R. Chen, J. Huang, M. Zhang, Y. Wang, J. Fu, H. Liang & Hongrui Zhan

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Authors’ contributions: HZ conceived and oversaw this study. BZ and JH made significant contributions to the literature search and screening. MZ and YW provided substantial contributions to bias risk assessment. JF and HL performed data extraction and conducted cross-verification. RC analyzed and interpreted the extracted data and drafted the initial version of the manuscript. All listed authors meet the authorship eligibility criteria, and no additional eligible authors have been omitted. Furthermore, all authors have reviewed and approved the final version of the manuscript and have reached a consensus on the order of authorship.

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Chen, R., Zhao, B., Huang, J. et al. The Effects of Different Exercise Interventions on Patients with Subjective Cognitive Decline: A Systematic Review and Network Meta-Analysis. J Prev Alzheimers Dis (2024). https://doi.org/10.14283/jpad.2024.65

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Wall Street Journal Marks One Year Since Evan Gershkovich’s Arrest in Russia

Journalism is not a crime..

Julianne McShane

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Wall Street Journal reporter Evan Gershkovich stands in a glass cage in a courtroom at the Moscow City Court, in Moscow, Russia, on April 18, 2023. Alexander Zemlianichenko/AP

Today marks one year since Wall Street Journal reporter Evan Gershkovich was arrested in Russia on what American officials say are false charges of espionage. He has been held in jail ever since.

Members of Russia’s Federal Security Service—the country’s intelligence agency, also known as the FSB—detained Gershkovich while he was on a reporting assignment in the city of Yekaterinburg,  according to the Journal . Gershkovich had deep familiarity the country: his parents fled the Soviet Union in the 1970s. He had full press credentials from Russia’s foreign ministry and had reported from Moscow for Agence France Press and the Moscow Times before joining the Journal in January 2022. Russia has not publicly presented evidence of its espionage claims against Gershkovich, the Journal reports. 

Since his arrest—which marks the first time an American journalist has been held on such charges in Russia since the end of the Cold War—Gershkovich has been in Russia’s notorious Lefortovo prison, where he spends 90 percent of his day in a small cell, according to the paper. Earlier this week, a Russian court extended Gershkovich’s pre-trial detention by three months, until June 30. The Committee to Protect Journalists condemned the extension, calling it “another cynical affront to press freedom by the Russian authorities.” 

In a letter published today, Journal editor-in-chief Emma Tucker  called Gershkovich’s detention “a blatant attack on the rights of the free press,” adding that “given the lessons of history and the arbitrary power of the Russian state, if there is a trial, we would expect a guilty verdict—something we would view as a travesty of justice.” A conviction could carry a sentence of 10 to 20 years, the Journal reports .

Roger Carstens, the Biden administration’s special envoy for hostage affairs, told the New York Times that the US government is involved in “intensive efforts” to secure the releases of Gershkovich and ex-Marine Paul Whelan, who has been in Russian  custody since 2018 and was sentenced to 16 years in prison on espionage charges, which American officials also deny .

The Journal dedicated its front page to Gershkovich today, leaving much of it blank under the headline, “His story should be here,” alongside other stories on his detention  and the threats authoritarians pose to journalists around the world. (More than 520 journalists are imprisoned worldwide, according to the group Reporters Without Borders.)

Here is an early look at the front page of a special section wrapping today's Wall Street Journal https://t.co/kTxN0a0m6N pic.twitter.com/X8C54alCiH — The Wall Street Journal (@WSJ) March 29, 2024

The Journal also hosted a public, 24-hour read-a-thon, which streamed live on social media, of Gershkovich’s work, with participants such as NBC’s Lester Holt and Andrea Mitchell, ABC’s David Muir, and CNN’s Jake Tapper and Kaitlan Collins.

In a statement released today, President Joe Biden said he will “never give up hope” of freeing Gershkovich.

“We will continue working every day to secure his release,” Biden said. “We will continue to denounce and impose costs for Russia’s appalling attempts to use Americans as bargaining chips. And we will continue to stand strong against all those who seek to attack the press or target journalists—the pillars of free society.”

Secretary of State Antony Blinken also acknowledged the anniversary of Gershkovich’s arrest, noting that “Russia has provided no evidence of wrongdoing for a simple reason: Evan did nothing wrong. Journalism is not a crime.” 

Gershkovich’s parents have said “he’s doing the best he can under the circumstances, and the circumstances are very hard.” The reporter sends his parents letters weekly, his mother, Ella Milman, added in an interview with Tucker in January. They told the  Times he also plays chess with his father over email and reads books recommended by friends.

In the meantime, we’ll echo something you’ll probably hear a lot of today: Journalism is not a crime. 

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1. Introduction

2. observations and detection, 3. association with the coma cluster, 4. analysis, 5. discussion, acknowledgments.

• Appendix A:
• List of figures

A giant thin stellar stream in the Coma Galaxy Cluster

Javier Román 1 ,2 ,3 , Robert Michael Rich 4 , Niusha Ahvazi 5 ,6 , Laura V. Sales 5 , Chester Li 4 ,7 , Giulia Golini 2 ,3 , Ignacio Trujillo 2 ,3 , Johan H. Knapen 2 ,3 , Reynier F. Peletier 1 and Pablo M. Sánchez-Alarcón 2 ,3

1 Kapteyn Astronomical Institute, University of Groningen, PO Box 800 9700 AV Groningen, The Netherlands e-mail: [email protected] 2 Instituto de Astrofísica de Canarias, c/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain 3 Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain 4 Department of Physics & Astronomy, University of California Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095-1547, USA 5 Department of Physics and Astronomy, University of California, Riverside, 900 University Avenue, Riverside, CA 92521, USA 6 Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101, USA 7 Department of Astronomy, University of Washington, 3910 15th Avenue, NE, Seattle, WA 98195, USA

Received: 30 April 2023 Accepted: 13 October 2023

The study of dynamically cold stellar streams reveals information about the gravitational potential where they reside and provides important constraints on the properties of dark matter. However, the intrinsic faintness of these streams makes their detection beyond Local environments highly challenging. Here, we report the detection of an extremely faint stellar stream ( μ g , max = 29.5 mag arcsec −2 ) with an extraordinarily coherent and thin morphology in the Coma Galaxy Cluster. This Giant Coma Stream spans ∼510 kpc in length and appears as a free-floating structure located at a projected distance of 0.8 Mpc from the center of Coma. We do not identify any potential galaxy remnant or core, and the stream structure appears featureless in our data. We interpret the Giant Coma Stream as being a recently accreted, tidally disrupting passive dwarf. Using the Illustris-TNG50 simulation, we identify a case with similar characteristics, showing that, although rare, these types of streams are predicted to exist in Λ-CDM. Our work unveils the presence of free-floating, extremely faint and thin stellar streams in galaxy clusters, widening the environmental context in which these objects are found ahead of their promising future application in the study of the properties of dark matter.

Key words: galaxies: clusters: individual: Coma / galaxies: evolution / galaxies: interactions / galaxies: photometry

© The Authors 2023

This article is published in open access under the Subscribe to Open model . Subscribe to A&A to support open access publication.

Extremely low-surface-brightness features in the form of stellar streams and haloes provide crucial information for understanding the hierarchical model of galaxy evolution in a Λ-CDM framework ( Bullock & Johnston 2005 ; Johnston et al. 2008 ; Cooper et al. 2010 ; Pillepich et al. 2014 ; Monachesi et al. 2019 ; Rey & Starkenburg 2022 ; Genina et al. 2023 ). These structures are created from the continuous accretion of satellites, and representative examples are found in the environments of the Local Group (e.g., Belokurov et al. 2006 ; McConnachie et al. 2018 ; Ibata et al. 2021 ; Dodd et al. 2023 ) and of nearby galaxies (e.g., Mouhcine et al. 2010 ; Crnojević et al. 2016 ) by counting individual stars.

The availability of high-precision stellar positions and velocities – mainly in the Milky Way environment – has promoted intense research in this field (see a review by Helmi 2020 ). One of the applications of the study of stellar streams, given their extremely low stellar density, is their ability to reveal the gravitational potential in which they reside (e.g., Johnston et al. 1999 ; Dubinski et al. 1999 ; Sanders & Binney 2013 ; Reino et al. 2021 ; Pearson et al. 2022 ), especially for the case of cold stellar streams ( Bonaca & Hogg 2018 ). Because of their coherent stellar motion, any nearby perturbation by a conspicuous low-mass potential can be identified in parameter space (e.g., Ibata et al. 2002 ; Carlberg 2012 ; Erkal & Belokurov 2015 ). This is particularly interesting for the case of a potential perturbation by dark matter subhaloes, which could provide relevant information about the properties of dark matter in already known streams in the Milky Way such as Pal 5 or GD-1 ( Erkal et al. 2016 ; Banik & Bovy 2019 ; Ibata et al. 2020 ; Banik et al. 2021 ).

Because of the large amount of information contained in stellar streams, there have been sustained efforts to explore these structures in external galaxies in order to obtain a larger environmental and statistical context ( Tal et al. 2009 ; Martínez-Delgado et al. 2010 ; Rich et al. 2012 ; Duc et al. 2015 ; Trujillo et al. 2021 ; Martínez-Delgado et al. 2023a ). However, resolving individual stars is only feasible out to a few megaparsecs, and the significant observational challenges of large-area, low-surface-brightness photometry ( Knapen & Trujillo 2017 ; Mihos 2019 ) mean that the very low-surface-brightness regimes at which cold stellar streams have been identified in the Milky Way are mostly unexplored at greater distances, and most of the expected faint stellar streams remain undetected ( Martin et al. 2022 ).

With the imminent arrival of the new generation of instrumentation and deep optical surveys such as Euclid ( Euclid Collaboration 2022a ), the Rubin Observatory (Ivezić et al. 2019), and the Nancy Grace Roman Space Telescope ( Akeson et al. 2019 ), along with significant technical efforts ( Euclid Collaboration 2022b ; Smirnov et al. 2023 ; Kelvin et al. 2023 ), it is expected that the attainable surface-brightness limits will increase the number of stellar streams detected in external galaxies by orders of magnitude ( Pearson et al. 2019 ). This will provide a broader environmental context and a greater understanding of the processes involved, yielding invaluable information in both galactic evolution models and near-field cosmology.

We present the first results of an extensive observational campaign to explore the Coma cluster at the ultralow-surface-brightness regime: the HERON Coma Cluster Project. The Coma cluster is one of the most-studied extragalactic objects, and is of particular historical significance (see a historical review by Biviano 1998 ), for example being the site of the discovery of first evidence of dark matter ( Zwicky 1933 ) or intracluster-light ( Zwicky 1951 ). The existence of galactic debris in Coma ( Trentham & Mobasher 1998 ; Gregg & West 1998 ) and other clusters ( Conselice & Gallagher 1999 ; Calcáneo-Roldán et al. 2000 ; Mihos et al. 2017 ) is direct evidence of the processes of galactic cannibalism and accretion giving rise to the building of the intragroup and intracluster light haloes ( Rudick et al. 2009 ; DeMaio et al. 2015 ; Montes 2022 ). As Coma is one of the most massive local clusters with intense merger activity (e.g., Jiménez-Teja et al. 2019 ; Gu et al. 2020 ), it is an ideal setting for carrying out an exploration of this type of structure, providing crucial information on the environmental and interaction processes taking place in clusters.

Here, we report the discovery of the Giant Coma Stream, an extremely faint, thin, and free-floating stellar stream in the outskirts of the Coma galaxy cluster. At 510 kpc in length, it is several times longer than the two previously identified stellar streams in the Coma cluster ( Trentham & Mobasher 1998 ; Gregg & West 1998 ) or other clusters ( Conselice & Gallagher 1999 ; Calcáneo-Roldán et al. 2000 ; Mihos et al. 2017 ), while showing orders-of-magnitude lower surface brightness and total mass. We show that this new stream is consistent with features found in numerical simulations of hierarchical cluster formation (Illustris TNG). We assume a distance of 100 Mpc for Coma ( Liu & Graham 2001 ), corresponding to a distance modulus of m  −  M = 35.0 mag and a spatial scale of 0.462 kpc arcsec −1 using cosmological parameters from Planck Collaboration VI (2020) . We use the AB photometric system throughout this work.

2.1. HERON data

We carried out an extensive observational campaign of deep observations in the Coma Cluster in g and r bands with the 0.7 m Jeanne Rich Telescope. This telescope is mainly dedicated to the Halos and Environments of Nearby Galaxies (HERON) Survey ( Rich et al. 2019 ), and is designed to be particularly efficient in the low-surface-brightness regime. It has a single Finger Lakes Instruments ML09000 detector with 3048 2 12 μm pixels with a scale of 1.114 arcsec pix −1 , allowing a 57 × 57 arcmin field of view. A thorough technical description of the instrumentation is provided by Rich et al. (2017) . Observations in this work are part of the HERON Coma Cluster Project (Román et al., in prep.), the goal of which is to carry out a study of the diffuse light of the Coma cluster to unprecedented limits in surface brightness.

Observations were conducted in the spring and summer of 2019 for the g band and 2020 for the r band. A total of 461 and 579 exposures of 300 s were taken in the g and r bands, respectively. Observational conditions were mostly dark. Dithering steps of tens of arcminutes were performed with the aim of covering an area of 1.5 × 1.5° centered on Coma. The data reduction was performed by standard subtraction of combined superbias and superdarks for each night from the science images. Flat fields were constructed by combining and normalizing the heavily masked bias-subtracted and dark-subtracted science images. Astrometry was performed on all images individually with the Astrometry.net software package ( Lang et al. 2010 ) and SCAMP ( Bertin 2006 ). The images were then reprojected onto a common astrometrical grid with SWARP ( Bertin et al. 2002 ) and photometrically calibrated with the Dark Energy Camera Legacy Survey (DECaLS; Dey et al. 2019 ) as a reference. The images were combined with a very conservative sky fitting based on Zernike polynomials to preserve the information at low surface brightness. We used orders between 1 and 4 depending on the degree of gradients in the images, always using the lowest possible order able to fit the gradients of each individual image.

The total exposure time was 38.4 h and 48.25 h in the g and r bands, respectively. The maximum surface brightness limits in these data are 30.1 and 29.8 mag arcsec −2 [3 σ , 10″ × 10″] in both g and r bands (see definition by Román et al. 2020 ). In the region of interest here, the surface brightness limits reach 29.5 mag arcsec −2 [3 σ , 10″ × 10″] in both g and r bands. The seeing conditions were not restrictive as we were interested in the diffuse light, producing a final seeing of approximately 3 arcsec in both g and r bands. Further details about this project and data will be provided in an upcoming publication.

A preliminary visual analysis of these data allowed us to identify an extremely faint feature with very thin morphology (see Fig. 1 a). Its detected length and width are approximately 18.5 and 1 arcmin, respectively.

2.2. WHT data

To obtain confirmation of this feature, we carried out follow-up observations with the 4.2 m William Herschel Telescope. We used the PF-QHY Camera with a field of view of 7.1′×10.7′ and pixel scale of 0.2667 arcsec pix −1 . We used an L luminance filter, which is a UV-IR blocker with a high efficiency of 95% in the range of 370−720 nm, thus covering the g and r SDSS filters. The purpose of using a wide luminance band is to achieve maximum detection power given the extremely low surface brightness of this feature. A total of 200 individual 180 s exposures were obtained on June 4, 6, 11, and 14, 2021, under seeing conditions of approximately 1.2 arcsec. The data processing was similar to that used for the HERON data. Throughout the observations, we carried out extensive dithering, with maximum separation of about 5 arcmin (half of the field of view) in order to obtain high efficiency in the low-surface-brightness regime, minimizing the presence of gradients and allowing us to build a flat field with the science images.

Due to the extensive dithering of the observations, the exposure time varies with position. In Fig. A.1 we show the exposure time and equivalent depth along the footprint of the observations. In the maximum exposure region of 10 h, the limiting surface brightness reaches 31.4 mag arcsec −2 [3 σ , 10″ × 10″] in the L luminance band. A relatively large portion of about 6 × 8 arcmin of the area of the image, including the central region of the stream, has a surface brightness limit of 31.0 mag arcsec −2 [3 σ , 10″ × 10″]. The resolution is 1.2 arcsec in full width at half maximum (FWHM).

The WHT luminance band image confirms the existence of the narrow feature identified in the HERON data, achieving deeper surface brightness limits and higher resolution (see Figs. 1 b and c) over the central region (14 × 17 arcmin) of the stream. We searched visually for potential remnants or overdensity from a parent galaxy. However, the stream appears completely featureless, especially in the higher resolution and deeper WHT image that samples the central region.

The detection of this stream in three images with two different telescopes allows us to confirm its discovery and to rule out a possible residual flux due to instrumentation or data processing.

The presence of globular clusters usually traces the trajectories of streams ( Mackey et al. 2019 ), and can also provide an estimate of their distance through measurement of the peak of the globular cluster luminosity function ( Rejkuba 2012 ). However, the HERON data do not have enough point-source depth, and do not allow color filtering with only the g and r bands. There are no HST data available over the area, and the only multi-band data available from DECaLS have insufficient point source depth, making detection of globular clusters infeasible until better data are obtained. In this section, we present an analysis performed to ensure that the detected feature is indeed a stellar stream located in Coma.

3.1. Potential resolved stars

We explore the possibility of the existence of an overdensity of point-like sources over the stream region, which would indicate a close distance. For this, we use SExtractor ( Bertin 2006 ) with a detection threshold of 1 σ . We do not apply any magnitude criteria other than selecting sources compatible with point-like sources, and for this we select sources with a stellarity index of higher than 0.5.

The middle panel of Fig. 2 shows the density of point-like sources that we can associate with low-luminosity stars. Interestingly, this stream is not resolved into stars in the WHT data, appearing as an extremely smooth and low-surface-brightness feature. Considering that this feature is not resolved into stars, we follow the analysis by Zackrisson et al. (2012) to impose a lower limit on distance. The fact that stars are unresolved in our highest-resolution data with a seeing of 1.2 arcsec and a surface brightness of approximately 29 mag arcsec −2 (detailed in later sections) suggests that the feature must be at a distance of at least 1 Mpc.

3.2. Far-infrared counterpart

In order to explore the possibility that the stream could be a trace of dust from the interstellar medium (ISM) or Galactic cirrus of the Milky Way, we used data available from the Herschel space telescope at 250 μm ( Pilbratt et al. 2010 ). Due to its low temperature, Galactic cirrus are efficiently detected in far-infrared (FIR) and submillimeter bands ( Low et al. 1984 ; Veneziani et al. 2010 ). The Herschel data at 250 μm offer a significant advantage over data from other instruments, such as IRAS ( Neugebauer et al. 1984 ) or the Planck observatory with its 857 GHz band ( Planck Collaboration XXIV 2011 ), both in detection power and – importantly for our case – resolution.

The lower panel of Fig. 2 shows a comparison between our optical data and the Herschel 250 μm band of the same field. The images have been stretched in the optical to provide maximum contrast for the detection of the faintest sources. The FWHM of the 250 μm Herschel data is 17.6 arcsec, which is lower than the detected stream width in optical bands of 1 arcmin. Visually, there is no emission trace in the 250 μm band, either in the region where the stream is located or adjacent to it. The only detectable emission in 250 μm is that corresponding to galaxies along the line of sight, among which we can highlight the strong emission from the late-type galaxy NGC 4848.

In order to quantify the 250 μm emission over the region of the stream, we calculated the total flux in the aperture defined by the dashed lines shown in Fig. 2 and outside this region. This aperture is defined using HERON optical data, and is detailed in Sect. 4.1 . This is done on the heavily masked image, avoiding the integration of regions corresponding to external sources that appear in the image. The average sky background value over the region of the stream is S ​ ν , 250 μm = −0.02 ± 0.04 MJy sr −1 and that outside this region is S ​ ν , 250 μm = 0.02 ± 0.01 MJy sr −1 . Therefore, the stream has no emission in the 250 μm band, at least up to the value defined by the sky background noise of these data.

The absence of a 250 μm counterpart to the optically detected stream suggests that the Galactic cirrus emission is an unlikely explanation for the origin of the feature. Additional reasons to rule out a Galactic cirrus contamination are that this celestial region is very close to the Galactic pole ( b = 88°), with a low extinction by dust ( A r = 0.02 mag; Schlafly & Finkbeiner 2011 ) and that the stream is almost one dimensional, not showing the expected fractal morphology of cirrus in optical wavelengths ( Marchuk et al. 2021 ).

3.3. Environmental analysis

The extremely low surface brightness of this feature makes it highly challenging to obtain spectroscopic information with which to measure its redshift. We have not found any gas detections in the region using the NASA/IPAC Extragalactic Database, nor counterparts in recent work by Bonafede et al. (2022) .

Assuming that the feature is indeed a stellar stream, its elongated morphology suggests that it must be a tidal feature and therefore should be associated with some structure that impacts it gravitationally. Considering its large apparent size, beyond the obvious possible association with the adjacent Coma cluster, we explored a potential association with some nearby structures in close projection.

Figure 3 shows a celestial coordinate map with large-scale structures in the line of sight of the stream. We make use of the catalogue of nearby groups within 3500 km s −1 by Kourkchi & Tully (2017) to identify these structures. Kourkchi & Tully (2017) also offer estimates of the virial radius of these structures.

We plot all groups together with their virial radii in Fig. 3 . We convert from physical to projected coordinates using the same cosmological parameters as those in Kourkchi & Tully (2017) with H 0 = 75 km s −1 Mpc −1 . Where a distance is not available for a group, we use a direct conversion by Hubble’s law using the radial velocity. We find that only sparse groups do not have measured distances, and in any case, they are not close in projection to the Coma Cluster. As a complement, and given that the Kourkchi & Tully (2017) catalogue only contains groups up to 3500 km s −1 , we plot galaxies with radial velocities of between 3500 and 10 000 km s −1 obtained from the NASA/IPAC Extragalactic Database as black points. This upper limit is used because it is the maximum radial velocity of the galaxies contained in the central region of the Coma cluster. To represent the virial radius of the Coma cluster, we rely on Ho et al. (2022) , giving 2.4 Mpc with H 0 = 75 km s −1 Mpc −1 . We also plot the length and location of the stream as a red segment.

We can comment on some nearby structures. First, the Virgo Galaxy Cluster, which could be a potential host for the stream, is located at approximately 13° projected separation from Coma. With a calculated virial radius of 1.3 Mpc for the Virgo Cluster, this corresponds to an apparent size of 4.4°. The stream would therefore be located at a projected distance of 3.9 times the virial radius of the Virgo Cluster. The M 94 group is the other structure with a large apparent size, having a virial radius of 365 kpc, which is equivalent to 4.4°. The stream is located at three times the virial radius of the M 94 Group. NGC 4725, located at a distance of 12 Mpc, has a virial radius of 143 kpc, equivalent to 0.63°, with the stream at 5.1 times its virial radius. Next, the group of NGC 4565, located at a distance of 13 Mpc, has a virial radius of 343 kpc, equivalent to 1.4°, leaving the stream at more than 4.4 times its virial radius. Finally, the closest structure in terms of virial radius is M 64, located at a distance of 5 Mpc, with a virial radius of 224 kpc, equivalent to 2.34°. The stream would therefore be projected at a distance of 2.8 times this virial radius.

We explored the possibility that the stream could be caused by a disturbance from a galaxy that overlaps with it in the line of sight. In Fig. 2 the most prominent candidates are identified by name. In particular, the pair of overlapping galaxies UGC 08071 and LEDA 083688 could be candidates to produce the stream. However, our very deep images do not show any sign of asymmetry in them. Furthermore, the radial velocities of UGC 08071 and LEDA 083688 are 6933 ± 2 km s −1 and 8169 ± 2 km s −1 , respectively, and these objects are therefore located more than 1200 km s −1 apart in velocity space (the radial velocity of galaxies in Coma ranges from 4000 to 10 000 km s −1 ). This makes it highly unlikely that they could have interacted at such a high velocity while leaving no asymmetry in the time during which the stream expanded. The other galaxies in the line of sight also show no appreciable asymmetry that would be compatible with the occurrence of the stream. We note that for a tidal-force calculation between galaxies in the line of sight, a distance value between them is necessary. However, in this case, a relative distance value is not easily obtained, considering that we are in a clustered environment, and that very close projections between galaxies might only be apparent. This would mean that galaxies in close projection could be separated by tens or even hundreds of kiloparsecs. We therefore consider the potential presence of disturbance in the outer parts of galaxy haloes to form the basis of the most reliable approach to identifying the presence of interaction between galaxies.

We further investigate a possible counterpart to a radio relic. Radio relics are diffuse structures detected in radio by synchrotron emission frequently found in interacting galaxy clusters (see a review by van Weeren et al. 2019 ). Notably, these radio relics are often found in the peripheral regions of galaxy clusters, with morphologies similar to those of the stream ( Feretti et al. 2012 ; Jee et al. 2015 ). Although no optical counterpart has been found for these radio relics by previous works, due to the extreme surface brightnesses that we explore in this work, it is interesting to look for a counterpart to a radio relic. However, we do not identify a counterpart in the deepest and most recent data in Coma by Bonafede et al. (2022) .

From this analysis, we conclude that the stream is embedded within the region of influence or virial radius of the Coma Galaxy Cluster, and does not overlap with the virial radius of any other structure in the line of sight. No other galactic association, such as a group or cluster, overlaps with the location of the stream, and there is no galaxy in the line of sight that could be the origin of the stream. This indicates that the stream is most likely associated with Coma and that there is no other particular galaxy or galactic association that can explain its clearly disturbed morphology.

4.1. Photometry

To better constrain the nature and possible origin of the stream, we performed a photometric analysis of the Giant Coma Stream with the two different datasets available to us. The HERON image provides two photometric bands g and r with surface brightness limits of 29.5 mag arcsec −2 [3 σ , 10″ × 10″] in g and r bands, respectively, in the region of interest, with a spatial resolution of ≈3 arcsec FWHM and completely covering the region. The WHT data partially cover the central region of the stream with an average depth of 31.0 mag arcsec −2 [3 σ , 10″ × 10″] in the luminance band and a spatial resolution of approximately 1.2 arcsec in FWHM. Given the different characteristics of the two datasets, we performed a different analysis on each, focusing on obtaining different photometric properties.

We first analyzed the photometry using the HERON data. In the top panel of Fig. 4 , we show a composite color image with both g and r bands from HERON. This image is useful for visualizing the full extent of the stream and its morphology. The apparent size in length and width of 18.5 × 1 arcmin by visual inspection corresponds to approximately 510 × 25 kpc at the Coma distance. The middle panels of Fig. 4 show the masking and subsequent binning (5 × 5 pixels, equivalent to 5.58 × 5.58 arcsec) of these data, allowing us to isolate the stream from external sources. We can see that the stream has a certain curvature. We estimate a radius of curvature of about 3620 arcsec, which is about 1°, and is equivalent to 1.7 Mpc. The Coma virial radius is 2.4 Mpc ( Ho et al. 2022 ). In the middle panel of Fig. 4 , we indicate with dashed lines the contours of an annular aperture of 45 arcsec in width with this calculated radius of curvature. This aperture is the width at which the stream is detected in the HERON data, corresponding approximately to a surface brightness of 30 mag arcsec −2 in the r band (the shallowest of the HERON data; see Sect. 2.1 ). This aperture is the same as the one used in Sect. 3.2 to explore the potential IR emission of the stream.

We use this aperture on the masked image to derive g and r band photometric profiles along the stream, which are shown in the lower panel of Fig. 4 . Because of the strong fluctuations in the profiles, we smooth them with a Gaussian kernel of approximately 10 binned pixel units in order to obtain a sufficient signal-to-noise ratio (S/N) in the profile. We calibrate the zero-flux sky level in the region adjacent to, but sufficiently far from, the stream. We find average surface brightnesses along the stream length of approximately 29.5 mag arcsec −2 in the g band and 29.0 mag arcsec −2 in the r band. The strong fluctuations of the photometric profiles of the stream are due to the extremely low surface brightness, together with the presence of masked regions, but also to possible systematic effects such as background fluctuation due to flat-fielding and sky subtraction.

Despite the obvious fluctuations, we observe that the difference between the g and r photometric profiles is relatively constant. Figure 5 shows the distribution of pixel color values for the stream. This latter faithfully follows a Gaussian function, compatible with a constant color that would correspond to the color of the stream. To obtain the average color and error, we calculate the mean value and error using a 3 σ robust mean, yielding g  −  r = 0.53 ± 0.05 mag. This color indirectly indicates that a potential lensing of a high-redshift background source amplified by Coma can be ruled out, as a high-redshift source should appear much redder in g  −  r color, and additionally, Coma is too nearby to act effectively as a lens. In complement to this, we fit the distribution with a Gaussian function that provides an equivalent value (see Fig. 5 ). In order to obtain a pseudo color g  −  L with which to relate the photometric magnitudes between HERON ( g and r bands) and WHT ( L band), we constructed an image with the average of the g and r bands. Using this pseudo L band, we carried out a similar analysis, which yielded g  −  L = 0.32 ± 0.03 mag.

We now focus on the analysis of the WHT data, with higher nominal depth and better resolution, albeit only available in the central region of the stream. Figure 6 shows a photometric profile along the cross-section of the stream. The left panel shows a high-contrast image binned 5 × 5 from the original pixel size of 0.2667 arcsec, giving at a pixel scale of 1.334 arcsec. The central panel, shows this same image with masking applied to hide external sources to the stream. This masking is performed with a combination of SExtractor , which aggressively hides mainly sources of small sizes ( DETECT_THRESH = 0.3), and a manual masking with wide circular apertures hiding larger galaxies and their expected haloes that could appear even below the surface brightness detectable visibly in the images. After this masking, the images are binned at 1.334 arcsec pix −1 , allowing the diffuse light to emerge efficiently (see Román et al. 2021 , for a similar processing).

Given the nearly straight morphology of the stream in this partial region, we project the combined flux in this direction, obtaining a photometric profile along the cross-section. This is done in the region of the image with a nominal depth of fainter than 31.0 mag arcsec −2 in the L band (see Fig. A.1 ), avoiding the outermost areas, which due to the dithering of the observations have a lower S/N. The whole region shown in the central panel is the one used for the photometric profile. For averaging, we use the median value along the stream direction, with errors calculated as 1 σ . We introduce a tilt plane that fits the sky background in order to eliminate a small gradient present in the profile. The obtained profile is smoothed with a three-pixel Gaussian kernel to eliminate small fluctuations from the effects of masking.

The maximum surface brightness of the stream is approximately 29.2 mag arcsec −2 in the L band. Using the previously calculated g  −  L color of 0.32 mag, this would translate into a maximum surface brightness of approximately 29.5 mag arcsec −2 in the g band, agreeing with the values obtained from the HERON data, and giving confidence to the results. The WHT profile reaches reliably down to a surface brightness of about 32 mag arcsec −2 , beyond which spurious fluctuations begin to show up, probably due to sky fluctuations and masking residuals. The shape of the profile is approximately straight in its slope, and is therefore compatible with an exponential decay. By analyzing this profile in flux units, we can identify an approximately Gaussian shape (see Fig. 7 ). By modeling this flux profile with a Gaussian function, the 1 σ fitted width has a value of 20.1 arcsec or 9.3 kpc. The FWHM is 42.3 arcsec or 19.5 kpc. We notice a small asymmetry in the profile, where on the left side (toward the direction where Coma is located) the profile shows a slight excess. However, this asymmetry is not strong, and is potentially caused by the masking residuals of nearby galaxies located in that region.

Due to the numerous sources overlapping the stream, a direct flux measurement is not possible. In order to obtain an integrated magnitude, we use the good fit to a Gaussian profile to model the total flux. To this end, we assume the average profile to be that obtained in the analysis of Fig. 7 in order to integrate it along the estimated length of 510 kpc (see Fig. 4 ). We consider this a relatively good approximation because of the approximately constant surface brightness along the entire length of the stream. The value produced is L = 20.90 ± 0.12 mag, which corresponds to g = 21.22 ± 0.15 mag according to the color g  −  L = 0.32 ± 0.03 mag calculated above. The absolute magnitude of the stream according to this model at the distance of Coma would therefore be L g = −13.78 ± 0.15 mag. Following mass to light ratio predictions by Roediger & Courteau (2015) , this translates to a stellar mass of M ⋆ = 6.8 ± 0.8 × 10 7   M ⊙ . We note the potential presence of uncertainties on the integrated photometric quantities, both because of systematic errors due to modeling and possible nondetection of further structure in our data. Therefore, integrated magnitudes are to be considered as order-of-magnitude estimates, and as lower limits on the mass of both the stream and its potential progenitor.

According to the predicted mass–metallicity relations for a galaxy of this range of stellar mass ( Panter et al. 2008 ; Simon 2019 ), a metallicity of approximately Z / H = −1 is expected. The color g  −  r = 0.53 ± 0.05 mag would therefore indicate that this is an old, passive dwarf galaxy according to single stellar population models by Vazdekis et al. (2015 ; see also Román & Trujillo 2017 ).

4.2. Similar structures in simulations

To obtain an idea of how such structures could arise in ΛCDM, we use the Illustris-TNG50 (TNG50 for short) simulations to insight the existence of similar streams in clusters. The TNG50 simulation has a box size ∼50 Mpc on a side and a baryonic mass-per-particle of ∼8.5 × 10 4   M ⊙ . TNG50 is part of the Illustris-TNG suite of galaxy simulations in different volumes, which all include gravity, magnetohydrodynamics, and a treatment for the most relevant physical processes involved in galaxy formation, such as star formation, metal enrichment, and stellar and black hole feedback ( Pillepich et al. 2018 ; Nelson et al. 2019 ).

It is difficult to estimate the frequency with which one should expect to observe the kind of thin structure seen for the Giant Coma Stream within the ΛCDM model. The formation of these thin structures will depend primarily on two circumstances: timing of the merger or infall, and the intrinsic properties of the progenitors. Tidal disruption that sets in too early with respect to the present time at z = 0 – at which we analyze the cluster – or progenitors that have overly extended intrinsic sizes will lead to stellar streams that are too wide to be comparable to the Giant Coma Stream. On the other hand, satellite infall that is too late or intrinsic sizes that are too compact will lead to insufficient disruption to generate stellar streams that are as long as this stream.

While the relatively small box size in TNG50 does not allow for clusters as massive as Coma to exist in the simulated volume, the high numerical resolution needed to resolve the inner properties of the progenitors with an estimated mass of M ⋆  ∼ 10 8 − 9   M ⊙ makes the 50 Mpc box the most adequate to conduct our analysis. From the TNG database, we use their friend-of-friends group information to identify spatially coherent groups ( Davis et al. 1985 ), the information about haloes and subhaloes as provided by Subfind catalogs ( Springel 2005 ; Dolag et al. 2009 ), and the SubLink merger trees ( Rodriguez-Gomez et al. 2015 ).

The most massive cluster in TNG50 (group 0) has a virial mass of M 200  ∼ 2 × 10 14   M ⊙ and a virial radius of r 200  ∼ 1200 kpc (virial quantities are defined at the radius where the average enclosed density is 200 times the critical density of the Universe). We note that the mass of Coma is approximately larger by a factor of ten, M 200  ∼ 2 × 10 15   M ⊙ ( Ho et al. 2022 ), which means that that even analyzing the highest-mass cluster in TNG50 falls short of an appropriate comparison. Nevertheless, our use of the TNG50 simulation is justified given the mass and spatial resolution needed to explore the presence of such narrow streams with dwarf-mass progenitors as those inferred in our calculations.

In order to identify similar stream structures, we selected all dwarf galaxies in the stellar mass range of M ⋆, max  = 10 8 − 9   M ⊙ that interacted with our group according to the SubLink merger trees; we refer to these as progenitors. The selection is done at the time of maximum stellar mass, M ⋆, max . This gives us a total of 342 progenitors for group 0. We then focused our search on progenitors that have lost a significant fraction of their maximum stellar content, f ⋆, bound  < 45%, where the bound fraction refers to the fraction of stellar mass at z  = 0 compared to the maximum stellar mass, because we are interested in progenitors of a sizable stellar stream. This cut is used as it is close to but smaller than half the maximum stellar mass of all satellites. In any case, the exact value of the cut has little impact on our results. For example, choosing all progenitors retaining 50% of their mass would only add two objects to the sample, which were identified to be accreted very late and to leave remnants at much larger distances than the observed structure. We therefore decided to keep our 45% mass cut as a good proxy for our progenitors.

In addition, to identify progenitors that created structures further out in the halo of the cluster, we require that the median radius ( r 50 ) of the stellar debris, here simply defined as the material that has been tidally removed according to our substructure finder Subfind, be larger than 800 kpc. Our final sample comprises 19 progenitors. The main panel in Fig. 8 shows an image created from the stellar debris of this sample.

Encouragingly, within this sample, we find one particular stream with characteristics that are reminiscent of those of the Giant Coma Stream. The analogous structure is highlighted in cyan in the main panel of Fig. 8 and then shown in three perpendicular projections in the smaller panels on the right. Not only is this stream narrow and very extended as in the case of the Giant Coma Stream, but also under the right projection it appears as an almost straight line (when the projection is close to the orbital plane). We note that the center of curvature of the stream points toward the center of the cluster, as is the case for the Giant Coma Stream. This could be considered as further evidence that indeed the Giant Coma Stream belongs to Coma, because the approximate center of curvature coincides with the center of the gravitational potential about which they orbit ( Nibauer et al. 2023 ).

Our simulated analog has a progenitor stellar mass of M ⋆, max  = 1.1 × 10 8 and has lost ∼75% of its original mass at the present day, which is defined at snapshot 98 in the simulation, or redshift z  = 0.009. Interestingly, the formation history of this stream is somewhat noncanonical, as the gravitational potential of the clusters is not the only environment responsible for the stellar stream formation. The tidal disruption leading to the formation of this thin stream seems to start as part of preprocessing in a smaller group environment. Our analog is first accreted into another group with a virial mass of M 200  = 5.48 × 10 11   M ⊙ at infall time t inf  = 2.98 Gyr ( z inf  = 2.2, defined as the last time this dwarf galaxy was centered in its own dark matter halo). Only at later times, by t  = 6.5 Gyr, does the analog join the friends-of-friends group of the main cluster, only crossing its virial radius by t  ∼ 12.7 Gyr, making it a relatively recent accretion. At the final time, the analog has gone through only one pericenter around the main cluster, from which it recently emerged and is on its way to the first apocenter. The center of the group where the preprocessing occurred is currently more than 1000 kpc away from our analog.

The numerical resolution of TNG50 is insufficient to study the morphology of the stream in detail, for example, in terms of width or the light profile across the stream, for which hundreds of thousands of stellar particles would be needed to faithfully trace the structure (compared to the ∼10 000 available in TNG50 for this progenitor). Instead, this simulation provides a idea of a possible formation scenario for very narrow and long stellar streams in massive galaxy clusters, demonstrating that they do occur within the current cosmological scenario. Tailored idealized simulations would be the obvious next step to study and understand the detailed properties of the stream in terms of width, light profile, and color gradients.

The properties of the Giant Coma Stream are remarkable. Its thin and coherent morphology is reminiscent of cold stellar streams observed in the Milky Way (e.g., Odenkirchen et al. 2003 ; Grillmair & Dionatos 2006 ; Balbinot et al. 2016 ) or streams in the Andromeda Galaxy (see a review by Ferguson & Mackey 2016 ). Its surface brightness peaks at a very faint level of 29.5 mag arcsec −2 in the g band (see Fig. 6 ), which is comparable to the surface brightness of the Giant Stream in the Andromeda Galaxy ( Ibata et al. 2001 ). However, the size of the Giant Coma Stream, with a detected length of approximately 510 kpc, is longer than any known “giant” stream in the literature ( Ibata et al. 2001 ; Martínez-Delgado et al. 2009 , 2021 , 2023b ). To the best of our knowledge, no stellar stream of such size has ever been detected, nor has a stream of such low surface brightness been seen in surface photometry observations.

Previous work in Coma and other galaxy clusters revealed the presence of tidally disrupted objects ( Trentham & Mobasher 1998 ; Gregg & West 1998 ; Conselice & Gallagher 1999 ; Calcáneo-Roldán et al. 2000 ) showing evidence for the build up of the intracluster light by accretion of substructures. We now discuss some particular cases. First, the plume-like object discovered by Gregg & West (1998) in the heart of Coma is 130 kpc long and about 15−30 kpc wide. Its surface brightness is much brighter ( μ R  = 25.7 mag arcsec −2 ) than that of the Giant Coma Stream, as is its integrated luminosity ( R  = 15.6 ± 0.1 mag), and it is of a much redder color, namely g  −  r  ≈ 0.75 mag ( Gregg & West 1998 ). A simple calculation shows that the stellar mass of this plume-like object is approximately 10 10 solar masses, indicating that the remnant is a much more massive galaxy than a dwarf, and is probably an elliptical galaxy, discarding a common origin. While the properties and locations of this plume-like object and the Giant Coma Stream differ, it is interesting that both share the same orientation, and that this orientation coincides in their alignment with the main filament that feeds Coma (see Malavasi et al. 2020 ). Additionally, correlated accretion due to the orientation of filaments and large-scale structure is expected to occur within ΛCDM (e.g., Libeskind et al. 2014 ). Another interesting object is the arc located in the Centaurus cluster discovered by Calcáneo-Roldán et al. (2000) . Its morphology is remarkably similar to that of the Giant Coma Stream, with a linear and featureless appearance, and a length of ∼170 kpc ( Calcáneo-Roldán et al. 2000 ). However, the surface brightness is considerably higher than that of the Giant Coma Stream with μ R  = 26.1 mag arcsec −2 . Calcáneo-Roldán et al. (2000) argue that this object could be a tidally disrupted luminous spiral galaxy.

Several more recent studies have been carried out in a number of galaxy clusters ( Giallongo et al. 2014 ; Montes & Trujillo 2018 , 2022 ; DeMaio et al. 2018 ; Montes et al. 2021 ; Jiménez-Teja et al. 2021). The surface brightness and resolution (due to the close proximity of the Coma cluster) achieved in our work are unprecedented, with one exception. The Burrell Schmidt Deep Virgo Survey ( Mihos et al. 2017 ) is comparable in terms of depth to our observations with the addition of a better resolution due to the proximity of the Virgo Cluster. Indeed, a large number of thin stellar streams appear in the central region of Virgo; for example, a pair of streams to the NW of M87 with lengths of around 150 kpc and similarly thin morphologies and widths of on the order of tens of kiloparsecs (streams A and B by Mihos et al. 2005 ; Rudick et al. 2010 ), as well as a myriad of much smaller streams or tidal features associated with different galaxies in the field of Virgo ( Mihos et al. 2017 ).

A fundamental characteristic that differentiates the Giant Coma Stream from the streams detected in Virgo is that it is not associated with any particular galaxy but is a free-floating structure in the external regions of Coma. Dynamically cold and extremely faint stellar streams are thought to form through strong tidal fields in low-mass accretion events ( Bullock & Johnston 2005 ), and in the case of galaxy clusters through interactions of low-mass galaxies passing through the inner region of the clusters ( Romanowsky et al. 2012 ; Cooper et al. 2015 ). These streams are fragile, and dynamical times of one or two times the crossing time are enough to destroy them ( Rudick et al. 2009 ). It is therefore striking that the Giant Coma Stream is a free-floating stream far from the center of the cluster, with such a coherent and fragile morphology.

We argue that the lack of detected free-floating streams in Virgo could be due to two factors. First, Coma is much more massive than Virgo, which implies a much higher velocity dispersion, σ v = 1008 km s −1 for Coma ( Struble & Rood 1999 ) versus σ v = 638 km s −1 for Virgo ( Kashibadze et al. 2020 ), and so high-velocity galaxies are more common in Coma. Second, a free-floating stream in Virgo would be expected to lie in the periphery of the cluster, but due to the proximity of Virgo, the deep data provided by Mihos et al. (2017) are limited to its central region. If a similar feature exists at a projected distance of the Giant Coma Stream, namely 0.8 Mpc, in Virgo, that stream would be outside the footprint of these observations and therefore undetected. This makes it potentially interesting to explore the outermost regions of the Virgo cluster or other nearby clusters in a search for similar free-floating streams analogous to the Giant Coma Stream.

The presence of an analog stream in the TNG-50 simulation may indicate that such free-floating streams with cold or thin morphology may be common in galaxy clusters. There is no guarantee that the Giant Coma Stream was formed by a complex interaction like the one depicted by our analog. However, it is encouraging that we find at least one analog in the formation history of a galaxy cluster. Our analysis indicates that while typical debris from this type of progenitor tends to be wider and less coherent than the Giant Coma Stream, at least there is one case where the narrowness and length of the stellar stream are comparable to it, suggesting that such structures may occur in ΛCDM. The recent accretion of this analog is compatible with the fragility of this type of structure, which, as mentioned above, is typically able to survive only one or two times the crossing time in its orbit by the cluster, making it very likely that the Giant Coma Stream is a recent accretion.

The potential presence of such thin stellar streams of cold morphology in galaxy clusters could extend the environmental range of their study from galactic to cluster scales. If cold stellar streams of considerably larger sizes than those found in the Local Group were found to be common, this would make current projections of their detectability much more optimistic ( Pearson et al. 2019 ), and future observational work, including by Euclid , the Rubin Observatory, the Nancy Grace Roman Space Telescope or ARRAKIHS, will be necessary in order to unveil similar structures in galaxy clusters and the properties of both the Giant Coma Stream and potential new discoveries.

One of the imminent and most impactfull applications of the study of cold stellar streams is related to the possibility of testing the shapes of the dark matter haloes and the subhalo distribution in their hosts, as the presence and number of subhaloes is ultimately defined by the properties of dark matter particles ( Ibata et al. 2002 ; Carlberg 2012 ; Erkal & Belokurov 2015 ). Ongoing work includes the analysis of the morphology and kinematics of cold stellar streams in the Milky Way, with the objective of tracing the global gravitational potential and also analyzing the possible impact of a low-mass dark matter subhalo that could perturb these streams both morphologically and kinematically ( Erkal et al. 2016 ; Banik & Bovy 2019 ; Ibata et al. 2020 ; Banik et al. 2021 ).

The available observational data for the Giant Coma Stream are insufficient in both resolution and depth and therefore do not allow a detailed analysis of this stream. We recall that the maximum resolution of our data is approximately 1.2 arcsec FWHM, which is equivalent to 550 pc at the Coma distance. Additionally, radial velocity measurements of individual stars are fundamental to these analyses ( Pearson et al. 2022 ). While current instrumental capabilities do not allow for such analyses, the new generation of extremely large-aperture telescopes may have sufficient observational capabilities for these studies.

In this work, we report the discovery of the Giant Coma Stream, a stellar stream with an extremely coherent and thin morphology, located at a distance of 0.8 Mpc from the center of the Coma cluster, and reminiscent of the cold stellar streams detected in the Milky Way.

The properties of the Giant Coma Stream are striking: a maximum surface brightness of μ g = 29.5 mag arcsec −2 and a length of 510 kpc. This makes it the faintest stream ever detected by surface photometry. The stellar mass is estimated to be M ⋆ = 6.8 ± 0.8 × 10 7   M ⊙ with a color of g  −  r = 0.53 ± 0.05 mag, which is consistent with a passive dwarf galaxy being the potential progenitor for the Giant Coma Stream. We do not identify any potential galaxy remnant or core, and the stream structure appears featureless in our data.

The Giant Coma Stream is orders of magnitude fainter in surface brightness than previous tidal features discovered in Coma and other clusters ( Trentham & Mobasher 1998 ; Gregg & West 1998 ; Conselice & Gallagher 1999 ; Calcáneo-Roldán et al. 2000 ). It is comparable in surface brightness to the thin streams detected in Virgo ( Mihos et al. 2017 ), however unlike these, the Giant Coma Stream does not appear to be associated with any particular galaxy, appearing as a free-floating feature in the outer regions of Coma.

Through analysis of the Illustris-TNG50 simulation, we find a remarkably similar analog, suggesting that such giant, extremely faint, and free-floating thin stellar streams may exist in galaxy clusters according to Λ-CDM.

This work shows a glimpse of the kind of structures waiting to be discovered in the ultralow-surface-brightness Universe. These structures, such as the Giant Coma Stream, show promising properties in revealing the ongoing hierarchical assembly of galaxy clusters and potentially unveiling the ultimate nature of dark matter.

We thank the two anonymous referees for a thorough review of our work. We thank Chris Mihos, Garreth William Martin and Claudio Dalla Vecchia for interesting discussions about the result. We acknowledge financial support from the State Research Agency (AEI-MCINN) of the Spanish Ministry of Science and Innovation under the grant “The structure and evolution of galaxies and their central regions” with reference PID2019-105602GB-I00/10.13039/501100011033, from the ACIISI, Consejería de Economía, Conocimiento y Empleo del Gobierno de Canarias and the European Regional Development Fund (ERDF) under grant with reference PROID2021010044, and from IAC project P/300724, financed by the Ministry of Science and Innovation, through the State Budget and by the Canary Islands Department of Economy, Knowledge and Employment, through the Regional Budget of the Autonomous Community. J.R. acknowledges funding from University of La Laguna through the Margarita Salas Program from the Spanish Ministry of Universities ref. UNI/551/2021-May 26, and under the EU Next Generation. R.M.R. acknowledges financial support from his late father Jay Baum Rich. I.T. and G.G. acknowledge support from the ACIISI, Consejería de Economía, Conocimiento y Empleo del Gobierno de Canarias and the European Regional Development Fund (ERDF) under grant with reference PROID2021010044 and from the State Research Agency (AEI-MCINN) of the Spanish Ministry of Science and Innovation under the grant PID2019-107427GB-C32 and IAC project P/302300, financed by the Ministry of Science and Innovation, through the State Budget and by the Canary Islands Department of Economy, Knowledge and Employment, through the Regional Budget of the Autonomous Community. The operation of the Jeanne Rich Telescope was assisted by David Gedalia and Osmin Caceres and is hosted by the Polaris Observatory Association. This work is based on service observations made with the William Herschel Telescope (programme SW2021a15) operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

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Appendix A: Exposure times and depth in the WHT data

The left panel of Fig. A.1 shows the exposure time footprint for the WHT data. In order to provide a map of surface brightness limits, we performed the correlation between the standard deviation for pixels with equal exposure time and the exposure time. This correlation is shown graphically in Fig. A.2 . The parameters of the best fit are

measured as 3 σ in 10×10 arcsec boxes. By means of this obtained relation, we can make a surface brightness map using the exposure time values for each pixel. This map is shown in the right panel of Fig. A.1 .

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The long struggle to free Evan Gershkovich from a Moscow prison

By Lesley Stahl

Updated on: March 24, 2024 / 11:02 AM EDT / CBS News

On March 29, 2023, Evan Gershkovich was on assignment in Russia when he was arrested by security forces and accused of being a spy , a charge vigorously denied by Gershkovich, the Wall Street Journal, and the U.S. government.

Look around the Wall Street Journal offices in Manhattan, and you'll see Gershkovich, the hostage, everywhere – on buttons, cards, shirts, and screens that stop you in your tracks.

Emma Tucker, the Journal's editor-in-chief, said that – unlike the Iran hostage situation, when the U.S. government told families to avoid publicity and let the government quietly negotiate – her instinct was to draw attention to Gershkovich's detainment. "Because it was so clearly outrageous," she said. "He was accredited. He was doing his job. He had done nothing wrong. My sense of justice was offended by what had happened."

Gershkovich was the first reporter to be taken into custody like this since the Cold War.

When asked why him, Tucker replied, "It's very hard to know. Is it because he works for the Wall Street Journal, which is a recognizable, famous American title? Is it because he's of Russian heritage? I wish I knew."

What is known is that Gershkovich is being held in a Stalin-era prison in Moscow. His pre-trial detention has been extended several times. Court appearances have been few but jarring.

"It was horrible," Tucker said, of seeing Gershkovich in court. "There's something so dehumanizing about those glass cages. I was surprised at the shock I felt at seeing it. So, goodness only knows what his parents felt when they saw it. So yes, it was a shock. At the same time, he was standing tall. He looked defiant. He smiled. So, mixed emotions."

In her apartment, where her younger brother would crash on the couch, Danielle Gershkovich said his calling was never in question. "I think he was born to be a journalist," she said. "He, I think, had always been seeking a life of adventure. And his travel, his writing. Working at the Wall Street Journal as a Russia correspondent was his absolute dream job."

Children of Soviet emigres who spoke Russian at home, Danielle and Evan have always been close. Hearing that he was in custody was shattering.

"I got a call from my mom," she said. "And it's just, my stomach fell out, you know? Your heart stops. It's so hard to believe that something like that is actually real. And I remember my mom and I discussing the morning after: 'Is that really Evan, that photo that came out?' We didn't want to admit for a moment that that was him."

Stahl asked, "Did you think [detention] was a possibility? Russia a year ago had already become dangerous. Other news organizations were pulling reporters out."

"I would say my whole family was nervous," Danielle replied. "He would always remind us, he's an accredited journalist."

And, therefore, (supposedly) safe. "It's very unprecedented," Danielle said.

Of course, what was unprecedented has become almost routine under Russian President Vladimir Putin. Gershkovich is the latest American pawn on Putin's geopolitical chessboard against the West.

Marine veteran Paul Whelan has been jailed in Russia for five years; Russian-American ballerina Ksenia Karelina was arrested in January, accused of treason for helping Ukraine; and basketball star Brittney Griner , imprisoned for nine months on drug charges, was finally freed in an exchange for a notorious arms dealer known as the "Merchant of Death."

Former world chess champion Garry Kasparov, who fled Russia in 2013, is one of Putin's most fervent critics. When asked if he fears for his life, he replied, "Would it help?"

Kasparov was recently named by the Kremlin to its registry of people it considers to be terrorists and extremists . He calls it "a badge of honor."  

Stahl asked, "Putin just gets stronger and stronger, it seems, rather than the other way, which you predicted once that he would be on the downswing?"

"Putin's strength is very much result of [the West's] weakness," Kasparov replied. "Any sign of indecisiveness, any sign of hesitation feeds Putin with power. Because [he'll say], 'Ha, ha, yes, I can do this, I can do that. Nothing will happen.'"

He believes there is no chance that Gershkovich would be acquitted of charges. "Putin treats Gershkovich as money or weapons," he said. "This is one of the tools of him staying in power. So, he'll be negotiating."

WEB EXTRA:  Garry Kasparov on how Western indecisiveness emboldens Putin (YouTube Video)

Putin himself has made that clear. He said he was open to a prisoner swap involving Gershkovich, Whelan, and a deal for opposition leader Alexey Navalny right before he died in a Russian prison last month .

•  Arrest of Wall Street Journal reporter in Russia likely "approved at the highest levels," ex-U.S. ambassador says
• Wall Street Journal reporter Evan Gershkovich's latest appeal denied by Russia court
• Russian court extends Wall Street Journal reporter Evan Gershkovich's detention by 3 months

Roger Carstens, the U.S. Special Envoy for Hostage Affairs, said, "What I can tell you is that the United States has been negotiating with the Russians." He did not deny that a swap was in the works, and it fell apart when Navalny died. "We had a strong offer that went at the end of last year," Carstens said. "The Russians rejected it. I was rather disappointed, but it might not have been entirely a huge surprise. But our goal now is to keep working with partners, allies, and to find that combination that's going to allow us to solve it."

Stahl asked, "How many Americans are being held hostage in the world?"

"My numbers at one point were over 50," said Carstens. "They're now down in-between 20 and 30. We always hesitate to give out an exact number for various reasons. In the last three years, the Biden-Harris administration has brought back 46 Americans that were wrongfully detained or held hostage. It's a team effort; it's members of U.S. government, members on Capitol Hill, non-profits, NGOs, allies, partners, and even members of the media that all seem to work together to bring those people home."

Carstens reiterated that Evan Gershkovich has never worked for the U.S. government. "He's not a spy; he's a journalist," he said. "And journalism should not be a crime."

Gershkovich spends 23 hours a day in his cell. Wall Street Journal editor-in-chief Emma Tucker says he's allowed to send and receive letters, as long as they're in Russian. She described Gershkovich as "a resilient character. He's an extrovert, he's a people person."

And his health? "I think his health is okay; his mom looks very closely whenever there are shots of him [on TV]," Tucker said. "I think there's limits to how much exercise he can do. I can only imagine what the food is like. But he's meditating. He's practicing and getting ever better at Russian. He's reading in Russian."

And he even managed, from prison, to deliver something very special to his sister, Danielle: Flowers, which arrived for International Women's Day on March 8. "He's always thinking about us, and finding ways to make us smile," Danielle said.

Stahl said, "From the minute I walked in here, your eyes keep watering. It's hard for you to talk about, or not? Maybe it helps you?"

"Maybe it's that bittersweet moment where I'm looking at his photos," Danielle said. "I wish I didn't have to do this, but talking about my brother is always … it makes me smile. I miss him so much."

      For more info:

• Evan Gershkovich, The Wall Street Journal

       Story produced by Gabriel Falcon. Editor: Ed Givnish. 

      See also: 

• Husband of U.S. journalist Alsu Kurmasheva detained in Russia: "I'm not going to give up" ("Sunday Morning")
• Evan Gershkovich
• Vladimir Putin

One of America's most recognized and experienced broadcast journalists, Lesley Stahl has been a "60 Minutes" correspondent since 1991.

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