the primary sources of literature review are the following except

Literature review sources

Sources for literature review can be divided into three categories as illustrated in table below. In your dissertation you will need to use all three categories of literature review sources:

Sources for literature review and examples

Generally, your literature review should integrate a wide range of sources such as:

• Books . Textbooks remain as the most important source to find models and theories related to the research area. Research the most respected authorities in your selected research area and find the latest editions of books authored by them. For example, in the area of marketing the most notable authors include Philip Kotler, Seth Godin, Malcolm Gladwell, Emanuel Rosen and others.
• Magazines . Industry-specific magazines are usually rich in scholarly articles and they can be effective source to learn about the latest trends and developments in the research area. Reading industry magazines can be the most enjoyable part of the literature review, assuming that your selected research area represents an area of your personal and professional interests, which should be the case anyways.
• Newspapers can be referred to as the main source of up-to-date news about the latest events related to the research area. However, the proportion of the use of newspapers in literature review is recommended to be less compared to alternative sources of secondary data such as books and magazines. This is due to the fact that newspaper articles mainly lack depth of analyses and discussions.
• Online articles . You can find online versions of all of the above sources. However, note that the levels of reliability of online articles can be highly compromised depending on the source due to the high levels of ease with which articles can be published online. Opinions offered in a wide range of online discussion blogs cannot be usually used in literature review. Similarly, dissertation assessors are not keen to appreciate references to a wide range of blogs, unless articles in these blogs are authored by respected authorities in the research area.

Your secondary data sources may comprise certain amount of grey literature as well. The term grey literature refers to type of literature produced by government, academics, business and industry in print and electronic formats, which is not controlled by commercial publishers. It is called ‘grey’ because the status of the information in grey literature is not certain. In other words, any publication that has not been peer reviewed for publication is grey literature.

The necessity to use grey literature arises when there is no enough peer reviewed publications are available for the subject of your study.

John Dudovskiy

• Library Guides

The Literature Review

Primary and secondary sources, the literature review: primary and secondary sources.

• Searching the literature
• Grey literature
• Organising and analysing
• Systematic Reviews
• The Literature Review Toolbox

On this page

• Primary vs secondary sources: The differences explained 

Can something be both a primary and secondary source?

Research for your literature review can be categorised as either primary or secondary in nature. The simplest definition of primary sources is either original information (such as survey data) or a first person account of an event (such as an interview transcript). Whereas secondary sources are any publshed or unpublished works that describe, summarise, analyse, evaluate, interpret or review primary source materials. Secondary sources can incorporate primary sources to support their arguments.

Ideally, good research should use a combination of both primary and secondary sources. For example, if a researcher were to investigate the introduction of a law and the impacts it had on a community, he/she might look at the transcripts of the parliamentary debates as well as the parliamentary commentary and news reporting surrounding the laws at the time. 

Examples of primary and secondary sources

Primary vs secondary sources: The differences explained

Finding primary sources

• VU Special Collections  - The Special Collections at Victoria University Library are a valuable research resource. The Collections have strong threads of radical literature, particularly Australian Communist literature, much of which is rare or unique. Women and urban planning also feature across the Collections. There are collections that give you a picture of the people who donated them like Ray Verrills, John McLaren, Sir Zelman Cowen, and Ruth & Maurie Crow. Other collections focus on Australia's neighbours – PNG and Timor-Leste.
• POLICY - Sharing the latest in policy knowledge and evidence, this database supports enhanced learning, collaboration and contribution.
• Indigenous Australia  -  The Indigenous Australia database represents the collections of the Aboriginal and Torres Strait Islander Commission Library.
• Australian Heritage Bibliography - Aboriginal and Torres Strait Islander Subset (AHB-ATSIS)  - AHB is a bibliographic database that indexes and abstracts articles from published and unpublished material on Australia's natural and cultural environment. The AHB-ATSIS subset contains records that specifically relate to the Aboriginal and Torres Strait Islander peoples.include journal articles, unpublished reports, books, videos and conference proceedings from many different sources around Australia. Emphasis is placed on reports written or commissioned by government and non-government heritage agencies throughout the country.
• ATSIhealth  - The Aboriginal and Torres Strait Islander Health Bibliography (ATSIhealth), compiled by Neil Thomson and Natalie Weissofner at the School of Indigenous Australian Studies, Kurongkurl Katitjin, Edith Cowan University, is a bibliographic database that indexes published and unpublished material on Australian Indigenous health. Source documents include theses, unpublished articles, government reports, conference papers, abstracts, book chapters, books, discussion and working papers, and statistical documents. 
• National Archive of Australia  - The National Archives of Australia holds the memory of our nation and keeps vital Australian Government records safe. 
• National Library of Australia: Manuscripts  - Manuscripts collection that is wide ranging and provides rich evidence of the lives and activities of Australians who have shaped our society.
• National Library of Australia: Printed ephemera  - The National Library has been selectively collecting Australian printed ephemera since the early 1960s as a record of Australian life and social customs, popular culture, national events, and issues of national concern.
• National Library of Australia: Oral history and folklore - The Library’s Oral History and Folklore Collection dates back to the 1950’s and includes a rich and diverse collection of interviews and recordings with Australians from all walks of life.
• Historic Hansard - Commonwealth of Australia parliamentary debates presented in an easy-to-read format for historians and other lovers of political speech.
• The Old Bailey Online - A fully searchable edition of the largest body of texts detailing the lives of non-elite people ever published, containing 197,745 criminal trials held at London's central criminal court.

Whether or not a source can be considered both primary and  secondary, depends on the context. In some instances, material may act as a secondary source for one research area, and as a primary source for another. For example, Niccolò Machiavelli’s The Prince , published in 1513, is an important secondary source for any study of the various Renaissance princes in the Medici family; but the same book is also a primary source for the political thought that was characteristic of the sixteenth century because it reflects the attitudes of a person living in the 1500s.

Source: Craver, 1999, as cited in University of South Australia Library. (2021, Oct 6).  Can something be a primary and secondary source?.  University of South Australia Library. https://guides.library.unisa.edu.au/historycultural/sourcetypes

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• UConn Library
• Literature Review: The What, Why and How-to Guide
• Strategies to Find Sources

Literature Review: The What, Why and How-to Guide — Strategies to Find Sources

• Getting Started
• Introduction
• How to Pick a Topic
• Evaluating Sources & Lit. Reviews
• Tips for Writing Literature Reviews
• Writing Literature Review: Useful Sites
• Citation Resources
• Other Academic Writings

The Research Process

Planning : Before searching for articles or books, brainstorm to develop keywords that better describe your research question.

Searching : While searching, take note of what other keywords are used to describe your topic, and use them to conduct additional searches

     ♠ Most articles include a keyword section

     ♠ Key concepts may change names throughout time so make sure to check for variations

Organizing : Start organizing your results by categories/key concepts or any organizing principle that make sense for you . This will help you later when you are ready to analyze your findings

Analyzing : While reading, start making notes of key concepts and commonalities and disagreement among the research articles you find.

♠ Create a spreadsheet  to record what articles you are finding useful and why.

♠ Create fields to write summaries of articles or quotes for future citing and paraphrasing .

Writing : Synthesize your findings. Use your own voice to explain to your readers what you learned about the literature on your topic. What are its weaknesses and strengths? What is missing or ignored?

Repeat : At any given time of the process, you can go back to a previous step as necessary.

Advanced Searching

All databases have Help pages that explain the best way to search their product. When doing literature reviews, you will want to take advantage of these features since they can facilitate not only finding the articles that you really need but also controlling the number of results and how relevant they are for your search. The most common features available in the advanced search option of databases and library online catalogs are:

• Boolean Searching (AND, OR, NOT): Allows you to connect search terms in a way that can either limit or expand your search results 
• Proximity Searching (N/# or W/#): Allows you to search for two or more words that occur within a specified number of words (or fewer) of each other in the database
• Limiters/Filters : These are options that let you control what type of document you want to search: article type, date, language, publication, etc.
• Question mark (?) or a pound sign (#) for wildcard: Used for retrieving alternate spellings of a word: colo?r will retrieve both the American spelling "color" as well as the British spelling "colour." 
• Asterisk (*) for truncation: Used for retrieving multiple forms of a word: comput* retrieves computer, computers, computing, etc.

Want to keep track of updates to your searches? Create an account in the database to receive an alert when a new article is published that meets your search parameters!

• EBSCOhost Advanced Search Tutorial Tips for searching a platform that hosts many library databases
• Library's General Search Tips Check the Search tips to better used our library catalog and articles search system
• ProQuest Database Search Tips Tips for searching another platform that hosts library databases

There is no magic number regarding how many sources you are going to need for your literature review; it all depends on the topic and what type of the literature review you are doing:

► Are you working on an emerging topic? You are not likely to find many sources, which is good because you are trying to prove that this is a topic that needs more research. But, it is not enough to say that you found few or no articles on your topic in your field. You need to look broadly to other disciplines (also known as triangulation ) to see if your research topic has been studied from other perspectives as a way to validate the uniqueness of your research question.

► Are you working on something that has been studied extensively? Then you are going to find many sources and you will want to limit how far back you want to look. Use limiters to eliminate research that may be dated and opt to search for resources published within the last 5-10 years.

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Literature Review: Lit Review Sources

• Lit Review Types
• GRADE System
• Do a Lit Review
• Citation Justice
• Lit Review Sources
• AI for Research This link opens in a new window

Where do I find information for a literature review?

Research is done by...

...by way of...

...communicated through...

...and organized in...

Types of sources for a review...

• Primary source: Usually a report by the original researchers of a study (unfiltered sources)
• Secondary source: Description or summary by somebody other than the original researcher, e.g. a review article (filtered sources)
• Conceptual/theoretical: Papers concerned with description or analysis of theories or concepts associated with the topic
• Anecdotal/opinion/clinical: Views or opinions about the subject that are not research, review or theoretical (case studies or reports from clinical settings)

A Heirarchy of research information:

Source: SUNY Downstate Medical Center. Medical Research Library of Brooklyn. Evidence Based Medicine Course. A Guide to Research Methods: The Evidence Pyramid: http://library.downstate.edu/EBM2/2100.htm

Life Cycle of Publication

Click image to enlarge

Scientific information has a ‘life cycle’ of its own… it is born as an idea, and then matures and becomes more available to the public. First it appears within the so-called ‘invisible college’ of experts in the field, discussed at conferences and symposia or posted as pre-prints for comments and corrections. Then it appears in the published literature (the primary literature), often as a journal article in a peer-reviewed journal.

Researchers can use the indexing and alerting services of the secondary literature to find out what has been published in a field. Depending on how much information is added by the indexer or abstracter, this may take a few months (though electronic publication has sped up this process). Finally, the information may appear in more popular or reference sources, sometimes called the tertiary literature.

The person beginning a literature search may take this process in reverse: using tertiary sources for general background, then going to the secondary literature to survey what has been published, following up by finding the original (primary) sources, and generating their own research Idea.

(Original content by Wade Lee-Smith)

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Chapter 2: What is a Literature Review?

Learning objectives.

At the conclusion of this chapter, you will be able to:

• Recognize how information is created and how it evolves over time.
• Identify how the information cycle impacts the reliability of the information.
• Select information sources appropriate to information need.

2.1 Overview of information

Because a literature review is a summary and analysis of the relevant publications on a topic, we first have to understand what is meant by ‘the literature’.  In this case, ‘the literature’ is a collection of all of the relevant written sources on a topic.  It will include both theoretical and empirical works.  Both types provide scope and depth to a literature review.

2.1.1 Disciplines of knowledge

When drawing boundaries around an idea, topic, or subject area, it helps to think about how and where the information for the field is produced. For this, you need to identify the disciplines of knowledge production in a subject area.

Information does not exist in the environment like some kind of raw material. It is produced by individuals working within a particular field of knowledge who use specific methods for generating new information. Disciplines are knowledge-producing and -disseminating systems which consume, produce and disseminate knowledge. Looking through a  course catalog of a post-secondary educational institution gives clues to the structure of a discipline structure. Fields such as political science, biology, history and mathematics are unique disciplines, as are education and nursing, with their own logic for how and where new knowledge is introduced and made accessible.

You will need to become comfortable with identifying the disciplines that might contribute information to any search strategy. When you do this, you will also learn how to decode the way how people talk about a topic within a discipline. This will be useful to you when you begin a  review of the literature in your area of study.

For example, think about the disciplines that might contribute information to a the topic such as  the role of sports in society. Try to anticipate the type of perspective each discipline might have on the topic. Consider the following types of questions as you examine what different disciplines might contribute:

• What is important about the topic to the people in that discipline?
• What is most likely to be the focus of their study about the topic?
• What perspective would they be likely to have on the topic?

In this example, we identify two disciplines that have something to say about the role of sports in society: allied health and education. What would each of these disciplines raise as key questions or issues related to that topic?

2.1.1.1 Nursing

• how sports affect individuals’ health and well-being
• assessing and treating sports injuries
• physical conditioning for athletes

2.1.1.2 Education

• how schools privilege or punish student athletes
• how young people are socialized into the ideal of team cooperation
• differences between boys’ and girls’ participation in organized sports

We see that a single topic can be approached from many different perspectives depending on how the disciplinary boundaries are drawn and how the topic is framed. This step of the research process requires you to make some decisions early on to focus the topic on a manageable and appropriate scope for the rest of the strategy. ( Hansen & Paul, 2015 ).

‘The literature’ consists of the published works that document a scholarly conversation in a field of study. You will find, in ‘the literature,’ documents that explain the background of your topic so the reader knows where you found loose ends in the established research of the field and what led you to your own project.  Although your own literature review will focus on primary, peer-reviewed resources, it will begin by first grounding yourself in background subject information generally found in secondary and tertiary sources such as books and encyclopedias.  Once you have that essential overview, you delve into the seminal literature of the field. As a result, while your literature review may consist of research articles tightly focused on your topic with secondary and tertiary sources used more sparingly, all three types of information (primary, secondary, tertiary) are critical to your research.

2.1.2 Definitions

• Theoretical – discusses a theory, conceptual model or framework for understanding a problem.
• Empirical – applies theory to a behavior or event and reports derived data to findings.
• Seminal – “A classic work of research literature that is more than 5 years old and is marked by its uniqueness and contribution to professional knowledge.” ( Houser, 4th ed., 2018, p. 112 ).
• Practical – “…accounts of how things are done” ( Wallace & Wray, 3rd ed., 2016, p. 20 ). Action research, in Education, refers to a wide variety of methods used to develop practical solutions. ( Great Schools Partnership, 2017 ).
• Policy – generally produced by policy-makers, such as government agencies.
• Primary – published results of original research studies .
• Secondary – interpret, discuss, summarize original sources
• Tertiary – synthesize or distill primary and secondary sources.  Examples include: encyclopedias, directories, dictionaries, handbooks, guides, classification, chronology, and other fact books.
• Grey literature – research and information released by non-commercial publishers, such as government agencies, policy organizations, and think-tanks.

‘The literature’ is published in books, journal articles, conference proceedings, theses and dissertations.  It can also be found in newspapers, encyclopedias, textbooks, as well as websites and reports written by government agencies and professional organizations. While these formats may contain what we define as ‘the literature’, not all of it will be appropriate for inclusion in your own literature review.

These sources are found through different tools that we will discuss later in this section. Although a discovery tool, such as a database or catalog, may link you to the ‘the literature’ not every tool is appropriate to every literature review.  No single source will have all of the information resources you should consult.  A comprehensive literature review should include searches in the following:

• Multiple subject and article databases
• Library and other book catalogs
• Grey literature sources

2.2 Information Cycle

To get a better idea of how the literature in a discipline develops, it’s useful to see how the information publication lifecycle works.  These distinct stages show how information is created, reviewed, and distributed over time.

The following chart can be used to guide you in searching literature existing at various stages of the scholarly communication process (freely accessible sources are linked, subscription or subscribed sources are listed but not linked):

2.3 Information Types

To continue our discussion of information sources, there are two ways published information in the field can be categorized:

• Articles by the type of periodical in which an article it is published, for example, magazine, trade, or scholarly publications .
• Where the material is located in the information cycle, as in primary, secondary, or tertiary information sources .

2.3.1 Popular, Trade, or Scholarly publications

2.3.1.1 types of periodicals.

Journals, trade publications, and magazines are all periodicals, and articles from these publications they can all look similar article by article when you are searching in the databases. It is good to review the differences and think about when to use information from each type of periodical.

2.3.1.2 Magazines

A magazine is a collection of articles and images about diverse topics of popular interest and current events.

Features of magazines:

• articles are usually written by journalists
• articles are written for the average adult
• articles tend to be short
• articles rarely provides a list of reference sources at the end of the article
• lots of color images and advertisements
• the decision about what goes into the magazine is made by an editor or publisher
• magazines can have broad appeal, like Time and Newsweek , or a narrow focus, like Sports Illustrated and Mother Earth News .

Popular magazines like Psychology Today , Sports Illustrated , and Rolling Stone can be good sources for articles on recent events or pop-culture topics, while Harpers , Scientific American , and The New Republic will offer more in-depth articles on a wider range of subjects. These articles are geared towards readers who, although not experts, are knowledgeable about the issues presented.

2.3.1.3 Trade Publications

Trade publications or trade journals are periodicals directed to members of a specific profession. They often have information about industry trends and practical information for people working in the field.

Features of trade publications:

• Authors are specialists in their fields
• Focused on members of a specific industry or profession
• No peer review process
• Include photographs, illustrations, charts, and graphs, often in color
• Technical vocabulary

Trade publications are geared towards professionals in a discipline. They report news and trends in a field, but not original research. They may provide product or service reviews, job listings, and advertisements.

2.3.1.4 Scholarly, Academic, and Scientific Publications

Scholarly, academic, and scientific publications are a collections of articles written by scholars in an academic or professional field. Most journals are peer-reviewed or refereed, which means a panel of scholars reviews articles to decide if they should be accepted into a specific publication. Journal articles are the main source of information for researchers and for literature reviews.

Features of journals:

• written by scholars and subject experts
• author’ credentials and institution will be identified
• written for other scholars
• dedicated to a specific discipline that it covers in depth
• often report on original or innovative research
• long articles, often 5-15 pages or more
• articles almost always include a list of sources at the end (Works Cited, References, Sources, or Bibliography) that point back to where the information was derived
• no or very few advertisements
• published by organizations or associations to advance their specialized body of knowledge

Scholarly journals provider articles of interest to experts or researchers in a discipline. An editorial board of respected scholars (peers) reviews all articles submitted to a journal. They decide if the article provides a noteworthy contribution to the field and should be published. There are typically few  little or no advertisements. Articles published in scholarly journals will include a list of references.

2.3.1.5 A word about open access journals

Increasingly, scholars are publishing findings and original research in open access journals .   Open access journals are scholarly and peer-reviewed and open access publishers provide unrestricted access and unrestricted use.  Open access is a means of disseminating scholarly research that breaks from the traditional subscription model of academic publishing. It is free of charge to readers and because it is online, it is available at anytime, anywhere in the world, to anyone with access to the internet.  The Directory of Open Access Journals ( DOAJ ) indexes and provides access to high-quality, peer-reviewed scholarly articles.

In summary, newspapers and other popular press publications are useful for getting general topic ideas. Trade publications are useful for practical application in a profession and may also be a good source of keywords for future searching. Scholarly journals are the conversation of the scholars who are doing research in a specific discipline and publishing their research findings.

2.3.1.6 Primary, Secondary, and Tertiary Sources

Primary sources of information are those types of information that come first. Some examples of primary sources are:

• original research, like data from an experiment with plankton.
• diaries, journals, photographs
• data from the census bureau or a survey you have done
• original documents, like the constitution or a birth certificate
• newspapers are primary sources when they report current events or current opinion
• speeches, interviews, email, letters
• religious books
• personal memoirs and autobiographies
• pottery or weavings

There are different types of primary sources for different disciplines.  In the discipline of history, for example, a diary or transcript of a speech is a primary source.  In education and nursing, primary sources will generally be original research, including data sets.

Secondary sources are written about primary sources to interpret or analyze them. They are a step or more removed from the primary event or item. Some examples of secondary sources are:

• commentaries on speeches
• critiques of plays, journalism, or books
• a journal article that talks about a primary source such as an interpretation of Steinbeck’s The Grapes of Wrath, or the flower symbolism of Monet’s water garden paintings
• textbooks (can also be considered tertiary)
• biographies
• encyclopedias

Tertiary sources are further removed from the original material and are a distillation and collection of primary and secondary sources. Some examples are:

• bibliography of critical works about an author
• textbooks (also considered secondary)

A comparison of information sources across disciplines:

2.4 Information Sources

In this section, we discuss how to find not only information, but the sources of information in your discipline or topic area.  As we see in the graphic and chart above, the information you need for your literature review will be located in multiple places.  How and where research and publication occurs drives how and where the information is located, which in turn determines how you will discover and retrieve it.  When we talk about information sources for a literature review in education or nursing, we generally mean these five areas: the internet, reference material and other books, empirical or evidence-based articles in scholarly, peer-reviewed journals, conference proceedings and papers, dissertations and theses, and grey literature.

The World Wide Web can be an excellent place to satisfy some initial research needs.

• It is a good resource for background information and for finding keywords for searching in the library catalog and databases.
• It is a good tool for locating professional organizations and searching for information and the names of experts in a given discipline.
• Google Scholar is a useful discovery tool for citations, especially if you are trying to get the lay of the land surrounding your topic or if you are having a problem with keywords in the databases. You can find some information to refine your search terms. It is NOT acceptable to depend on Google Scholar for finding articles because of the spotty coverage and lack of adequate search features.

2.4.2 Books and Reference Sources

Reference materials and books are available in both print and electronic formats. They provide gateway knowledge to a subject area and are useful at the beginning of the research process to:

• Get an overview of the topic, learn the scope, key definitions, significant figures who are involved, and important timelines
• Discover the foundations of a topic
• Learn essential definitions, vocabulary terms, and keywords you can use in your literature searching strategy

2.4.3 Scholarly Articles in Journals

Another major category of information sources is scholarly information produced by subject experts working in academic institutions, research centers and scholarly organizations. Scholars and researchers generate information that advances our knowledge and understanding of the world. The research they do creates new opportunities for inventions, practical applications, and new approaches to solving problems or understanding issues.

Academics, researchers and students at universities make their contributions to scholarly knowledge available in many forms:

• masters’ theses
• doctoral dissertations
• conference papers
• journal articles and books
• individual scholars’ web pages
• web pages developed by the researcher’s’ home institution (Hansen & Paul, 2015).

Scholars and researchers introduce their discoveries to the world in a formal system of information dissemination that has developed over centuries. Because scholarly research undergoes a process of “peer review” before being published (meaning that other experts review the work and pass judgment about whether it is worthy of publication), the information you find from scholarly sources meets preset standards for accuracy, credibility and validity in that field.

Likewise, scholarly journal articles are generally considered to be among the most reliable sources of information because they have gone through a peer-review process.

2.4.5 Conference Papers & Proceedings

Conferences are a major source of  emerging research where researchers present papers on their current research and obtain feedback from the audience.  The papers presented in the conference are then usually published in a volume called a conference proceeding.  Conference proceedings highlight current discussion in a discipline and can lead you to scholars who are interested in specific research areas.

A word about conference papers: several factors contribute to making these documents difficult to find.  It may be months before a paper is published as a journal article, or it may never be published.  Publishers and professional associations are inconsistent in how they publish proceedings.  For example, the papers from an annual conference may be published as individual, stand-alone titles, which may be indexed in a library catalog, or the conference proceedings may be treated more like a periodical or serial and, therefore, indexed in a journal database.

It is not unusual that papers delivered at professional conferences are not published in print or electronic form, although an abstract may be available.  In these cases, the full paper may only be available from the author or authors.

The most important thing to remember is that if you have any difficulty finding a conference proceeding or paper, ask a librarian for assistance.

2.4.6 Dissertations and Theses

Dissertations and theses can be rich sources of information and have extensive reference lists to scan for resources. They are considered gray literature, so are not “peer reviewed”. The accuracy and validity of the paper itself may depend on the school that awarded the doctoral or master’s  degree to the author.

2.5 Conclusion

In thinking about ‘the literature’ of your discipline, you are beginning the first step in writing your own literature review.  By understanding what the literature in your field is, as well as how and when it is generated, you begin to know what is available and where to look for it.

We briefly discussed seven types of (sometimes overlapping) information:

• information found on the web
• information found in reference books and monographs
• information found in scholarly journals
• information found in conference proceedings and papers
• information found in dissertations and theses
• information found in magazines and trade journals
• information that is primary, secondary, or tertiary.

By conceptualizing or scoping how and where the literature of your discipline or topic area is generated, you have started on your way to writing your own literature review.

Finally, remember:

“All information sources are not created equal. Sources can vary greatly in terms of how carefully they are researched, written, edited, and reviewed for accuracy. Common sense will help you identify obviously questionable sources, such as tabloids that feature tales of alien abductions, or personal websites with glaring typos. Sometimes, however, a source’s reliability—or lack of it—is not so obvious…You will consider criteria such as the type of source, its intended purpose and audience, the author’s (or authors’) qualifications, the publication’s reputation, any indications of bias or hidden agendas, how current the source is, and the overall quality of the writing, thinking, and design.”  ( Writing for Success, 2015, p. 448 ).

We will cover how to evaluate sources in more detail in Chapter 5.

For each of these information needs, indicate what resources would be the best fit to answer your question. There may be more than one source so don’t feel like you have to limit yourself to only one. See Answer Key for the correct response.

• You are to write a brief paper on a theory that you only vaguely understand. You need some basic information. Where would you look?
• If you heard something on the radio about a recent research involving an herbal intervention for weight loss where could you find the actual study?
• You are going to be doing an internship in a group home for young men. You have heard that one issue that comes up for them is anger. Where would you look for practical interventions to help you manage this problem if it came up?
• You have the opportunity to work on a research project through a grant proposal. You need to justify the research question and show that there is an interest and a need for this research. What resources would you cite in your application?
• You have been assigned a project to find primary sources about classroom discipline used in early 20th-century schools. What primary sources could you use and where would you find them?
• You have an idea for a great thesis but you are afraid that it has been done before. Since you would like to do something original, where could you find out if someone else has done the project?
• There was a post on Facebook that welfare recipients in Arizona were recently tested for drug use with only three in 140,000 having positive results. Where can I find out if this number is accurate?

Test Yourself

Question 1  match the type of periodical to its content.

Trade publication Scholarly journal Magazine

• Contains articles about a variety of topics of popular interest; also contains advertising.
• Has information about industry trends and practical information for professionals in a field.
• Contains articles written by scholars in an academic field and reviewed by experts in that field.

Question 2: Given what you know about information types and sources, put the following information sources in order from the least accurate and reliable  to the most accurate and reliable. (1 least accurate/4 most accurate)

• Books and encyclopedias
• News broadcasts and social media directly following an event.
• Analysis of an event in the news media or popular magazine weeks after an event.
• Articles written by scholars and published in a journal.

Question 3: What is information called that is either a diary, a speech, original research, data, artwork, or a religious book.

Question 4: to find the best information in the databases you need to use keywords that are used by the scholars. where do you find out what keywords to try.

• From websites
• In journal articles
• All of the above

Question 5: Which of the following is NOT true about scholarly journals?

• They contain the conversation of the scholars on a particular subject.
• They are of interest to the general public.
• The articles are followed by an extensive reference list.
• They contain reports of original research.

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Literature Reviews for Education and Nursing Graduate Students Copyright © by Linda Frederiksen is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Literature Review Basics

• Primary & Secondary Sources
• Literature Review Introduction
• Writing Literature Reviews
• Tutorials & Samples

The Literature

The Literature refers to the collection of scholarly writings on a topic. This includes peer-reviewed articles, books, dissertations and conference papers.

• When reviewing the literature, be sure to include major works as well as studies that respond to major works. You will want to focus on primary sources, though secondary sources can be valuable as well.

Primary Sources

The term primary source is used broadly to embody all sources that are original. P rimary sources provide first-hand information that is closest to the object of study. Primary sources vary by discipline.

• In the natural and social sciences, original reports of research found in academic journals detailing the methodology used in the research, in-depth descriptions, and discussions of the findings are considered primary sources of information.
• Other common examples of primary sources include speeches, letters, diaries, autobiographies, interviews, official reports, court records, artifacts, photographs, and drawings.  

Galvan, J. L. (2013). Writing literature reviews: A guide for students of the social and behavioral sciences . Glendale, CA: Pyrczak.

Secondary Sources

A secondary source is a source that provides non-original or secondhand data or information. 

• Secondary sources are written about primary sources.
• Research summaries reported in textbooks, magazines, and newspapers are considered secondary sources. They typically provide global descriptions of results with few details on the methodology. Other examples of secondary sources include biographies and critical studies of an author's work.

Secondary Source. (2005). In W. Paul Vogt (Ed.), Dictionary of Statistics & Methodology. (3 rd ed., p. 291). Thousand Oaks, CA: SAGE Publications, Inc.

Weidenborner, S., & Caruso, D. (1997). Writing research papers: A guide to the process . New York: St. Martin's Press.

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Chapter 5: The Literature Review

5.3 Acceptable sources for literature reviews

Following are a few acceptable sources for literature reviews, listed in order from what will be considered most acceptable to less acceptable sources for your literature review assignments:

• Peer reviewed journal articles.
• Edited academic books.
• Articles in professional journals.
• Statistical data from government websites.
• Website material from professional associations (use sparingly and carefully). The following sections will explain and provide examples of these various sources.

Peer reviewed journal articles (papers)

A peer reviewed journal article is a paper that has been submitted to a scholarly journal, accepted, and published. Peer review journal papers go through a rigorous, blind review process of peer review. What this means is that two to three experts in the area of research featured in the paper have reviewed and accepted the paper for publication. The names of the author(s) who are seeking to publish the research have been removed (blind review), so as to minimize any bias towards the authors of the research (albeit, sometimes a savvy reviewer can discern who has done the research based upon previous publications, etc.). This blind review process can be long (often 12 to 18 months) and may involve many back and forth edits on the behalf of the researchers, as they work to address the edits and concerns of the peers who reviewed their paper. Often, reviewers will reject the paper for a variety of reasons, such as unclear or questionable methods, lack of contribution to the field, etc. Because peer reviewed journal articles have gone through a rigorous process of review, they are considered to be the premier source for research. Peer reviewed journal articles should serve as the foundation for your literature review.

The following link will provide more information on peer reviewed journal articles. Make sure you watch the little video on the upper left-hand side of your screen, in addition to reading the material at the following website:    http://guides.lib.jjay.cuny.edu/c.php?g=288333&p=1922599

Edited academic books

An edited academic book is a collection of scholarly scientific papers written by different authors. The works are original papers, not published elsewhere (“Edited volume,” 2018). The papers within the text also go through a process of review; however, the review is often not a blind review because the authors have been invited to contribute to the book. Consequently, edited academic books are fine to use for your literature review, but you also want to ensure that your literature review contains mostly peer reviewed journal papers.

Articles in professional journals

Articles from professional journals should be used with caution for your literature review. This is because articles in trade journals are not usually peer reviewed, even though they may appear to be. A good way to find out is to read the “About Us” section of the professional journal, which should state whether or not the papers are peer reviewed. You can also find out by Googling the name of the journal and adding “peer reviewed” to the search.

Statistical data from governmental websites

Governmental websites can be excellent sources for statistical data, e.g, Statistics Canada collects and publishes data related to the economy, society, and the environment (see https://www.statcan.gc.ca/eng/start ).

Website material from professional associations

Material from other websites can also serve as a source for statistics that you may need for your literature review. Since you want to justify the value of the research that interests you, you might make use of a professional association’s website to learn how many members they have, for example. You might want to demonstrate, as part of the introduction to your literature review, why more research on the topic of PTSD in police officers is important. You could use peer reviewed journal articles to determine the prevalence of PTSD in police officers in Canada in the last ten years, and then use the Ontario Police Officers´ Association website to determine the approximate number of police officers employed in the Province of Ontario over the last ten years. This might help you estimate how many police officers could be suffering with PTSD in Ontario. That number could potentially help to justify a research grant down the road. But again, this type of website- based material should be used with caution and sparingly.

Research Methods for the Social Sciences: An Introduction Copyright © 2020 by Valerie Sheppard is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Primary Sources: What They Are and Where to Find Them

What is a primary source.

• Finding Primary Sources in the UWRF Library

A primary source is an original object or document created during the time under study.   Primary sources vary by discipline and can include historical and legal documents, diaries, letters, family records, speeches, interviews, autobiographies, film, government documents, eye witness accounts, results of an experiment, statistical data, pieces of creative writing, and art objects. In the natural and social sciences, the results of an experiment or study are typically found in scholarly articles or papers delivered at conferences, so those articles and papers that present the original results are considered primary sources.  

A secondary source is something written about a primary source. Secondary sources include comments on, interpretations of, or discussions about the original material. You can think of secondary sources as second-hand information. If I tell you something, I am the primary source. If you tell someone else what I told you, you are the secondard source. Secondary source materials can be articles in newspapers or popular magazines, book or movie reviews, or articles found in scholarly journals that evaluate or criticize someone else's original research.

Research versus Review

Scientific and other peer reviewed journals are excellent sources for primary research sources. However, not every article in those journals will be an article with original research. Some will include book reviews and other materials that are more obviously secondary sources . More difficult to differentiate from original research articles are review articles . Both types of articles will end with a list of References (or Works Cited). Review articles are often as lengthy or even longer that original research articles. What the authors of review articles are doing is analysing and evaluating current research or investigations related to a specific topic, field, or problem. They are not primary sources since they review previously published material. They can be helpful for identifying potentially good primary sources, but they aren't primary themselves. Primary research articles can be identified by a commonly used format. If an article contains the following elements, you can count on it being a primary research article. Look for sections entitled Methods (sometimes with variations, such as Materials and Methods), Results (usually followed with charts and statistical tables), and Discussion . You can also read the abstract to get a good sense of the kind of article that is being presented. If it is a review article instead of a research article, the abstract should make that clear. If there is no abstract at all, that in itself may be a sign that it is not a primary resource. Short research articles, such as those found in Science and similar scientific publications that mix news, editorials, and forums with research reports, may not include any of those elements. In those cases look at the words the authors use, phrases such as "we tested," "we used," and "in our study, we measured" will tell you that the article is reporting on original research.

Primary or Secondary: You Decide

The distinction between types of sources can get tricky, because a secondary source may also be a primary source. DoVeanna Fulton's book on slave narratives, for example, can be looked at as both a secondary and a primary source. The distinction may depend on how you are using the source and the nature of your research. If you are researching slave narratives, the book would be a secondary source because Fulton is commenting on the narratives. If your assignment is to write a book review of Speaking Power , the book becomes a primary source, because you are commenting, evaluating, and discussing DoVeanna Fulton's ideas.

You can't always determine if something is primary or secondary just because of the source it is found in. Articles in newspapers and magazines are usually considered secondary sources. However, if a story in a newspaper about the Iraq war is an eyewitness account, that would be a primary source. If the reporter, however, includes additional materials he or she has gathered through interviews or other investigations, the article would be a secondary source. An interview in the Rolling Stone with Chris Robinson of the Black Crowes would be a primary source, but a review of the latest Black Crowes album would be a secondary source. In contrast, scholarly journals include research articles with primary materials, but they also have review articles that are not, or in some disciplines include articles where scholars are looking at primary source materials and coming to new conclusions.

For your thinking and not just to confuse you even further, some experts include tertiary sources as an additional distinction to make. These are sources that compile or, especially, digest other sources. Some reference materials and textbooks are considered tertiary sources when their chief purpose is to list or briefly summarize or, from an even further removed distance, repackage ideas. This is the reason that you may be advised not to include an encyclopedia article in a final bibliography.

The above material was adapted from the excellent explanation written by John Henderson found on Ithaca College's library website http://www.ithacalibrary.com/sp/subjects/primary and is used with permission.

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2.4: Primary, Secondary and Tertiary Sources

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Teaching & Learning and University Libraries

Another information category is called publication mode and has to do with whether the information is:

• Firsthand information (information in its original form, not translated or published in another form).
• Secondhand information (a restatement, analysis, or interpretation of original information).
• Thirdhand information (a summary or repackaging of original information, often based on secondary information that has been published).

The three labels for information sources in this category are, respectively, primary sources, secondary sources, and tertiary sources . Here are examples to illustrate the first- handedness, second-handedness, and third-handedness of information:

When you make distinctions between primary, secondary, and tertiary sources, you are relating the information itself to the context in which it was created. Understanding that relationship is an important skill that you’ll need in college, as well as in the workplace. Noting the relationship between creation and context helps us understand the “big picture” in which information operates and helps us figure out which information we can depend on. That’s a big part of thinking critically, a major benefit of actually becoming an educated person.

As a reminder, recall one of the frames of the Framework for Information Literacy is Authority is Constructed and Contextual . Information does not occur in a vacuum, but within a context that impacts its meaning. Part of that context will be how you as an information consumer will process the different facets in which that information exists. So, with this in mind, recognize that primary sources as defined below are not cut and dried, nor black or white. For example, to a historian, an image or a representation of a piece of sculpture might be considered a primary source for the purposes of historical analysis; however, to a sculpture or an archaeologist, anything short of the physical piece of sculpture itself would not be considered a primary source. So, in this case, the “context” to consider is how the source of information itself is perceived by a particular discipline (history vs. sculpture or archaeology). More on this below when we consider the “format” of a source.

Primary Sources – Because it is in its original form, the information in primary sources has reached us from its creators without going through any filter. We get it firsthand. Here are some examples that are often used as primary sources:

• Any literary work, including novels, plays, and poems.
• Breaking news (first formal documentation of event–remember the Information Cycle).
• Advertisements.
• Music and dance performances.
• Eyewitness accounts, including photographs and recorded interviews.
• Blog entries that are autobiographical.
• Scholarly blogs that provide data or are highly theoretical, even though they contain no autobiography.
• Artifacts such as tools, clothing, or other objects.
• Original documents such as tax returns, marriage licenses, and transcripts of trials.
• Websites, although many are secondary.
• Correspondence, including email.
• Records of organizations and government agencies.
• Journal articles that report original research for the first time (at least the parts about the new research, plus their data).

Secondary Source – These sources are sources about the sources, such as analysis or interpretation of the original information, the primary source. Thus, the information comes to us secondhand, or through at least one filter. Here are some examples that are often used as secondary sources:

• Nonfiction books and magazine articles except autobiography.
• An article or website that critiques a novel, play, painting, or piece of music.
• An article or web site that synthesizes expert opinion and several eyewitness accounts for a new understanding of an event.
• The literature review portion of a scholarly journal article.

Tertiary Source – These sources further repackage the original information because they index, condense, or summarize the original.

Typically, by the time tertiary sources are developed, there have been many secondary sources prepared on their subjects, and you can think of tertiary sources as information that comes to us “third-hand,” that is, pre -processed. Tertiary sources are usually publications that you are not intended to read from cover to cover but to dip in and out of for the information you need. You can think of them as a good place for background information to start your research but a bad place to end up. Here are some examples that are often used as tertiary sources, which are also considered “reference sources” in the library world:

• Dictionaries.
• Guide books, like the MLA Handbook
• Survey articles.
• Bibliographies.
• Encyclopedias, including Wikipedia.
• Most textbooks, including the one you are now reading.

Tertiary sources are usually not acceptable as cited sources in college research projects because they are so far removed from firsthand information. That’s why most professors don’t want you to use Wikipedia as a citable source: the information in Wikipedia is far from original information. Other people have considered it, decided what they think about it, rearranged it, and summarized it–all of which is actually what your professors want you , not another author, to do with information in your research projects.

The Details Are Tricky — A few things about primary or secondary sources might surprise you:

• Sources have the potential of becoming primary rather than always exist as primary sources.

It’s easy to think that it is the format of primary sources that makes them primary. But that’s not all that matters. When you see lists like the one above of sources that are often used as primary sources, it’s wise to remember that the ones listed are not automatically already primary sources. Firsthand sources get that designation only when researchers actually find their information relevant and use it.

For instance: Here is an illustration of the frame, Authority is Constructed and Contextual. Records that could be relevant to those studying government are created every day by federal, state, county, and city governments as they operate. But until the raw data are actually used by a researcher, they cannot be considered primary sources. How this data is used is what gives these sources the designation, and authority, as primary sources.

Another example that references the frame, Authority is Constructed and Contextual : A diary about his flying missions kept by an American helicopter pilot in the Vietnam War is not a primary source until, say, a researcher uses it in her study of how the war was carried out. But it will never be a primary source for a researcher studying the U.S. public’s reaction to the war because it does not contain information relevant to that study.

• Primary sources, even eyewitness accounts, are not necessarily accurate. Their accuracy has to be evaluated, just like that of all sources.
• Something that is usually considered a secondary source can be considered a primary source, depending on the research project and the context in which something is used .

Here is another example where the context of the use of the source dictates whether or not the source is primary or secondary. For instance, movie reviews are usually considered secondary sources. But if your research project is about the effect movie reviews have on ticket sales, the movie reviews you study would become primary sources.

• Deciding whether to consider a journal article a primary or a secondary source can be complicated for at least two reasons.

First, scholarly journal articles that report new research for the first time are usually based on data. So some disciplines consider the data to be the primary source, and the journal article that describes and analyzes them is considered a secondary source.

However, particularly in the sciences, the original researcher might find it difficult or impossible (he or she might not be allowed) to share the data. So sometimes you have nothing more firsthand than the journal article, which argues for calling it the relevant primary source because it’s the closest thing that exists to the data.

Second, even scholarly journal articles that announce new research for the first time usually contain more than data. They also typically contain secondary source elements, such as a literature review, bibliography, and sections on data analysis and interpretation. So they can actually be a mix of primary and secondary elements. Even so, in some disciplines, a journal article that announces new research findings for the first time is considered to be, as a whole, a primary source for the researchers using it.

ACTIVITY: Under What Circumstances?

Instructions: Look at each of the sources listed below and think of circumstances under which each could become a primary source. (There are probably many potential circumstances for each.) So just imagine you are a researcher with projects that would make each item firsthand information that is relevant to your work. What kind of project would make each of the following sources relevant firsthand information? Our answers are at the bottom of the page, but remember that there are many more–including the ones you think of that we didn’t!

• Fallingwater, a Pennsylvania home designed and constructed by Frank Lloyd Wright in the 1930s.
• Poet W.H. Auden’s elegy for Y.S. Yeats.
• An arrowhead made by (Florida) Seminole Native Americans but found at Flint Ridge outside Columbus, Ohio.
• E-mail between the U.S. ambassador to the United Nations, Nikki Haley, and her staff about North Korea.
• A marriage license.

Despite their fluidity, what primary sources usually offer is too good not to consider using because:

• They are original. This unfiltered, firsthand information is not available anywhere else.
• Their creator was a type of person unlike others in your research project, and you want to include that perspective.
• Their creator was present at an event and shares an eyewitness account.
• They are objects that existed at the particular time of the project you are studying.

Particularly in humanities courses, your professor may require you to use a certain number of primary sources for your project. In other courses, particularly in the sciences, you may be required to use only primary sources.

What is considered primary and secondary sources can vary from discipline to discipline. If you are required to use primary sources for your research project, before getting too deep into your project, check with your professor to make sure he or she agrees with your choices. After all, it’s your professor who will be grading your project. A librarian, too, can verify your choices. Just remember to take a copy of your assignment with you when you ask, because the librarian will want to see the original assignment. After all, that’s a primary source!

POSSIBLE AnswerS TO ACTIVITY: Under What Circumstances?

• You are doing a study of the entrances Wright designed for homes, which were smaller than other architects of the time typically designed entrances.
• Your research project is about the Auden-Yeats relationship.
• Your research project is about trade among 19th century Native Americans east of the Mississippi River.
• Your research project is on how Ambassador Haley conveyed a decision about North Korea to her staff.
• You are writing about the life of a person who claimed to have married several times, and you need more than her statements about when those marriages took place and to whom.

• Primary Sources
• Primary Source Repositories @ USC
• Large Primary Source Databases
• Newspapers & Magazines
• Topical Primary Source Collections
• Visual Primary Source Collections
• Multimedia Primary Source Collections
• Electronically available Rare Books & Rare Book Collections
• Electronically available Maps
• Electronically available Manuscripts
• Search Strategies

Evaluating Primary Sources

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• Teaching with Primary Sources

It is important to examine primary sources with a critical eye since they represent unfiltered records of the past. Below are some questions to consider once you've found a primary source(s):

RUSA's Guide to Evaluating Primary Sources : 

• Who is the author or creator?
• ​What biases or assumptions may have influenced the author or creator?
• Who was the intended audience?
• What is the origin of the primary source?
• What was the significance of the source at the time it was created?
• Has the source been edited or translated, or altered in some way from the original?
• What questions could be answered about the time period by using this source?
• What, if any, are the limitations of the source?
• Does your understanding of the source fit with other scholars’ interpretations, or does it challenge their argument?

The 6 C's of Primary Source Analysis :

• Content - What is the main idea? Describe in detail what you see
• Citation  - When was this created?
• Context  - What is going on in the world, the country, the region, or the locality when this was created?
• Connections - Link the primary source to other things that you already know or have learned about.
• Communication - Is this source reliable?
• Conclusions - Ask yourself: How does the primary source contribute to our understanding of history?

Additional Resources

Research Guide: Primary Sources at Yale

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Lau F, Kuziemsky C, editors. Handbook of eHealth Evaluation: An Evidence-based Approach [Internet]. Victoria (BC): University of Victoria; 2017 Feb 27.

Handbook of eHealth Evaluation: An Evidence-based Approach [Internet].

Chapter 9 methods for literature reviews.

Guy Paré and Spyros Kitsiou .

9.1. Introduction

Literature reviews play a critical role in scholarship because science remains, first and foremost, a cumulative endeavour ( vom Brocke et al., 2009 ). As in any academic discipline, rigorous knowledge syntheses are becoming indispensable in keeping up with an exponentially growing eHealth literature, assisting practitioners, academics, and graduate students in finding, evaluating, and synthesizing the contents of many empirical and conceptual papers. Among other methods, literature reviews are essential for: (a) identifying what has been written on a subject or topic; (b) determining the extent to which a specific research area reveals any interpretable trends or patterns; (c) aggregating empirical findings related to a narrow research question to support evidence-based practice; (d) generating new frameworks and theories; and (e) identifying topics or questions requiring more investigation ( Paré, Trudel, Jaana, & Kitsiou, 2015 ).

Literature reviews can take two major forms. The most prevalent one is the “literature review” or “background” section within a journal paper or a chapter in a graduate thesis. This section synthesizes the extant literature and usually identifies the gaps in knowledge that the empirical study addresses ( Sylvester, Tate, & Johnstone, 2013 ). It may also provide a theoretical foundation for the proposed study, substantiate the presence of the research problem, justify the research as one that contributes something new to the cumulated knowledge, or validate the methods and approaches for the proposed study ( Hart, 1998 ; Levy & Ellis, 2006 ).

The second form of literature review, which is the focus of this chapter, constitutes an original and valuable work of research in and of itself ( Paré et al., 2015 ). Rather than providing a base for a researcher’s own work, it creates a solid starting point for all members of the community interested in a particular area or topic ( Mulrow, 1987 ). The so-called “review article” is a journal-length paper which has an overarching purpose to synthesize the literature in a field, without collecting or analyzing any primary data ( Green, Johnson, & Adams, 2006 ).

When appropriately conducted, review articles represent powerful information sources for practitioners looking for state-of-the art evidence to guide their decision-making and work practices ( Paré et al., 2015 ). Further, high-quality reviews become frequently cited pieces of work which researchers seek out as a first clear outline of the literature when undertaking empirical studies ( Cooper, 1988 ; Rowe, 2014 ). Scholars who track and gauge the impact of articles have found that review papers are cited and downloaded more often than any other type of published article ( Cronin, Ryan, & Coughlan, 2008 ; Montori, Wilczynski, Morgan, Haynes, & Hedges, 2003 ; Patsopoulos, Analatos, & Ioannidis, 2005 ). The reason for their popularity may be the fact that reading the review enables one to have an overview, if not a detailed knowledge of the area in question, as well as references to the most useful primary sources ( Cronin et al., 2008 ). Although they are not easy to conduct, the commitment to complete a review article provides a tremendous service to one’s academic community ( Paré et al., 2015 ; Petticrew & Roberts, 2006 ). Most, if not all, peer-reviewed journals in the fields of medical informatics publish review articles of some type.

The main objectives of this chapter are fourfold: (a) to provide an overview of the major steps and activities involved in conducting a stand-alone literature review; (b) to describe and contrast the different types of review articles that can contribute to the eHealth knowledge base; (c) to illustrate each review type with one or two examples from the eHealth literature; and (d) to provide a series of recommendations for prospective authors of review articles in this domain.

9.2. Overview of the Literature Review Process and Steps

As explained in Templier and Paré (2015) , there are six generic steps involved in conducting a review article:

• formulating the research question(s) and objective(s),
• searching the extant literature,
• screening for inclusion,
• assessing the quality of primary studies,
• extracting data, and
• analyzing data.

Although these steps are presented here in sequential order, one must keep in mind that the review process can be iterative and that many activities can be initiated during the planning stage and later refined during subsequent phases ( Finfgeld-Connett & Johnson, 2013 ; Kitchenham & Charters, 2007 ).

Formulating the research question(s) and objective(s): As a first step, members of the review team must appropriately justify the need for the review itself ( Petticrew & Roberts, 2006 ), identify the review’s main objective(s) ( Okoli & Schabram, 2010 ), and define the concepts or variables at the heart of their synthesis ( Cooper & Hedges, 2009 ; Webster & Watson, 2002 ). Importantly, they also need to articulate the research question(s) they propose to investigate ( Kitchenham & Charters, 2007 ). In this regard, we concur with Jesson, Matheson, and Lacey (2011) that clearly articulated research questions are key ingredients that guide the entire review methodology; they underscore the type of information that is needed, inform the search for and selection of relevant literature, and guide or orient the subsequent analysis. Searching the extant literature: The next step consists of searching the literature and making decisions about the suitability of material to be considered in the review ( Cooper, 1988 ). There exist three main coverage strategies. First, exhaustive coverage means an effort is made to be as comprehensive as possible in order to ensure that all relevant studies, published and unpublished, are included in the review and, thus, conclusions are based on this all-inclusive knowledge base. The second type of coverage consists of presenting materials that are representative of most other works in a given field or area. Often authors who adopt this strategy will search for relevant articles in a small number of top-tier journals in a field ( Paré et al., 2015 ). In the third strategy, the review team concentrates on prior works that have been central or pivotal to a particular topic. This may include empirical studies or conceptual papers that initiated a line of investigation, changed how problems or questions were framed, introduced new methods or concepts, or engendered important debate ( Cooper, 1988 ). Screening for inclusion: The following step consists of evaluating the applicability of the material identified in the preceding step ( Levy & Ellis, 2006 ; vom Brocke et al., 2009 ). Once a group of potential studies has been identified, members of the review team must screen them to determine their relevance ( Petticrew & Roberts, 2006 ). A set of predetermined rules provides a basis for including or excluding certain studies. This exercise requires a significant investment on the part of researchers, who must ensure enhanced objectivity and avoid biases or mistakes. As discussed later in this chapter, for certain types of reviews there must be at least two independent reviewers involved in the screening process and a procedure to resolve disagreements must also be in place ( Liberati et al., 2009 ; Shea et al., 2009 ). Assessing the quality of primary studies: In addition to screening material for inclusion, members of the review team may need to assess the scientific quality of the selected studies, that is, appraise the rigour of the research design and methods. Such formal assessment, which is usually conducted independently by at least two coders, helps members of the review team refine which studies to include in the final sample, determine whether or not the differences in quality may affect their conclusions, or guide how they analyze the data and interpret the findings ( Petticrew & Roberts, 2006 ). Ascribing quality scores to each primary study or considering through domain-based evaluations which study components have or have not been designed and executed appropriately makes it possible to reflect on the extent to which the selected study addresses possible biases and maximizes validity ( Shea et al., 2009 ). Extracting data: The following step involves gathering or extracting applicable information from each primary study included in the sample and deciding what is relevant to the problem of interest ( Cooper & Hedges, 2009 ). Indeed, the type of data that should be recorded mainly depends on the initial research questions ( Okoli & Schabram, 2010 ). However, important information may also be gathered about how, when, where and by whom the primary study was conducted, the research design and methods, or qualitative/quantitative results ( Cooper & Hedges, 2009 ). Analyzing and synthesizing data : As a final step, members of the review team must collate, summarize, aggregate, organize, and compare the evidence extracted from the included studies. The extracted data must be presented in a meaningful way that suggests a new contribution to the extant literature ( Jesson et al., 2011 ). Webster and Watson (2002) warn researchers that literature reviews should be much more than lists of papers and should provide a coherent lens to make sense of extant knowledge on a given topic. There exist several methods and techniques for synthesizing quantitative (e.g., frequency analysis, meta-analysis) and qualitative (e.g., grounded theory, narrative analysis, meta-ethnography) evidence ( Dixon-Woods, Agarwal, Jones, Young, & Sutton, 2005 ; Thomas & Harden, 2008 ).

9.3. Types of Review Articles and Brief Illustrations

EHealth researchers have at their disposal a number of approaches and methods for making sense out of existing literature, all with the purpose of casting current research findings into historical contexts or explaining contradictions that might exist among a set of primary research studies conducted on a particular topic. Our classification scheme is largely inspired from Paré and colleagues’ (2015) typology. Below we present and illustrate those review types that we feel are central to the growth and development of the eHealth domain.

9.3.1. Narrative Reviews

The narrative review is the “traditional” way of reviewing the extant literature and is skewed towards a qualitative interpretation of prior knowledge ( Sylvester et al., 2013 ). Put simply, a narrative review attempts to summarize or synthesize what has been written on a particular topic but does not seek generalization or cumulative knowledge from what is reviewed ( Davies, 2000 ; Green et al., 2006 ). Instead, the review team often undertakes the task of accumulating and synthesizing the literature to demonstrate the value of a particular point of view ( Baumeister & Leary, 1997 ). As such, reviewers may selectively ignore or limit the attention paid to certain studies in order to make a point. In this rather unsystematic approach, the selection of information from primary articles is subjective, lacks explicit criteria for inclusion and can lead to biased interpretations or inferences ( Green et al., 2006 ). There are several narrative reviews in the particular eHealth domain, as in all fields, which follow such an unstructured approach ( Silva et al., 2015 ; Paul et al., 2015 ).

Despite these criticisms, this type of review can be very useful in gathering together a volume of literature in a specific subject area and synthesizing it. As mentioned above, its primary purpose is to provide the reader with a comprehensive background for understanding current knowledge and highlighting the significance of new research ( Cronin et al., 2008 ). Faculty like to use narrative reviews in the classroom because they are often more up to date than textbooks, provide a single source for students to reference, and expose students to peer-reviewed literature ( Green et al., 2006 ). For researchers, narrative reviews can inspire research ideas by identifying gaps or inconsistencies in a body of knowledge, thus helping researchers to determine research questions or formulate hypotheses. Importantly, narrative reviews can also be used as educational articles to bring practitioners up to date with certain topics of issues ( Green et al., 2006 ).

Recently, there have been several efforts to introduce more rigour in narrative reviews that will elucidate common pitfalls and bring changes into their publication standards. Information systems researchers, among others, have contributed to advancing knowledge on how to structure a “traditional” review. For instance, Levy and Ellis (2006) proposed a generic framework for conducting such reviews. Their model follows the systematic data processing approach comprised of three steps, namely: (a) literature search and screening; (b) data extraction and analysis; and (c) writing the literature review. They provide detailed and very helpful instructions on how to conduct each step of the review process. As another methodological contribution, vom Brocke et al. (2009) offered a series of guidelines for conducting literature reviews, with a particular focus on how to search and extract the relevant body of knowledge. Last, Bandara, Miskon, and Fielt (2011) proposed a structured, predefined and tool-supported method to identify primary studies within a feasible scope, extract relevant content from identified articles, synthesize and analyze the findings, and effectively write and present the results of the literature review. We highly recommend that prospective authors of narrative reviews consult these useful sources before embarking on their work.

Darlow and Wen (2015) provide a good example of a highly structured narrative review in the eHealth field. These authors synthesized published articles that describe the development process of mobile health ( m-health ) interventions for patients’ cancer care self-management. As in most narrative reviews, the scope of the research questions being investigated is broad: (a) how development of these systems are carried out; (b) which methods are used to investigate these systems; and (c) what conclusions can be drawn as a result of the development of these systems. To provide clear answers to these questions, a literature search was conducted on six electronic databases and Google Scholar . The search was performed using several terms and free text words, combining them in an appropriate manner. Four inclusion and three exclusion criteria were utilized during the screening process. Both authors independently reviewed each of the identified articles to determine eligibility and extract study information. A flow diagram shows the number of studies identified, screened, and included or excluded at each stage of study selection. In terms of contributions, this review provides a series of practical recommendations for m-health intervention development.

9.3.2. Descriptive or Mapping Reviews

The primary goal of a descriptive review is to determine the extent to which a body of knowledge in a particular research topic reveals any interpretable pattern or trend with respect to pre-existing propositions, theories, methodologies or findings ( King & He, 2005 ; Paré et al., 2015 ). In contrast with narrative reviews, descriptive reviews follow a systematic and transparent procedure, including searching, screening and classifying studies ( Petersen, Vakkalanka, & Kuzniarz, 2015 ). Indeed, structured search methods are used to form a representative sample of a larger group of published works ( Paré et al., 2015 ). Further, authors of descriptive reviews extract from each study certain characteristics of interest, such as publication year, research methods, data collection techniques, and direction or strength of research outcomes (e.g., positive, negative, or non-significant) in the form of frequency analysis to produce quantitative results ( Sylvester et al., 2013 ). In essence, each study included in a descriptive review is treated as the unit of analysis and the published literature as a whole provides a database from which the authors attempt to identify any interpretable trends or draw overall conclusions about the merits of existing conceptualizations, propositions, methods or findings ( Paré et al., 2015 ). In doing so, a descriptive review may claim that its findings represent the state of the art in a particular domain ( King & He, 2005 ).

In the fields of health sciences and medical informatics, reviews that focus on examining the range, nature and evolution of a topic area are described by Anderson, Allen, Peckham, and Goodwin (2008) as mapping reviews . Like descriptive reviews, the research questions are generic and usually relate to publication patterns and trends. There is no preconceived plan to systematically review all of the literature although this can be done. Instead, researchers often present studies that are representative of most works published in a particular area and they consider a specific time frame to be mapped.

An example of this approach in the eHealth domain is offered by DeShazo, Lavallie, and Wolf (2009). The purpose of this descriptive or mapping review was to characterize publication trends in the medical informatics literature over a 20-year period (1987 to 2006). To achieve this ambitious objective, the authors performed a bibliometric analysis of medical informatics citations indexed in medline using publication trends, journal frequencies, impact factors, Medical Subject Headings (MeSH) term frequencies, and characteristics of citations. Findings revealed that there were over 77,000 medical informatics articles published during the covered period in numerous journals and that the average annual growth rate was 12%. The MeSH term analysis also suggested a strong interdisciplinary trend. Finally, average impact scores increased over time with two notable growth periods. Overall, patterns in research outputs that seem to characterize the historic trends and current components of the field of medical informatics suggest it may be a maturing discipline (DeShazo et al., 2009).

9.3.3. Scoping Reviews

Scoping reviews attempt to provide an initial indication of the potential size and nature of the extant literature on an emergent topic (Arksey & O’Malley, 2005; Daudt, van Mossel, & Scott, 2013 ; Levac, Colquhoun, & O’Brien, 2010). A scoping review may be conducted to examine the extent, range and nature of research activities in a particular area, determine the value of undertaking a full systematic review (discussed next), or identify research gaps in the extant literature ( Paré et al., 2015 ). In line with their main objective, scoping reviews usually conclude with the presentation of a detailed research agenda for future works along with potential implications for both practice and research.

Unlike narrative and descriptive reviews, the whole point of scoping the field is to be as comprehensive as possible, including grey literature (Arksey & O’Malley, 2005). Inclusion and exclusion criteria must be established to help researchers eliminate studies that are not aligned with the research questions. It is also recommended that at least two independent coders review abstracts yielded from the search strategy and then the full articles for study selection ( Daudt et al., 2013 ). The synthesized evidence from content or thematic analysis is relatively easy to present in tabular form (Arksey & O’Malley, 2005; Thomas & Harden, 2008 ).

One of the most highly cited scoping reviews in the eHealth domain was published by Archer, Fevrier-Thomas, Lokker, McKibbon, and Straus (2011) . These authors reviewed the existing literature on personal health record ( phr ) systems including design, functionality, implementation, applications, outcomes, and benefits. Seven databases were searched from 1985 to March 2010. Several search terms relating to phr s were used during this process. Two authors independently screened titles and abstracts to determine inclusion status. A second screen of full-text articles, again by two independent members of the research team, ensured that the studies described phr s. All in all, 130 articles met the criteria and their data were extracted manually into a database. The authors concluded that although there is a large amount of survey, observational, cohort/panel, and anecdotal evidence of phr benefits and satisfaction for patients, more research is needed to evaluate the results of phr implementations. Their in-depth analysis of the literature signalled that there is little solid evidence from randomized controlled trials or other studies through the use of phr s. Hence, they suggested that more research is needed that addresses the current lack of understanding of optimal functionality and usability of these systems, and how they can play a beneficial role in supporting patient self-management ( Archer et al., 2011 ).

9.3.4. Forms of Aggregative Reviews

Healthcare providers, practitioners, and policy-makers are nowadays overwhelmed with large volumes of information, including research-based evidence from numerous clinical trials and evaluation studies, assessing the effectiveness of health information technologies and interventions ( Ammenwerth & de Keizer, 2004 ; Deshazo et al., 2009 ). It is unrealistic to expect that all these disparate actors will have the time, skills, and necessary resources to identify the available evidence in the area of their expertise and consider it when making decisions. Systematic reviews that involve the rigorous application of scientific strategies aimed at limiting subjectivity and bias (i.e., systematic and random errors) can respond to this challenge.

Systematic reviews attempt to aggregate, appraise, and synthesize in a single source all empirical evidence that meet a set of previously specified eligibility criteria in order to answer a clearly formulated and often narrow research question on a particular topic of interest to support evidence-based practice ( Liberati et al., 2009 ). They adhere closely to explicit scientific principles ( Liberati et al., 2009 ) and rigorous methodological guidelines (Higgins & Green, 2008) aimed at reducing random and systematic errors that can lead to deviations from the truth in results or inferences. The use of explicit methods allows systematic reviews to aggregate a large body of research evidence, assess whether effects or relationships are in the same direction and of the same general magnitude, explain possible inconsistencies between study results, and determine the strength of the overall evidence for every outcome of interest based on the quality of included studies and the general consistency among them ( Cook, Mulrow, & Haynes, 1997 ). The main procedures of a systematic review involve:

• Formulating a review question and developing a search strategy based on explicit inclusion criteria for the identification of eligible studies (usually described in the context of a detailed review protocol).
• Searching for eligible studies using multiple databases and information sources, including grey literature sources, without any language restrictions.
• Selecting studies, extracting data, and assessing risk of bias in a duplicate manner using two independent reviewers to avoid random or systematic errors in the process.
• Analyzing data using quantitative or qualitative methods.
• Presenting results in summary of findings tables.
• Interpreting results and drawing conclusions.

Many systematic reviews, but not all, use statistical methods to combine the results of independent studies into a single quantitative estimate or summary effect size. Known as meta-analyses , these reviews use specific data extraction and statistical techniques (e.g., network, frequentist, or Bayesian meta-analyses) to calculate from each study by outcome of interest an effect size along with a confidence interval that reflects the degree of uncertainty behind the point estimate of effect ( Borenstein, Hedges, Higgins, & Rothstein, 2009 ; Deeks, Higgins, & Altman, 2008 ). Subsequently, they use fixed or random-effects analysis models to combine the results of the included studies, assess statistical heterogeneity, and calculate a weighted average of the effect estimates from the different studies, taking into account their sample sizes. The summary effect size is a value that reflects the average magnitude of the intervention effect for a particular outcome of interest or, more generally, the strength of a relationship between two variables across all studies included in the systematic review. By statistically combining data from multiple studies, meta-analyses can create more precise and reliable estimates of intervention effects than those derived from individual studies alone, when these are examined independently as discrete sources of information.

The review by Gurol-Urganci, de Jongh, Vodopivec-Jamsek, Atun, and Car (2013) on the effects of mobile phone messaging reminders for attendance at healthcare appointments is an illustrative example of a high-quality systematic review with meta-analysis. Missed appointments are a major cause of inefficiency in healthcare delivery with substantial monetary costs to health systems. These authors sought to assess whether mobile phone-based appointment reminders delivered through Short Message Service ( sms ) or Multimedia Messaging Service ( mms ) are effective in improving rates of patient attendance and reducing overall costs. To this end, they conducted a comprehensive search on multiple databases using highly sensitive search strategies without language or publication-type restrictions to identify all rct s that are eligible for inclusion. In order to minimize the risk of omitting eligible studies not captured by the original search, they supplemented all electronic searches with manual screening of trial registers and references contained in the included studies. Study selection, data extraction, and risk of bias assessments were performed inde­­pen­dently by two coders using standardized methods to ensure consistency and to eliminate potential errors. Findings from eight rct s involving 6,615 participants were pooled into meta-analyses to calculate the magnitude of effects that mobile text message reminders have on the rate of attendance at healthcare appointments compared to no reminders and phone call reminders.

Meta-analyses are regarded as powerful tools for deriving meaningful conclusions. However, there are situations in which it is neither reasonable nor appropriate to pool studies together using meta-analytic methods simply because there is extensive clinical heterogeneity between the included studies or variation in measurement tools, comparisons, or outcomes of interest. In these cases, systematic reviews can use qualitative synthesis methods such as vote counting, content analysis, classification schemes and tabulations, as an alternative approach to narratively synthesize the results of the independent studies included in the review. This form of review is known as qualitative systematic review.

A rigorous example of one such review in the eHealth domain is presented by Mickan, Atherton, Roberts, Heneghan, and Tilson (2014) on the use of handheld computers by healthcare professionals and their impact on access to information and clinical decision-making. In line with the methodological guide­lines for systematic reviews, these authors: (a) developed and registered with prospero ( www.crd.york.ac.uk/ prospero / ) an a priori review protocol; (b) conducted comprehensive searches for eligible studies using multiple databases and other supplementary strategies (e.g., forward searches); and (c) subsequently carried out study selection, data extraction, and risk of bias assessments in a duplicate manner to eliminate potential errors in the review process. Heterogeneity between the included studies in terms of reported outcomes and measures precluded the use of meta-analytic methods. To this end, the authors resorted to using narrative analysis and synthesis to describe the effectiveness of handheld computers on accessing information for clinical knowledge, adherence to safety and clinical quality guidelines, and diagnostic decision-making.

In recent years, the number of systematic reviews in the field of health informatics has increased considerably. Systematic reviews with discordant findings can cause great confusion and make it difficult for decision-makers to interpret the review-level evidence ( Moher, 2013 ). Therefore, there is a growing need for appraisal and synthesis of prior systematic reviews to ensure that decision-making is constantly informed by the best available accumulated evidence. Umbrella reviews , also known as overviews of systematic reviews, are tertiary types of evidence synthesis that aim to accomplish this; that is, they aim to compare and contrast findings from multiple systematic reviews and meta-analyses ( Becker & Oxman, 2008 ). Umbrella reviews generally adhere to the same principles and rigorous methodological guidelines used in systematic reviews. However, the unit of analysis in umbrella reviews is the systematic review rather than the primary study ( Becker & Oxman, 2008 ). Unlike systematic reviews that have a narrow focus of inquiry, umbrella reviews focus on broader research topics for which there are several potential interventions ( Smith, Devane, Begley, & Clarke, 2011 ). A recent umbrella review on the effects of home telemonitoring interventions for patients with heart failure critically appraised, compared, and synthesized evidence from 15 systematic reviews to investigate which types of home telemonitoring technologies and forms of interventions are more effective in reducing mortality and hospital admissions ( Kitsiou, Paré, & Jaana, 2015 ).

9.3.5. Realist Reviews

Realist reviews are theory-driven interpretative reviews developed to inform, enhance, or supplement conventional systematic reviews by making sense of heterogeneous evidence about complex interventions applied in diverse contexts in a way that informs policy decision-making ( Greenhalgh, Wong, Westhorp, & Pawson, 2011 ). They originated from criticisms of positivist systematic reviews which centre on their “simplistic” underlying assumptions ( Oates, 2011 ). As explained above, systematic reviews seek to identify causation. Such logic is appropriate for fields like medicine and education where findings of randomized controlled trials can be aggregated to see whether a new treatment or intervention does improve outcomes. However, many argue that it is not possible to establish such direct causal links between interventions and outcomes in fields such as social policy, management, and information systems where for any intervention there is unlikely to be a regular or consistent outcome ( Oates, 2011 ; Pawson, 2006 ; Rousseau, Manning, & Denyer, 2008 ).

To circumvent these limitations, Pawson, Greenhalgh, Harvey, and Walshe (2005) have proposed a new approach for synthesizing knowledge that seeks to unpack the mechanism of how “complex interventions” work in particular contexts. The basic research question — what works? — which is usually associated with systematic reviews changes to: what is it about this intervention that works, for whom, in what circumstances, in what respects and why? Realist reviews have no particular preference for either quantitative or qualitative evidence. As a theory-building approach, a realist review usually starts by articulating likely underlying mechanisms and then scrutinizes available evidence to find out whether and where these mechanisms are applicable ( Shepperd et al., 2009 ). Primary studies found in the extant literature are viewed as case studies which can test and modify the initial theories ( Rousseau et al., 2008 ).

The main objective pursued in the realist review conducted by Otte-Trojel, de Bont, Rundall, and van de Klundert (2014) was to examine how patient portals contribute to health service delivery and patient outcomes. The specific goals were to investigate how outcomes are produced and, most importantly, how variations in outcomes can be explained. The research team started with an exploratory review of background documents and research studies to identify ways in which patient portals may contribute to health service delivery and patient outcomes. The authors identified six main ways which represent “educated guesses” to be tested against the data in the evaluation studies. These studies were identified through a formal and systematic search in four databases between 2003 and 2013. Two members of the research team selected the articles using a pre-established list of inclusion and exclusion criteria and following a two-step procedure. The authors then extracted data from the selected articles and created several tables, one for each outcome category. They organized information to bring forward those mechanisms where patient portals contribute to outcomes and the variation in outcomes across different contexts.

9.3.6. Critical Reviews

Lastly, critical reviews aim to provide a critical evaluation and interpretive analysis of existing literature on a particular topic of interest to reveal strengths, weaknesses, contradictions, controversies, inconsistencies, and/or other important issues with respect to theories, hypotheses, research methods or results ( Baumeister & Leary, 1997 ; Kirkevold, 1997 ). Unlike other review types, critical reviews attempt to take a reflective account of the research that has been done in a particular area of interest, and assess its credibility by using appraisal instruments or critical interpretive methods. In this way, critical reviews attempt to constructively inform other scholars about the weaknesses of prior research and strengthen knowledge development by giving focus and direction to studies for further improvement ( Kirkevold, 1997 ).

Kitsiou, Paré, and Jaana (2013) provide an example of a critical review that assessed the methodological quality of prior systematic reviews of home telemonitoring studies for chronic patients. The authors conducted a comprehensive search on multiple databases to identify eligible reviews and subsequently used a validated instrument to conduct an in-depth quality appraisal. Results indicate that the majority of systematic reviews in this particular area suffer from important methodological flaws and biases that impair their internal validity and limit their usefulness for clinical and decision-making purposes. To this end, they provide a number of recommendations to strengthen knowledge development towards improving the design and execution of future reviews on home telemonitoring.

9.4. Summary

Table 9.1 outlines the main types of literature reviews that were described in the previous sub-sections and summarizes the main characteristics that distinguish one review type from another. It also includes key references to methodological guidelines and useful sources that can be used by eHealth scholars and researchers for planning and developing reviews.

Typology of Literature Reviews (adapted from Paré et al., 2015).

As shown in Table 9.1 , each review type addresses different kinds of research questions or objectives, which subsequently define and dictate the methods and approaches that need to be used to achieve the overarching goal(s) of the review. For example, in the case of narrative reviews, there is greater flexibility in searching and synthesizing articles ( Green et al., 2006 ). Researchers are often relatively free to use a diversity of approaches to search, identify, and select relevant scientific articles, describe their operational characteristics, present how the individual studies fit together, and formulate conclusions. On the other hand, systematic reviews are characterized by their high level of systematicity, rigour, and use of explicit methods, based on an “a priori” review plan that aims to minimize bias in the analysis and synthesis process (Higgins & Green, 2008). Some reviews are exploratory in nature (e.g., scoping/mapping reviews), whereas others may be conducted to discover patterns (e.g., descriptive reviews) or involve a synthesis approach that may include the critical analysis of prior research ( Paré et al., 2015 ). Hence, in order to select the most appropriate type of review, it is critical to know before embarking on a review project, why the research synthesis is conducted and what type of methods are best aligned with the pursued goals.

9.5. Concluding Remarks

In light of the increased use of evidence-based practice and research generating stronger evidence ( Grady et al., 2011 ; Lyden et al., 2013 ), review articles have become essential tools for summarizing, synthesizing, integrating or critically appraising prior knowledge in the eHealth field. As mentioned earlier, when rigorously conducted review articles represent powerful information sources for eHealth scholars and practitioners looking for state-of-the-art evidence. The typology of literature reviews we used herein will allow eHealth researchers, graduate students and practitioners to gain a better understanding of the similarities and differences between review types.

We must stress that this classification scheme does not privilege any specific type of review as being of higher quality than another ( Paré et al., 2015 ). As explained above, each type of review has its own strengths and limitations. Having said that, we realize that the methodological rigour of any review — be it qualitative, quantitative or mixed — is a critical aspect that should be considered seriously by prospective authors. In the present context, the notion of rigour refers to the reliability and validity of the review process described in section 9.2. For one thing, reliability is related to the reproducibility of the review process and steps, which is facilitated by a comprehensive documentation of the literature search process, extraction, coding and analysis performed in the review. Whether the search is comprehensive or not, whether it involves a methodical approach for data extraction and synthesis or not, it is important that the review documents in an explicit and transparent manner the steps and approach that were used in the process of its development. Next, validity characterizes the degree to which the review process was conducted appropriately. It goes beyond documentation and reflects decisions related to the selection of the sources, the search terms used, the period of time covered, the articles selected in the search, and the application of backward and forward searches ( vom Brocke et al., 2009 ). In short, the rigour of any review article is reflected by the explicitness of its methods (i.e., transparency) and the soundness of the approach used. We refer those interested in the concepts of rigour and quality to the work of Templier and Paré (2015) which offers a detailed set of methodological guidelines for conducting and evaluating various types of review articles.

To conclude, our main objective in this chapter was to demystify the various types of literature reviews that are central to the continuous development of the eHealth field. It is our hope that our descriptive account will serve as a valuable source for those conducting, evaluating or using reviews in this important and growing domain.

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This publication is licensed under a Creative Commons License, Attribution-Noncommercial 4.0 International License (CC BY-NC 4.0): see https://creativecommons.org/licenses/by-nc/4.0/

• Cite this Page Paré G, Kitsiou S. Chapter 9 Methods for Literature Reviews. In: Lau F, Kuziemsky C, editors. Handbook of eHealth Evaluation: An Evidence-based Approach [Internet]. Victoria (BC): University of Victoria; 2017 Feb 27.
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• Concluding Remarks

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Introduction to primary source research, definitions, examples of primary sources by discipline, head of bancroft public services.

• Archives terminology
• How to use library catalogs
• How to use finding aids/collection guides
• How to plan your visit to an archive
• Using digitized primary sources
• Evaluating primary sources

A primary source is an eyewitness account of an event or data obtained through original statistical or scientific research. 

What are some examples of primary sources?

• Photographs
• Official records (government reports, transcripts, court records, death certificates, etc.)
• Contemporary news reports (newspapers, telecasts, radio addresses, etc.)
• Polls and Public Opinion Data
• Laws, statutes, hearings

Secondary Source

A secondary source interprets and analyzes primary sources. These sources are one or more steps removed from the event. Secondary sources may include pictures of primary sources or quotes from them. Some types of secondary sources include: journal/magazine articles, textbooks, commentaries, and encyclopedias.

Newspapers may be either primary or secondary. Most articles in newspapers are secondary, but reporters may be considered as witnesses to an event.  Any topic on the media coverage of an event or phenomenon would treat newspapers as a primary source. 

Source: https://guides.libraries.indiana.edu/primarysources

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• Last Updated: Apr 8, 2024 3:55 PM
• URL: https://guides.lib.berkeley.edu/primarysourceresearch101

Literature Reviews in Sociology

• Literature Review Process
• Keywords/ Search Terms
• Search Strategies

Literature Review Sources

Beam model for using sources (joseph bizup), using your sources.

• Background & Topic Overviews
• Published Research (Article Databases)
• Grey Literature (Policies & Reports)
• Data & Statistics
• ASA Citation Style
• Research Support

What Types of Literature Should I Use in My Review?

There are several different types of literature available and you may draw on all of them. The ones you will refer to in your literature review generally fall into two main areas.

• Articles in academic journals
• Print books or e-books 
• Government reports, which include policy recommendations
• Private sector research, often marketing research, which is produced for business purposes
• Surveys to provide material for planning enquiries.

Adapted from: Byrne, D. (2017). What types of literature should I use in my review?.  Project Planner . 10.4135/9781526408518.

A source may serve more than one function .  For instance, a journal article could include background information, exhibits, argument and method.  However, some sources are focused on a single function.  For example, an encyclopedia entry on “Alzheimer's disease” is likely to only serve as background information.

Adapted from Bizup, J. (2008) “ BEAM: A Rhetorical Vocabulary for Teaching Research-Based Writing. ”  Rhetoric Review  27.1: 72-86.

Using Your Sources: The BEAM Research Model (3:25), from Portland State University Library

What am I going to do with my sources?  BEAM ask you to consider the function of the source.

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• Published: 05 June 2024

Prevalence of somatic symptoms among Ebola Virus Disease (EVD) survivors in Africa: a systematic review and meta-analysis

• Oscar Onayi Mandizadza 1 ,
• Ropafadzo Tsepang Phebeni 2 &
• Conghua Ji 1  

BMC Public Health volume  24 , Article number:  1511 ( 2024 ) Cite this article

Metrics details

Many Ebola virus disease (EVD) survivors have reported somatic and neuropsychological symptoms after discharge from the Ebola Treatment Unit (ETU). Since the 2014–2016 Ebola epidemic in West Africa, various studies have investigated and identified these symptoms. Evidence on somatic symptoms is widely available in the literature, however, there is no concise overview of the prevalence across different time intervals.

This meta-analysis was conducted following the (PRISMA) guidelines. A database search was conducted to identify original studies that reported the prevalence of symptoms. The primary outcome measure was the prevalence rate of several somatic symptoms. Results were pooled, and prevalence rates were assessed over time, to elucidate any particular trends.

We included 23 studies (5,714 participants). The pooled prevalence was: arthralgia 50% (95% CI: 41%-59%); headache 44% (95% CI: 36%-52%); myalgia 32% (95% CI: 26%-38%); abdominal pain 27% (95% CI: 15%-39%); fatigue 25% (95% CI: 19%-31%); numbness of feet 16% (95% CI: 14%-18%); numbness of hands 12% (95% CI: 10%-14%) and hearing loss 9% (95% CI: 5%-12%). Prevalence across different time intervals revealed significant patterns. All the symptoms persisted for more than 2 years after discharge except for abdominal pain.

The pooled prevalence rates of somatic symptoms are notably high. Arthralgia and headache are the most prevalent of the symptoms, with hearing loss and numbness in hands and feet being the least. We found that arthralgia, myalgia, and abdominal pain decreased over time. However, headache, fatigue, numbness of hands and feet, and hearing loss increased over time.

Peer Review reports

Introduction

Ebola Virus Disease, EVD (formerly known as Ebola Hemorrhagic Fever) is a rare but fatal disease (case fatality rate of 25–90%). It is caused by four ebolavirus strains (Zaire, Sudan, Taï Forest, and Bundibugyo) of the filoviridae family [ 1 ]. The majority of past widespread Ebola virus outbreaks were primarily caused by Zaire (24 outbreaks) and Sudan strains (8 outbreaks). The Zaire strain generally exhibits higher virulence compared to the Sudan strain [ 2 ], therefore accounting for more deaths compared to other strains [ 3 ]. Several African countries have been affected by recurrent outbreaks since its discovery in 1976 (in the Democratic Republic of Congo) [ 4 , 5 ] with more than 30 outbreaks recorded [ 3 , 6 , 7 ]. In order to monitor the post-Ebola health status of survivors, studies have been conducted in previous years. Rowe et al. (1999), recorded one of the earliest findings on symptoms experienced by EVD survivors [ 8 ].

Prior to 2014, there were limited studies on the health challenges faced by EVD survivors due to the small number of survivors. However, the 2014 West Africa outbreak, brought forth a large cohort of survivors. This led to a significant increase in research efforts focused on the well-being of EVD survivors [ 9 , 10 , 11 ]. Notably, many of these studies have been conducted in Africa, where almost all Ebola outbreaks occurred.

EVD survivors report somatic and neuropsychological [ 12 ] symptoms that emerged weeks to years after discharge from the Ebola Treatment Unit (ETU) [ 13 , 14 , 15 ]. Felix Lotsch et al. [ 16 ] reviewed the neuropsychological long-term sequelae in 2017, which is the only existing review on neuropsychological long-term sequelae among EVD survivors. On the other hand, many studies have reported somatic symptoms among EVD survivors. Frequently reported somatic symptoms include headache, fatigue, arthralgia, myalgia, hearing loss, abdominal pain, and numbness of hands and feet. Although these somatic symptoms have been widely reported in literature, there is no concise overview on the prevalence of these symptoms. This study, therefore, aims to determine the prevalence of somatic symptoms among EVD survivors after discharge from an ETU and how these prevalence change over time. This will provide a concise summary of the symptom burden, and its progression over time which will further direct future efforts toward prioritizing care to survivors who by reason of their age are in many instances the breadwinners of the affected societies [ 17 ].

Materials and methods

The study was registered in Prospective Register Of Systematic Reviews (PROSPERO): CRD42023427604.

Search methods for identification

PubMed, Web of Science and Embase were searched by 2 independent authors for articles that reported symptoms experienced by EVD survivors weeks-to-years after discharge from ETU, from the time of database inception to 30 April 2023. References of the included studies were also manually checked to ensure no relevant studies were missed during the search.

Electronic searches

The following key terms were used in the search, “Hemorrhagic fever, Ebola”, “survivor”, “sequelae”, etc. Table S1 (Supplement material) shows the full search string used in each database. No language or age restrictions were applied. The search followed the PRISMA guidelines [ 18 ]. Only studies that quantitatively included the prevalence of the following characteristics were considered: headache, vision problems, fatigue, uveitis, arthralgia, myalgia, hearing loss, abdominal pain, and numbness of hands and feet.

Selection of studies

Studies were selected by 2 independent authors according to the following eligibility criteria:

Original studies: Observational studies (cross-sectional or cohort studies) with primary evidence.

Studies with EVD survivors, confirmed by either an ETU discharge certificate, positive antibody Ebolavirus antibody test (Ig G), or registration in the National Ebola survivor’s databases.

Outcome of interest: Studies that recorded the prevalence of headache, fatigue, uveitis, arthralgia, myalgia, hearing loss, abdominal pain, numbness of hands, and numbness of feet, experienced by EVD survivors weeks-to-years after discharge from ETU.

Exclusion criteria

The study aimed to assess specific post-Ebola symptoms; therefore, studies were excluded if they only recorded symptoms by systems, without specifying the prevalence of the above-mentioned specific symptoms. Case series and case reports were also excluded due to the limited sample size.

Quality assessment

All included studies were observational (Cross-sectional or cohort). The quality was evaluated using the modified Newcastle Ottawa Scale (NOS) for cohort studies and a modified version for cross-sectional studies [ 19 ].

Measures of outcome

The outcomes of interest were the prevalence of the following symptoms: Headache, fatigue, uveitis, arthralgia, myalgia, vision problems, hearing loss, abdominal pain, numbness of hands, and numbness of feet. “Vision problems” was later excluded from the pooled prevalence rate as it was considered non-specific; since different articles referred to different characteristics within the category “vision problems”, limiting generalizability. In addition, uveitis was further excluded, as it depend on specialist assessment rather than self-reported. The pooled prevalence rate was measured for each symptom in Stata version 17. A random-effect model was used to cater for high heterogeneity of the included studies.

Data extraction and management

Data from the included studies were entered into a customized Excel spreadsheet by O.O.M and checked for potential errors by R.T.P. The following characteristics were extracted from each of the included studies: first author, year of publication, year of outbreak, Ebola species, study design, country of study, number of participants, the median age of participants, percentage of males, and meantime (months) from ETU discharge. Moreover, data on the somatic symptoms (headache, fatigue, vision problems, uveitis, arthralgia, myalgia, hearing loss, abdominal pain, numbness of hands, and numbness of feet) were extracted.

Subgroup analysis

Subgroups were evaluated using Stata/MP version 17.0 according to the following categories, to assess the notable trends in prevalence of symptoms across different subgroups. Furthermore, in case of heterogeneity, subgroup analysis was performed to elucidate the potential source of heterogeneity. Subgroups were allocated based on the following characteristics:

Mean Time from ETU discharge: grouped as 6 months, 12 months, 24 months, and more than 24 months.

Study design: Cross-sectional (CS) and Longitudinal cohort studies (LS).

Country of study: Sierra Leone (SL), Uganda (UG), Guinea (GQ), Liberia (LR), the Democratic Republic of Congo (DRC), Sudan and Gabon based on the Center of Disease Control (CDC) list of countries affected by Ebola outbreaks [ 7 ]. No studies from Sudan and Gabon satisfied the inclusion criteria.

Quality of studies: High quality and moderate quality studies.

Meta analysis

We performed a pooled prevalence rate for all the symptoms using the ‘metaprop’ command in Stata 17 [ 20 ]. The ‘metaprop’ command is designed to estimate the pooled prevalence rate, incorporating an in-built double arcsine transformation function. This transformation is essential for stabilization of variance in prevalence studies [ 20 , 21 ]. Furthermore, a meta regression was performed with the following study characteristics as co-variates to elucidate potential contributing factors to high heterogeneity [ 22 ]; Mean time from ETU discharge, study design, country of study, gender (predominantly male: % Male > 50% vs. Predominantly female: % Male < 50%), and the Ebolavirus species.

Assessment of risk of publication bias and sensitivity analysis

Publication bias was evaluated using the Egger’s regression test and also depicted on a funnel plot [ 23 , 24 ]. One-by-one exclusion of studies comparing the I 2 value was performed to identify the source of heterogeneity. I 2 value was used to quantify the statistical heterogeneity [ 25 ]. P  < 0.10 supported the existence of heterogeneity.

Results of the search

A total of 4920 articles were retrieved from the database search. After screening, 23 studies [ 8 , 10 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ] with a total population of 5,714 participants were included. A PRISMA flow diagram was created and is presented for reference [ 37 ] (Fig. 1 ).

PRISMA Flow chart

Characteristics of included studies

An overview of the included studies is shown in Table  1 . The included studies were done in Sierra Leone (11), Liberia (7), and Guinea (3), DRC (1) and Uganda (1). The symptoms experienced by EVD survivors were sparingly distributed across the studies. The prevalence of 10 post-EVD somatic symptoms was recorded weeks to years after discharge from the ETU. Among the 23 included studies, arthralgia (20 studies), headache (16 studies), and myalgia (15 studies) were the three most reported symptoms. Numbness of feet (3 studies) and hands (2 studies) were the least reported. The results of the modified Newcastle Ottawa Score (NOS) evaluation are shown in Table  2 and Table  3 . All included studies were moderate to high quality. (shown in Table  2 and Table  3 ).

The pooled prevalence rate

The pooled prevalence was: arthralgia 50% (95% CI: 41%-59%); headache 44% (95% CI: 36%-52%); myalgia 32% (95% CI: 26%-38%); abdominal pain 27% (95% CI: 15%-39%); fatigue 25% (95% CI: 19%-31%); numbness of feet 16% (95% CI: 14%-18%); numbness of hands 12% (95% CI: 10%-14%) and hearing loss 9% (95% CI: 5%-12%) (Figs. 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 and 10 ).

Prevalence of post-EVD, Numbness of hands

Prevalence of post-EVD, numbness of feet

Prevalence of post-EVD, myalgia

Prevalence of post-EVD, hearing loss

Prevalence of post-EVD, Headache

Prevalence of post-EVD, fatigue

Prevalence of post-EVD, arthralgia

Prevalence of post-EVD, abdominal pain

Period prevalence of post-EVD symptoms

Subgroup analyses were performed for all symptoms to determine any discrepancies across studies, assess the potential source of heterogeneity, and to observe any significant tendencies of these symptoms. Five parameters were assessed: meantime (months) from ETU discharge, study design, quality of study, country of study and presence of control group.

Mean time from ETU discharge.

Results were categorized into four distinct time periods: 0–6 months, 6–12 months, 12–24 months, and more than 24 months post ETU discharge. These intervals excluded the respective lower boundaries (0 months, 6 months, 12 months, and 24 months) to ensure exclusiveness of the time frames (Fig.  10 ). Within the first 6 months after ETU discharge, symptoms such as arthralgia, myalgia, and fatigue, were more prevalent, while headache, abdominal pain, and hearing loss had lower prevalence compared to the overall prevalence. Data on numbness of hands and feet were missing within the first 6 months (Table  4 ). Between 6 to 12 months after ETU discharge, higher prevalence rates were reported for arthralgia, headache, abdominal pain, myalgia, and numbness of feet, while fatigue, and hearing loss reported a lower prevalence. No studies reported the prevalence of numbness of hands in the first year after ETU discharge (Table  5 ). Between 1 to 2 years after ETU discharge, headache, arthralgia, abdominal pain, fatigue, myalgia, numbness of feet, numbness of hands and hearing loss reported a lower prevalence compared to the overall prevalence (Table 6 ). For symptoms assessed more than 2 years after ETU discharge, headache, fatigue and hearing loss were notably high compared to their respective overall prevalence while arthralgia, myalgia, and numbness of feet and hands had a lower prevalence rate. No studies reported the prevalence of abdominal pain more than 2 years after ETU discharge (Table 7 ).

Study design.

Crossectional studies reported a notably high prevalence compared to Longitudinal studies in symptoms such as headache (47% vs. 42%), arthralgia (53% vs. 48%), myalgia (36% vs. 27%), and numbness of feet (18% vs. 15%). Conversely, longitudinal studies reported a notably high prevalence compared to Crossectional studies in symptoms such as fatigue (27% vs. 19%), and abdominal pain (46% vs. 21%)

Country of Study.

In the “country of study” subgroup, studies from 5 different countries satisfied the inclusion criteria. There were notable variations in the pooled prevalence across different countries. Studies performed in Uganda reported the prevalence of 3 symptoms (fatigue, headache, and hearing loss), Liberia reported all the symptoms, Sierra Leone reported all the symptoms except numbness of hands and feet, Democratic Republic of Congo reported 4 symptoms (abdominal pain, arthralgia, fatigue, myalgia) and Guinea reported 6 symptoms (abdominal pain, arthralgia, fatigue, headache, and myalgia). A subgroup of studies conducted in Equatorial Guinea [ 27 , 31 , 32 ] reported the highest prevalence in abdominal pain, arthralgia, and fatigue. The study conducted in Uganda by D.V Clark et al. [ 26 ] reported the highest prevalence in headache and hearing loss. Among the studies conducted in Sierra Leone, the highest prevalence was reported for abdominal pain and myalgia compared to other countries. Detailed prevalence rates are shown in Table 8 .

Quality of study.

Studies were categorized based on their quality as either high or moderate quality. There were significant variation between the two categories. Notably, moderate quality studies reported a higher prevalence in symptoms such as headache (42% vs. 44%), arthralgia (58% vs. 43%), abdominal pain (34% vs. 16%), myalgia (44% vs. 23%), and fatigue (41% vs. 16%) compared to high quality studies. Conversely, high quality studies recorded a higher prevalence in symptoms such as hearing loss (12% vs. 5%), numbness of hands (13% vs. 12%) and feet (17% vs. 14%) compared to moderate quality studies. Numbness of hands and feet were only reported in high quality studies.

Meta regression

We conducted a meta regression with study characteristics such as mean time from ETU discharge, study design, country of study, gender (predominantly male: % Male > 50% vs. Predominantly female: % Male < 50%), and the Ebola virus species, as covariates. The coefficients for all the covariates were almost zero, and the p -values were above the significance threshold of 0.05. The results showed that the covariates were not associated with the prevalence of post-Ebola symptoms (Table  5 ).

Results of publication bias assessment and sensitivity analysis

We evaluated the impact of publication bias on our findings using the Egger’s regression test and depicted the results using a funnel plot. There was significant publication bias (Egger’s test, p  = 0.027). The funnel plot is shown in Fig. 11 . We performed a sensitive analysis test (omitting studies at a time), to elucidate the effect of individual study on the overall prevalence. Studies by A.K Rowe et al. [ 5 ], D.V Clark et al. [ 26 ] and R.E.G Wadoum et al. [ 34 ], notably influenced the overall pooled prevalence. This impact could be attributed to shorter mean time (2 weeks) from ETU discharge [ 34 ], different ebolavirus strain [ 26 ] and different employed methodology.

Funnel Plots of post EVD symptoms

Several studies have reported a notably high prevalence of somatic symptoms among EVD survivors several weeks to year after discharge from an ETU. The impact of somatic symptoms on EVD survivors’ ability to resume to their normal work has been a major concern [ 38 , 39 , 40 ]. Therefore, we thought it expedient to estimate the overall prevalence of somatic symptoms experienced by EVD survivors across different time intervals following discharge from the ETU. To our knowledge, this is the only existing systematic review and meta-analysis on post EVD somatic symptoms. 23 studies were included, with a cumulative total of 5,714 EVD survivors (over 30% of all EVD survivors) [ 41 , 42 ].

Our study showed high prevalence rates of post EVD symptoms (9%-50%). Arthralgia (50%), headache (44%), and myalgia (32%) had the highest prevalence, supporting existing evidence [ 28 , 35 , 40 , 43 , 44 ]. Generally, most of the somatic symptoms were relatively more prevalent (except for numbness of hands and feet, and hearing loss) within the first year. Numbness of hands and feet were more prevalent more than one year following discharge from ETU. The prevalence of arthralgia and myalgia regressed between 12–24 months. However, headache, fatigue, hearing loss, numbness of hands and feet gradually increased over time. Evidence on prevalence of post EVD symptoms more than 24 months after discharge, remains inconclusive due to limited studies [ 26 , 39 , 45 ], there is need for more research to evaluate the fate of these symptoms. The decline of symptoms over time can be significantly influenced by whether or not EVD survivors received prior treatment, therefore studies performed in clinics were more likely to reflect a significant decrease over time [ 34 , 40 ]. This observation also highlights the importance of early treatment in mitigating symptom burden among EVD survivors. Moreover, a study conducted by D.V. Clark et al. reported a notably high prevalence of most somatic symptoms. It is worth noting that this study specifically examined post-Ebola Virus Disease (EVD) symptoms among EVD survivors of the Bundibugyo strain, rather than the Zaire ebolavirus, making it the only included study with this particular focus. Therefore, variation in prevalence possibly exist across different Ebola strains [ 38 ]. H. Mohammed et al., explored the link between febrile presentation and post EVD symptoms, presuming that febrile presentation could be indicative of another active infection (by other pathogens). Interestingly, the febrile group showed a significantly higher prevalence of headache and fatigue (weakness) compared to the non-febrile group. Therefore, there could be potential inference to comparison of post-infectious symptoms with post-EVD symptoms [ 46 ]. It is therefore essential to consider the inclusion of a control group consisting of individuals with no known exposure to Ebola for improved comparability in future research studies. The prevalence remained significantly high across different subgroups (study design, country of study and study quality). The variations in prevalence across different countries could be attributed to many factors such as number of participants enrolled, healthcare systems and accessibility of health services, socioeconomic status of affected population, different ebolavirus strains [ 26 ], cultural beliefs among many other. Heterogeneity was potentially due to variations in age, sex, study population, and use of different methodology across studies.

Several mechanisms have been proposed as potential causes of post Ebola symptoms. First, ebolavirus can accumulate in immune-privileged areas such as the testis, central nervous system (CNS), and ocular fluids leading to inflammation (due to reactivation) and direct tissue damage [ 47 ]. Viral persistence in ocular fluid and CNS can cause eye and neurological damage [ 48 ], leading to neurological [ 49 ] and ocular symptoms. Second, ebolavirus causes a robust immunological reaction during acute infection. This leads to an excessive secretion of cytokines, such as tumour necrosis factor (TNF-α), interleukin 6 and interferons which can alter the immunological function [ 50 ]. Third, N. G. Bond et al. [ 45 ], also described overlapping symptom clusters among EVD survivors, proposing a common underlying mechanism. More evidence is required. Fourth, the healthcare systems, accessibility of health services, socioeconomic status, and prior health status of affected population, could be contributing to the persistence of post Ebola symptoms. EVD survivors in other affluent societies (United States of America) reported complete recovery within a short time [ 51 , 52 ]. Poor prior health status could impact the duration of the recovery stage.

Scarcity of data on the post-somatic symptoms in EVD survivors has made it difficult to comprehensively understand the underlying mechanisms behind these persistent symptoms. However, the global impact of the COVID-19 pandemic has provided more data for research on post-viral sequelae. Researchers have extensively documented the long term post-COVID-19 symptoms including fatigue and neurological impairments, which are quite similar to the complaints in EVD survivors. The extensive data available on COVID-19 could provide some insights into potential mechanisms and management strategies for both groups of survivors [ 53 ].

Our study had several limitations. First, only few studies mentioned the participants’ prior medical history [ 30 , 54 , 55 ]. It is suspected that self-treatment methods might have been used [ 56 ], however, none of the studies reported whether or not there was prior treatment by over the counter (OTC) drugs (or other means). Prior treatment can influence the duration of the symptoms. Second, although most studies reported the male-to-female proportions, only one study separated the symptoms experienced by men from those experienced by female participants. Furthermore, variation existed in included age groups among the included studies. Majority encompassing both pediatric and adult participants. These studies reported their results collectively, without differentiating between age groups. Hence, we were unable to assess for heterogeneity across studies based on age, and sex, which are major potential sources of heterogeneity. Future studies should improve on this. Third, some studies were conducted at designated clinics that provided free treatment services which may have led to a potential overestimation of the prevalence rates, as the availability of free services could attract a larger number [ 30 , 33 , 57 ]. Fourth, individual perception of health can vary and might influence whether or not a particular symptom is reported. Therefore, the prevalence rates reported across studies might have been impacted (over or under-estimated) by individual reporting biases. Fifth, Ebola outbreaks occurred in low-resource communities, which previously had limited access to health-care facilities. Therefore, the observed post-Ebola health outcomes could have been influenced by prior health status of the community. Despite the aforementioned limitations, our findings contribute valuable evidence that can serve as a foundation for further research to elucidate the precise mechanisms underlying post-Ebola symptoms. Regions affected by recurrent Ebola outbreaks often rely on agriculture, mining, and trade as their primary means of livelihood [ 17 ]. Moreover, it is evident that the majority of these symptoms have a significant impact on individuals' daily activities and overall quality of life. Since most EVD survivors are within the working-age population, they serve in many instances as the breadwinners of the affected societies. Relatively due to stigma [ 58 ] and persistent somatic symptoms, some EVD survivors were unable to resume work [ 59 ]. Therefore, there is a need to provide timely intervention to this population.

A large cohort of EVD survivors complain of somatic symptoms weeks to years after discharge from ETU. The pooled prevalence rates of somatic symptoms are notably high. Arthralgia and headache are the most prevalent of the symptoms, with hearing loss and numbness in hands and feet being the least. We found that arthralgia, myalgia, headache, and abdominal pain decreased over time. However, headache, fatigue, numbness of hands and feet, and hearing loss increased over time.Unlike previous studies, we had a large cumulative total of 5,714 participants. In addition, we uniquely documented the trends in prevalence rates in different time intervals. The prevalence rate of post EVD somatic symptoms is notably high, highlighting the need for optimizing care up to two years after discharge from ETU.

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Acknowledgements

We thank all the participants and clinical researchers involved in the publications cited in this study. All authors listed meet the authorship criteria according to the latest guidelines of the International Committee of Medical Journal Editors, and that all authors are in agreement with the manuscript.

This study was supported by the Department of Science and Technology of Zhejiang Province (No. 2023C25012).

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This research was conducted by O.O.M and R.T.P under the supervision of professor C.J.H. The manuscript was compiled by the three authors.

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Mandizadza, O.O., Phebeni, R.T. & Ji, C. Prevalence of somatic symptoms among Ebola Virus Disease (EVD) survivors in Africa: a systematic review and meta-analysis. BMC Public Health 24 , 1511 (2024). https://doi.org/10.1186/s12889-024-19013-8

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Received : 12 July 2023

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DOI : https://doi.org/10.1186/s12889-024-19013-8

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