Knowledge Synthesis: Systematic & Scoping Reviews

What is Grey Literature? Alternative spelling: Gray Literature

also known as fugitive or invisible literature because of its elusive nature. 

Grey literature, according to the Cochrane Handbook, is usually understood to be literature not formally published in books or journals. This can include theses or dissertations, conference proceedings, clinical trials registries, white papers, government reports, and more. Some grey literature will be retrievable through database searching, but it depends on the databases you have chosen to search and what kind of content the databases index. For example, MEDLINE does not index much grey literature, whereas you can retrieve some conference proceedings indexed in Web of Science Core Collection databases 

You may be interested in finding grey literature available on websites. One suggestion is to identify associations, organisations, institutions, etc. that are likely to make documents or reports of relevance to your question available on their websites, and to then selectively search or browse those sites.

Types of Grey Literature

• Blog posts & Tweets
• Census data (research guide)
• Clinical Trials
• Conference Abstracts & Proceedings
• Dissertations/Theses
• Meetings
• Registered Research
• Technical Reports & Systematic Reviews
• Government agencies and reports
• Policy Literature
• Academic institutions
• Annual Reports
• Powerpoint slide presentations
• Webinars

• Newspapers

Why is Grey Literature Useful?

Grey Literature can supplement the formal books and articles you use for your research. Grey literature may be more current than published works or offer different perspectives that you want to consider and cite.

For systematic and scoping reviews, a grey literature search may be mandatory or strongly recommended. For instance, Cochrane's MECIR standards recommend authors: "Search relevant grey literature sources such as reports, dissertations, theses, databases and databases of conference abstracts. Searches for studies should be as extensive as possible in order to reduce the risk of publication bias and to identify as much relevant evidence as possible."

Published journals may be susceptible to biases against reporting negative or neutral outcomes, a phenomenon known as "positive result bias." Researching grey literature or cross-referencing published studies with their grey literature counterparts (e.g. study protocols, clinical trials) can help combat various publication biases.

When to Use Grey Literature?

If Grey Literature on your topic will provide:

• More current, better coverage of emergent research areas
• More widely accessible by you and your potential audience
• A source of more diverse perspectives than mainstream publications offer
• More detailed than journal articles, with raw data or more extensive context
• A better source of information on policies and programs

Grey Literature Checklists

• Public Health Grey Literature Sources (Ontario Public Health Libraries Association)SRC Grey Literature Tips and Checklist
• CADTH Grey Matters Search Tool

  CADTH's Grey Matters resource is a free online tool for finding health-related grey literature that are not published commercially and which may be inaccessible via bibliographic databases.

• CADTH Grey Matters Tool [Word version]

  Tracking tool for many common grey literature sources in health

Grey Literature Searching & Documentation Templates

• How to find and document grey literature - Fillable form for planning out your grey literature search strategy, and documenting it for writing your review. 

Key Resources for Grey Literature

• Canadian Health Research Collection - This is a collection of monograph publications from Canadian research institutes, government agencies and university centres working in the area of health and medical research. The organizations included in this collection are very active publishers of primary research in the field. The publications included are both general policy documents as well as those of a specialized technical nature. There are over 5,000 titles in the current collection, and the service provides more than 1600 additional current documents to subscribers each year.
• NAHRS Finding Grey Literature - Resources suggested by Nursing and Allied Health Resources Section (NAHRS) members for finding Grey Literature.
• Canadian Public Policy Collection - Collection of monograph publications from Canadian public policy institutes, government agencies, advocacy groups, think-tanks, university research centres and other public interest groups representing the leading edge of primary research and opinion in all areas of Canadian public policy.
• ProQuest Dissertations & Theses Global - Database contains more than 2 million entries for doctoral dissertations and master's theses.
• Ontario Health Libraries Association - A selection of evidence-informed resources, and custom search engines for public health practice in Ontario.

More Resources:

• Videos & How-Tos
• Grey Matters: A Practical Search Tool for Evidence-Based Medicine, 2019, Canadian Agency for Drugs and Technologies in Health (CADTH)
• Grey Literature Tutorial courtesy of University of Toronto - This list provides only a few producers and collectors of grey literature. Do a thorough search for sources in your field.
• GreyNet - Includes an international directory, a journal, and an index of relevant websites.
• OpenGrey - A large database of European grey literature
• Health Canada
• CADTH - Canadian Agency for Drugs and Technologies in Health - Includes resources such as rapid response reviews, guidelines, and health technology assessments.
• CIHI - Canadian Institute for Health Information - A non-profit organization that provides information on the state of Canada's health care system and the overall health of Canadians. Includes performance indicators, statistics, standards, reports, and more. Information is included on primary health care, hospital care, community care, and specialized services.
• OAIster - A catalogue with millions of records from open access sources.
• NCCPH (National Collaborating Centres for Public Health) - Links to the six NCCPHs which translate existing knowledge to produce and exchange relevant, accessible, and evidence-informed products with researchers, practitioners, and policymakers (Aboriginal Health, Determinants of Health, Environmental Health, Infectious Diseases, Healthy Public Policy, Methods and Tools). Includes presentations, evidence reviews, reports, summaries, etc.
• Ontario Population Health Index of Databases (OPHID) - OPHID is a free database index resource for researchers, students, or anyone working on or with population health issues. It provides an on-line, searchable index of a wide variety of Ontario (as well as Canada) data sources (there are 600+ to date), details about content, and how to gain access to them.
• Social Sciences Research Network - A platform for the dissemination of early-stage research. From its initial focus on the social sciences in 1994, SSRN has grown to become the most interdisciplinary service of its kind, representing disciplines across the full research spectrum, including the applied sciences, health sciences, humanities, life sciences, physical sciences, and social sciences. 
• Canadian Electronic Library - This collection focuses on Canadian public policy and contains publications from government and non-government organizations. It is a multidisciplinary collection of electronic books from Canadian publishers. Dates of publications vary by publisher - for more recent publications from Canadian publishers, please search Omni.
• Global Health Observatory (GHO) Data - WHO's gateway to health-related data and statistics for its 194 Member States. GHO theme pages cover global health priorities such as the health-related Millennium Development Goals, mortality and burden of disease, health systems, environmental health, noncommunicable diseases, infectious diseases, health equity and violence and injuries. The theme pages present:  highlights showing the global situation and trends, using regularly updated core indicators; data views customized for each theme, including country profiles and a map gallery; and publications relevant to the theme.
• The Grey Literature Report - The report was a publication produced by the The New York Academy of Medicine between 1999-2016, alerting readers to new grey literature publications in health services research and selected urban health topics. The website and database was discontinued in 2017 and is no longer updated, but the resources will still be accessible.

Search tips for Google, Google Scholar, DuckDuckGo, and other search engines 

 When searching for your topic try including a site limit to target the literature produced by a type of organization, group, or government, etc.

For example here are 5 ways to limit:

• site:.net  
• site:.edu
• site:gc.ca
• site:.wordpress.com

Basic Google Operators 

The more search terms you enter, the more focused and specific your results will be. You do not have to use AND to connect your search terms. So each of these searches will get more and more focused:

• Food insecurity homelessness 
• Food insecurity Sleeping Rough
• Food Insecurity Sleeping Rough Ethics

Phrase searching

You can put quotation marks around a phrase to force a search engine to find those exact words, in that exact order:

“Food Insecurity” "Sleeping Rough" Homelessness 

Since there is no truncation (*) in most search engines, to give the search engine alternative forms to search for, use OR (all caps) and parentheses:

(Encampment* OR unhoused OR homeless) (ethics OR moral OR rights)

Use AROUND (all caps) and specific numbers in parentheses to find words or phrases within a certain number of words of each other on a web page:

“Food insecurity” AROUND(3) Homelessness

Advanced Google Operators                  

Google Scholar Tips

For an excellent resource on searching with Google see the Google Advanced Power Searching page.

• Effective Google Scholar search tips

Remember:  Evaluate and Report What You Find

Reporting your grey literature search is not as straightforward as reporting a search on a bibliographic database. You should aim to record the following information:

• Name of web-site or resource used
• URL (if appropriate)
• Date of search
• Keywords  used for searching or details of how you browse

• Evaluate what you find - Because grey literature does not go through the same peer review process of something published commercially, caution needs to be taken when selecting grey literature to use.  As with any resource, even formally published ones, bias or inaccuracies can exist and it is important to have some understanding of the author/originator of the information and their stance on a particular topic or issue.
• Issues around longevity - Resources openly available on the Internet can sometimes vanish, particularly if they are older items or if the website is not being kept up.  If you find something useful, grab it!  Typically things found in a repository or database have more longevity, but for one-off items posted on a website, that is not always the case.