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What is grey literature
“There are many definitions of grey literature, but it is usually taken to mean literature that is not formally published in sources such as books or journal articles.” Cochrane Handbook- 188.8.131.52 Grey literature databases.
- Registered Controlled Trial Registers
- Technical or research reports from government agencies
- Reports from scientific research groups
- Working papers from research groups or committees
- Doctoral (PhD) dissertations
- Some conference proceedings and official publications
- Preprints (journal articles not yet peer-reviewed and/or published)
Why search the Grey Literature?
The intent of a systematic review is to synthesize all available evidence that is applicable to your research question. There is a strong bias in scientific publishing toward publishing studies that show some sort of significant effect. Meanwhile, many studies and trials that show no effect end up going unpublished. But knowing that an intervention had no effect is just as important as knowing that it did have an effect when it comes to making decisions for practice and policy-making. While not peer-reviewed, grey literature represents a valuable body of information that is critical to consider when synthesizing and evaluating all available evidence.
Controlled trial registers
Trial Registers are a useful source of unpublished and ongoing trials:
PhD Theses and Dissertations
Preprint is a term that tends to mean a version of a manuscript that is self-archived and shared publicly before publication in a scholarly journal - often the version prior to peer review. You may wish to include searches for preprints in your systematic review.
There are a number of different sources for finding preprints. For example:
- MedRxiv: launched in June 2019, this health sciences preprint server is a collaborative effort between Cold Spring Harbor Laboratory, BMJ and Yale. Submissions are screened to deter potential risk to public health.
- bioRxiv: launched in 2013, this repository contains research from the life sciences and is maintained by Cold Spring Harbor Laboratory. bioRxiv facilitates direct transfer of submissions to participating journals.
- OSF preprints: several partner repositories are hosted on the Open Science Framework (OSF) preprint platform. The partner repositories vary by discipline, region and screening process.
- See a comprehensive list of preprint servers at: http://z.umn.edu/PreprintRepositories
- See also this paper for useful information on finding preprints: Langham-Putrow, A., & Riegelman, A. (2019). Discovery and scholarly communication aspects of preprints: Sources for online information. College & Research Libraries News, 80(9), 506-510. https://doi.org/10.5860/crln.80.9.506
Reporting grey literature searching
When you are writing up your review remember to report on any grey literature searching you have done.
Describe any online or print source purposefully searched or browsed (e.g., tables of contents, print conference proceedings, web sites) and how this was done.
- “We also searched the grey literature using the search string: "public attitudes" AND "sharing" AND "health data" on Google (in June 2017). The first 20 results were selected and screened.”
- “The grey literature search was conducted in October 2015 and included targeted, iterative hand searching of 22 government and/or research organization websites that were suggested during the expert consultation and are listed in S1 Protocol. Twenty two additional citations were added to the review from the grey literature search.”
- “To locate unpublished studies, we searched Embase [via Embase.com] for conference proceedings since 2000 and hand-searched meeting abstracts of the Canadian Conference on Physician Health and the International Conference on Physician Health (2012 to 2016).”
Read more: PRISMA-S: An Extension to the PRISMA Statement for Reporting Literature Searches in Systematic Reviews https://doi.org/10.31219/osf.io/sfc38
Grey Literature Resources
OpenGrey European database of grey literature
Database of 700,000 bibliographical references of grey literature (paper) produced in Europe. Includes technical or research reports, doctoral dissertations, conference papers, official publications. Covers: Science, Technology, Biomedical Science, Economics, Social Science and Humanities. You can use the Zotero Chrome extension to export results page-by-page.
IRIS (World Health Organisation)
IRIS (Institutional Repository for Information Sharing) is the digital library of the WHO's published material in full text produced since 1948. Covers: WHO governing bodies, publications, technical documents, guidelines and journal articles. Searches can be based on individual Communities & Collections
which are primarily based around large geographical areas. Content is free.
Global Index Medicus (World Health Organisation)
Complements and provides an extended perspective to databases such as PubMed. It is produced by and within low- and middle- income countries. The WHO regional offices make biomedical and public health literature available via: African Index Medicus; LILACS (South and Central America, and the Caribbean); Index Medicus for the Eastern Mediterranean Region; Index Medicus for South East Asia Region; Western Pacific Region Index Medicus. In addition to the value of revealing this content to a wider audience, it can also be important for the creation of systematic reviews.