Grey literature refers to information sources that are beyond the reach of traditional bibliographic databases. Examples of grey literature include theses and dissertations, conference proceedings, government reports, data and statistics, newsletters, technical reports, standards & clinical guidelines, recommendations, presentations and lecture notes. As grey literature comes from varied sources, it can be typically hard to find.
Grey literature is described as ‘highly desirable’ in the evidence landscape (The Cochrane Collaboration, 2022, see 4.3.5). Grey literature provides a broader perspective on research topics than that provided with only an academic focus. Therefore, it helps reduce publication bias (Paez, 2017) in reviews.
Further reading:
Paez A. (2017). Gray literature: An important resource in systematic reviews. Journal of evidence-based medicine, 10(3), 233–240. https://doi.org/10.1111/jebm.12266
Mahood, Q., Van Eerd, D., & Irvin, E. (2014). Searching for grey literature for systematic reviews: challenges and benefits. Research synthesis methods, 5(3), 221–234. https://doi.org/10.1002/jrsm.1106
If you are looking for academic papers and advice on how to search in electronic databases, check out our Literature Searching Guide.
Google is a popular place to start looking for grey literature. Use these tips below to search more effectively in Google.
| Search operators & description | Examples |
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AND Words are linked with AND by default so you don't need to use AND between your keywords. |
The below search terms will bring back similar results: clinical AND governance clinical governance |
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OR Using OR would broaden your search to find results that include at least one of the keywords. Remember to use OR in capitals. |
governance OR framework OR model lumbar puncture OR spinal tap |
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- Use the minus sign to exclude certain words in your search. Similar to the Boolean NOT operator. |
smoking -vaping transition to practice -nursing |
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" " Use quotation marks for exact phrase searching. |
"mental health awareness" "addiction to nicotine" |
Further information on designing search strategies and documenting and reporting the grey literature search can be found here (Severn M, Mierzwinski-Urban M, Farrah K, Walter M, Spry C, Argáez C, 2023).
As an international partner with WHO, Alliances products annual reports on health policy and system research.
APO is an online knowledge hub that makes public policy research visible, discoverable and usable. The database contains over 38,000 resources, including specialist collections, grey literature reports, articles and data to help you create informed policy and keep you updated with the latest policy and practice research and resources.
For research and learning in agriculture, the environment and the applied life sciences.
A free online tool for finding health-related grey literature that are not published commercially, and which may be inaccessible via bibliographic databases.
Grey literature related to palliative care.
A collection of open dissertations managed by EBSCO.
A search engine for datasets and statistics via the Google platform.
A portal for searching information on grey literature in Europe.
Australian Institute of Health and Welfare, Australian Government.
Australian Commission on Safety and Quality in Health Care - Search their Resource Library
Australian Commission on Safety and Quality in Health Care
Australian Bureau of Statistics
Funded by Health Education England.
OATD.org - aims to be the best possible resource for finding open access graduate theses and dissertations published around the world - over 1,100 colleges, universities, and research institutions.
National Institute for Health Research (NIHR) - an International prospective register of systematic reviews, including unpublished systematic reviews.
A portal to search for U.S. government science information, including technical reports and other grey literature
Trip is a clinical search engine designed to allow users to quickly and easily find and use high-quality research evidence to support their practice and/or care. Create a Trip Pro account to create alerts, save searches, and for CME purposes.
Centers for Disease Control and Prevention (CDC)
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