What is grey literature?
Grey literature is the term used to describe literature that is not formally published as a book or journal article (Higgins, 2011), including:
Related library guides:
Grey literature resources:
Some library databases contain grey literature in addition to journal articles. For example, PsycINFO includes dissertations; Embase and Medline/PubMed include conference proceedings. Library databases like Medline/Pubmed, however, do not provide comprehensive coverage of grey literature so other resources should be searched to identify literature that is not formally published.
Clinical trials registries:
For quantitative systematic reviews of healthcare interventions, it is strongly recommended to search clinical trial registries for on-going and unpublished trials in order to limit publication bias. Refer to Section 6.2.3 Unpublished and Ongoing Studies in the Cochrane Handbook for Systematic Reviews of Interventions for more information.