The Cochrane Handbook for Systematic Reviews of Interventions defines grey literature as "the kind of material that is not published in easily accessible journals or databases".
Search grey literature sources that make the most sense for your research question. These sources can include: materials and research produced by organizations outside of the traditional commercial or academic publishing, conference proceedings, dissertations, published reports or datasets and government documents.
The following sources are recommendations. If you are searching only for grey literature in databases, consider limiting your search by "publication type". Grey Literature can include technical reports, annual reports or government publications, etc.
|General Grey Literature Sources||Databases for Grey Literature|
|Google Scholar||Cochrane Library|
|World Health Organization||PsycINFO|
|Agency for Healthcare Research and Quality||Web of Science|