Grey literature is defined as material created by government agencies, academics, business and industry in print and electronic formats, but which is not published by commercial publishers and is not indexed in bibliographic databases. Examples include government-issued papers, research reports, technical papers, dissertations, briefing documents, and conference presentations.
The key bodies producing evidence summaries, systematic reviews and meta-analyses – Cochrane Collaboration, Campbell Collaboration and the Joanna Briggs Institute – recommend that reviewers include a search for relevant grey trials and unpublished reports. By searching grey literature sources, reviewers improve the quality of the search and reduce the possibility of publication bias.
For any research query, we suggest searching in this sequence:
The following grey literature sources are freely available to search.
Trials are frequently reported in conference papers, even if many do not progress to full publication.
The AACODS checklist, developed by Jess Tyndall in 2010, suggests six criteria.
Tyndall, Jess, Health librarians and grey literature: what do we need to know? Invited lecture presentation and notes. Presented Royal Melbourne Hospital, July 15 2014 and Royal Adelaide Hospital, September 25 2014. Retrieved from
Canadian Agency for Drugs and Technologies in Health. Grey matters: a practical search tool for evidence-based medicine.
Staff at CADTH developed the Grey Matters checklist to help searchers in
a) ensuring retrieval of relevant grey literature items
b) documenting the process for searching grey literature sources (to increase transparency of the search methods)
c) standardising the search process.
The checklist presents a large array of websites, allowing searchers to methodically record the keywords used and results obtained from each resource.