Grey literature refers to both published and unpublished research material that is not available commercially. In general, grey literature publications are non-conventional and sometimes ephemeral publications that are not indexed in databases such as PubMed and Embase.
Grey literature includes:
- Clinical trials
- Dissertations and theses
- Conference proceedings
- Government reports and documents
- Maps
- Newsletters
- Pamphlets
- Reports
- Social media: Twitter, Facebook, LinkedIn, etc.
- Statistics and data
- Technical specifications and standards
- Technical and commercial documentation
Why search grey literature:
- Including unpublished results reduces publication bias, which includes the phenomenon that studies reporting a positive result are more likely to be published than those finding a negative result.
- Incorporating unpublished trial data can change statistical results.
- Global literature should be included.
- Grey literature is often more current.
- Current IOM systematic review standards call for grey literature inclusion.
Searching the Grey Literature by 
