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Systematic Reviews: Grey Literature & Handsearching

A guide to conducting systematic reviews.

What is Grey Literature

Grey literature refers to both published and unpublished research material that is not available commercially.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
  • Newsletters
  • Pamphlets
  • Reports
  • Social media: Twitter, Facebook, LinkedIn, etc.
  • 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  • Including unpublished results reduces publication bias, which includes the phenomenon that studies reporting a positive result are more likely to be published than those finding a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  • Incorporating unpublished trial data can change statistical results.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.

Where to Find Grey Literature

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Learn More about Grey Literature


IOM Standard 3.2.4 states: that researcher should "Handsearch selected journals and conference abstracts." Handsearching can be done of either paper or electronic journals and involves a page-by-page search. Reasons for handsearching include:

  • Indexing inconsistencies
  • Selective inclusion of articles
  • Difficulty of retrieving non-English articles in a database search