Finding Grey Literature: Grey Literature in Systematic Reviews

The Importance of Grey Literature in Systematic Reviews

Systematic reviews often require a comprehensive search of grey literature, with clear documentation of the strategies used. This is essential for gaining a complete understanding of the literature available on a subject and for avoiding null result publication bias, which can skew analysis if only published studies are considered. Both Cochrane and JBI, leading authorities in health science reviews, strongly recommend searching grey literature to ensure a thorough and unbiased review.

Comprehensive Search Techniques

Since systematic reviews require comprehensive search techniques, it may be necessary to use several or all the search techniques discussed on the searching page: searching grey literature databases, using a search engine, looking for information from organizations, and reviewing previous systematic reviews and consulting colleagues. When using search engines, JBI recommends that you review the first 5-10 pages of results (2020, Section 5.2.4.3).

Documenting Searches for PRISMA

It is also important to document all your searches for a systematic review so they can be repeated if necessary. For grey literature searching, you may consider recording the search strategies used, the number of results captured, and the number selected for screening. This information should be included in your PRISMA flow diagram and methods section in your paper.  Learn more about documenting grey literature searches on our guide to Creating a PRISMA Flow Diagram.

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