Systematic Reviews and Evidence Synthesis

Grey literature is an umbrella term for research literature that is not published through traditional means and often excluded from traditional academic databases. Grey literature is often produced by government agencies, corporate industries, academics, or nonprofit organizations. Grey literature is usually not controlled by commercial publishers, and is typically not peer reviewed.

In short, grey literature refers to the wide range of research literature that falls outside of the traditional, peer-reviewed, academic journal article.

Grey literature can be incredibly valuable for systematic and scoping reviews As grey literature falls outside the traditional norms of publishing, it has unique value. As the goal of systematic and scoping reviews is to fully map the available evidence, it can be critical to include grey literature to ensure you are using the best available evidence. Additionally, the inclusion of grey literature is recommended by existing review standards, is increasingly expected by journal editors, and is becoming increasingly common in evidence synthesis projects.

 The benefits of using grey literature include:

• Finding information not found in traditional sources
• Countering publication biases found in academic journals
• Including more diverse perspectives in your research
• Creating a more comprehensive view of the research literature
• Including the most recent research and avoiding the time gap between research and publishing

Grey literature spans a wide range of document types, including:

• Preprints
• Reports and white papers
• Conference proceedings
• Dissertations and theses
• Clinical trial registrations
• Policy documents
• Government publications

Grey literature can be hard to find, but there are some go-to resources you can consider when searching for grey literature. We highly recommend asking a librarian for help finding grey literature. You can find grey literature in:

• Academic databases - some academic databases, such as Scopus and CINAHL, include types of grey literature like conference proceedings and dissertations
• Preprint servers - There are dedicated preprint websites for many disciplines, as well as multidisciplinary preprint servers. Ask a librarian for help identifying the most relevant preprint server(s) for your project. For example, MedRxiv is the go-to preprint server for health sciences research.
• Clinical trial registries - Clinical trial registries such as ClinicalTrials.gov are great sources of research that is still in its early phases or has just recently completed
• Dissertation/theses databases - Dedicated dissertation/thesis databases can help you identify work that doesn't always end up in academic journals
• Government information - Searching or browsing the websites of government agencies relevant to your research topic can be a great way to find reports, white papers, and statistics
• Nonprofits and organizations - There are many nonprofits, think tanks, and independent research organizations that produce high-quality reports and white papers