Systematic Reviews & Other Evidence Synthesis

What Is Grey Literature?

Grey literature is information produced by individuals or organizations outside of traditional academic publishing channels. This includes:

• dissertations and theses
• reports, white papers, and other documents from government agencies, NGOs, or other organizations
• conference proceedings
• unpublished or self-published research
• and more

The grey literature sources you select will be informed by your research question and field of study, but often likely include, at a minimum, dissertations and theses.

Some grey literature is included in databases (e.g., many dissertations and theses, as well as conference proceedings), and some will be harder to find. A librarian can help you determine where you might look for this material.

Why Include Grey Literature?

The intent of an evidence synthesis is to synthesize all available evidence that is applicable to your research question. There is a strong bias in academic publishing toward publishing studies that show some sort of significant result or effect. Meanwhile, many studies and trials that show no result or effect end up going unpublished. Meanwhile, early-career researchers and researchers from marginalized groups or the Global South may not have adequate access to traditional academic publishing outlets. While not peer reviewed, grey literature represents a valuable body of information that is critical to consider when synthesizing and evaluating all available evidence.

How Do I Manage a Grey Literature Search?

Taking the following steps will help you systematically search for grey literature:

• Identify and record the sources you will search. The sources you search will be informed by your research question and where you expect to find information related to your question.
• Document where you are searching and your search strategies, including document resource names, URLs, search terms, and dates searched.
• Collect and organize citation information as you go, such as by utilizing a citation manager (e.g., Zotero, EndNote).
• Adhere to your established inclusion and exclusion criteria when selecting grey literature sources.

Searching systematically for grey literature can be challenging. But here are a few approaches you can take to add some structure to your search for this type of information:

• Search for dissertations and theses. (See below for possible sources.)
• Search in databases that specialize in grey literature. 
• Refer to the grey literature sources used for evidence syntheses and noted in registered protocols on similar topics.
• Ask experts in the field for recommendations for relevant grey literature sources. If you are an expert, ask colleagues for their recommendations.
• Contact known researchers in the field to determine if there are any ongoing or unpublished studies that they may be aware of.
• Identify government agencies and international and non-governmental organizations that might publish technical papers and reports on your topic. Search their websites or any online libraries that they provide.
• Search for relevant conference proceedings. Identify professional organizations that offer conferences at which researchers might be presenting work related to your topic. We recommend that you search proceedings for the three most relevant conferences for your evidence synthesis.
• Search for relevant trade publications (e.g., newsletters or magazines published by organizations in the field).