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A Guide to Evidence Synthesis

The Grey Literature Background

What is Gray Literature? 


Gray (or grey) literature is literature produced by individuals or organizations outside of commercial and/or academic publishers. This can include information such as government reports, conference proceedings, graduate dissertations, unpublished clinical trials, and much more.  The sources you select will be informed by your research question and field of study, but should likely include, at a minimum, theses and dissertations.

Why Search the Grey Literature

Why Search the Gray 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 scientific publishing toward publishing studies that show some sort of significant effect.  Meanwhile, many studies and trials that show no effect end up going unpublished.  But knowing that an intervention had no effect is just as important as knowing that it did have an effect when it comes to making decisions for practice and policy-making. While not peer-reviewed, gray literature represents a valuable body of information that is critical to consider when synthesizing and evaluating all available evidence.

How to Search the Grey Literature

How Do I Search the Gray Literature?  


Finding gray literature and searching it systematically is challenging.  But there are a few approaches that you can take to add some structure to your search of this type of information:

  • Search databases that specialize in gray literature:  See the box below for more information.
  • Search for theses and dissertations:  There are a number of databases dedicated to theses and dissertations, which you can search using your search terms.  See the box below for links to these resources. 
  • Search clinical trials: There may be clinical trials being conducted that are relevant to your research question, but that haven't been published yet or never were published. See the box below for links to these resources. 
  • 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 may provide.  See the box below for links to some examples.
  • Search conference proceedings and newsletters:  Identify professional organizations that have and/or conferences at which researchers might be presenting work related to your topic.  Search those conference proceedings or newsletters on the organization's website or by contacting organizational boards for access to past proceedings that may not be online. See the box below for some examples.
  • Contact known researchers in the field to determine if there are any ongoing or unpublished studies that s/he may be aware of.
  • Search professional and trade magazines. Professional magazines contain literature that is written by professionals in the field for other professionals in the field, but that may not be about research. Trade magazines contain advertisements and news very specific to a topic or industry.

How to Manage the Grey Literature Search

How Do I Manage the Gray Literature Search?


  • 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 name, URL, search terms, and date searched.
  • Collect citation information as you go.
  • Adhere to your established inclusion and exclusion criteria when selecting sources.

See below for guidance documents specific to gray literature searching.

Grey Literature Sources

Gray Literature Resources

Grey Literature Sources