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Systematic Reviews: Grey literature

What is grey literature?

Grey literature refers to both published and unpublished research material that is not available commercially. A review can be biased when it fails to report crucial information that may be hidden in some grey literature. A search of grey literature is one way to address potentially biased reporting of research results in published material.
Some examples of grey literature are:

  • conference papers/conference proceedings
  • theses
  • clinical trials
  • newsletters
  • pamphlets
  • reports
  • fact sheets, bulletins
  • government documents
  • surverys
  • interviews
  • informal communication (e.g., blogs, podcasts, email),

Grey literature can be the best source of up-to-date research on some topics such as vaccination for children in remote areas of Australia. Note however that grey literature is usually not subject to peer review and must be evaluated accordingly.

How do I evaluate grey literature?

A checklist for evaluating grey literature has been developed by Jess Tyndall, Flinders University.

It uses AACODS (Authority, Accuracy, Coverage, Objectivity, Date and Significance) to evaluate grey literature materials.

  • Authority - Is the author credible?
  • Accuracy -  Is it supported by documented and authoritative references? Is there a clearly stated methodology? Is it in line with other work on the same topic
  • Coverage - Have limitations been imposed and are these stated clearly?
  • Objectivity - Can bias be detected?
  • Date - Can't find the date? Rule of the thumb is to avoid such material
  • Significance - Is it relevant? Would it enrich or have an impact on your research?

For a full version of this checklist please see this document. 

Where do I look for grey literature?

There are a number of sources where grey literature can be found. These include:



  • WorldCat which holds millions of holdings from numerous libraries world-wide
  • Large libraries like the Australian National Library which often collect grey literature in paper form


The Internet is now a major source for dissemination and retrieval of grey literature and often is a good starting point to a topic area:

How do I search for grey literature?

  • Since there are two accepted spellings, to locate information on gray/grey literature in general, search for : (gray OR grey) literature
  • Search the online catalogue of large libraries
  • Conference papers that have been published in a book or as a special issue of a journal can be easily obtained through library catalogues. Conference papers or conference proceedings that are unpublished are a lot more difficult to track down
  • A few databases are now indexing conference papers and conference proceedings. They include:
    • Web of Science
    • CINAHL 
  • ProQuest Dissertations and Theses, OAIster, Trove are a few sources that can be searched for national and international theses and dissertations
  • Contact authors, peer groups and private companies. This can be done through:
    • written correspondence
    • email discussion lists
    • the "institution" field of databases

Web search tips:

  • Most of the grey literature available on the Web is in the form of PDF documents. Also consider restricting your search to the .org and/or .gov domains. To search the Internet:
    • Go to Google
    • Enter your search term e.g. vaccination rural Australia filetype:pdf or vaccination rural Australia site:org in the Search box
    • Click on Search

Most grey literature is free. However some sources such as market research firms charge for access to their material.