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Systematic Reviews in the Health Sciences

What is grey literature?

Searching the grey literature by Relevo, R.

Grey literature refers to both published and unpublished research material that is not available commercially.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
  • surveys
  • 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.

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 evaluate grey literature?

A possible checklist for evaluating grey literature is using AACODS (Authority, Accuracy, Coverage, Objectivity, Date and Significance)

  • 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?