What is grey literature?
The term grey literature "is usually understood to mean literature that is not formally published in sources such as books or journal articles" (Lefebvre, Manheimer, & Glanville, 2008, p. 106). Grey literature is a key source of evidence and argument in many subject areas and can include:
Why is grey literature important?
Grey literature helps you to form a more complete view of all the evidence around a particular topic. It is particularly important to include as part of your systematic review in order to limit bias due to publication lag and the publication of only positive results.
A systematic review conducted in 2008 by members of the Cochrane methodologies team found that often the results from grey literature significantly affect the outcome of a review, as they often report more negative or inconclusive data than published journal articles (Hopewell et al., 2008). As such, it is important to treat grey literature as another potential source of studies for inclusion.
Searching for grey literature
Hopewell S, McDonald S, Clarke MJ, Egger M. Grey literature in meta‐analyses of randomized trials of health care interventions. Cochrane Database of Systematic Reviews 2007, Issue 2. Art. No.: MR000010. DOI: 10.1002/14651858.MR000010.pub3. Available from: http://onlinelibrary.wiley.com/o/cochrane/clsysrev/articles/MR000010/frame.html
Lefebvre C, Manheimer E, Glanville J. Searching for studies. In: Higgins JPT, Green S, editors. Cochrane handbook for systematic reviews of interventions. Chichester: Wiley-Blackwell; 2008.
There are a number of sources available to search for grey literature. Access to most grey literature is free (or can be freely accessed via library databases). For additional sources in your subject area please contact your Faculty librarian.
CORE. a collection of open access research papers
To effectively search for grey literature using Google we recommend using Google Advanced Search.
Here you can enter your search terms and apply limits in the 'Narrow your results' section. For example:
Site or domain
For more information about refining web searches see Google Search Help.
For more information about searching Google see our guide on Using Google and Google Scholar.
Grey literature is usually not subject to peer review and should be evaluated accordingly. To assist with evaluation you may wish to refer to the AACODS checklist created by Jess Tyndall, Flinders University, covering: