Grey literature refers to both published and unpublished research material that is not available commercially.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:
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.
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.
For a full version of this checklist please see this document.
There are a number of sources where grey literature can be found. These include:
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:
Web search tips:
Most grey literature is free. However some sources such as market research firms charge for access to their material.