Grey Literature is:
"That which is produced on all levels of government, academics, business and industry in print and electronic formats, but which is not controlled by commercial publishers."
-The Fourth International Conference on Grey Literature in Washington, DC 1999
This video presentation(3:00) introduces Grey Literature.
The inclusion of grey literature and unpublished reports in literature reviews is encouraged, particularly in certain topic areas such as public health. However, as with any other study reports, it is necessary to critically evaluate grey literature materials for the authority of the source, any potential for bias, reliability and reproducibility of study methodology and completeness of reporting. (See also the University of Louisville's research guide on "Evaluating Information Sources" at http://louisville.libguides.com/evaluation.)
Lister Hill Library