Documents that are considered grey literature can include the following: reports, white papers, technical reports, technical papers, technical briefs, working papers, discussion papers, policy papers, forecasts, or studies. In some circles theses and dissertations are included. Also, with the influx of digital repositories and OA sites, many of the documents found there are now thought of as being a part of grey literature.
Grey literature will be issued by various organizations, i.e., NGOs, IGOs, corporations, firms, professional associations, market and industry research firms, medical research centers, think tanks, federal, state, regional or local governmental departments and agencies and will be published irregularly or on an as-issued basis. Occasionally some may be published regularly if it’s part of a series. Even though some grey literature can be produced by specialized commercial firms, most grey literature will not by published by academic presses or commercial publishers.
The majority of this type of literature will be found in social science, science, business, health and medical and government related subject areas and will focus on scientific research, political topics, policy issues and social findings. Grey literature will often contain referenced citations and footnotes, etc. but might not be formally peer-reviewed. Also, they may not be indexed, provide citations or content that can be accessed in commercial databases, which makes them sometimes difficult to locate.
Critically evaluating all your sources is very important, especially when you include grey literature since these sources are most likely not per-reviewed, you will need to ask yourself:
Although grey lit is an important facet of research, be aware that various academic disciplines may place different values on this category of research. Consider these steps when deciding on whether to use grey lit or not.