Gray literature can include:
Government agencies, NGOs, businesses, academics and academic organizations, and many more produce gray literature. Some important sources of gray literature include:
Despite not having been vetted by others from the same field, gray literature tends to have:
Depth and Breadth: A thesis may contain data that is never included in the journal article that is ultimately published using its findings. In other cases, a broader view may be what is wanted, in which case a government factsheet or institutional newsletter targeted to a lay audience may meet the searcher's need.
Timeliness: Results of studies may appear in gray literature 12 to 18 months before being published via traditional channels.
Flexibility: Rather than waiting years for the publication of a revised edition, authors, editors, and Web content creators can update information when needed, a factor that reinforces the timeliness of gray literature.
Accessibility: Although governments and industries often restrict the readership of certain types of gray literature (classified or proprietary information, for example), there is also a great abundance of gray literature that is freely available to all, either in print or on the Web.
Less 'Positive Publishing Bias': Generally, in scholarly journals, positive, interesting research results get preferentially published, while in gray literature, one tends to also learn of negative research results - equally important to know about, which makes searching gray literature an important task during systematic reviews.
Finding and using gray literature can involve challenges such as:
Location -- the flip side of accessibility: While there is a great deal of gray literature that is freely available, it is often produced for a narrowly targeted readership, without the goal of gaining a wide audience. This can make it hard to index and catalog, which increases the difficulty of finding it. Furthermore, one man's flexibility is another's instability; something that was here (on the Web) today may be gone tomorrow.
Verification/Validation: You may need to free yourself of the mindset promoted in some academic disciplines of looking only to peer-reviewed work published in "reputable" journals. There is a great deal of information produced by both commercial enterprises and government agencies which lies outside of the scholarly realm yet is of high value.
Citation: You may be quite familiar with the citation styles for books and journal articles but feel mystified when faced with the need to cite a white paper, newsletter, or dissertation. Most if not all of these are discussed and examples given in the APA and other style manuals. Also, feel free to ask a librarian for help with this. Don't let a citation question stand in the way of referencing a valuable resource!
Collection/Preservation: Although this may not initially appear to be an end-user issue, it will ultimately become one. Libraries and other information repositories are faced with the huge challenge of choosing, out of the vast expanse of gray literature, what should be collected and in what medium/format it should be preserved. Likewise, in the print world, storage space can quickly become a limiting factor in the retention of gray literature. Remember: GRAY does not always STAY.
Trying the following Google search commands will help you find Gray Literature when searching in Google: