Grey literature is any literature that has not been published through traditional means. Grey literature may include reports, theses, conference proceedings, technical standards or government documents - essentially anything that is not created with commercial publication in mind.
Grey literature is often excluded from large databases and other mainstream searches so it can be hard to find. Leaving grey literature out of comprehensive literature searches excludes a major important section of the available research. To avoid bias and to ensure that that your literature review is as thorough as possible, always search for grey literature.
This page lists some best bet resources that are useful for finding grey literature.
A thorough grey literature search should involve a general sweep of the web by using different search engines. Google is an important search engine but other search engines, such as Yahoo and Bing, could also be useful.
While Google is a powerful tool for searching for grey literature it should not be used exclusively - other sources should also be searched in order to find grey literature.
Some tips:
1) Restrict content to .org or .gov sites
Type in your topic and then either "site:.org" OR "site:.gov"
2) Restrict content to file type
Type in your topic and then "filetype:pdf" OR "filetype:doc"
3) Limit your search to a specific geographic location (e.g., Australia or the UK)
4) Use the Duck Duck Go search engine which does not record your location or user searches
5) Use Link Klipper (Chrome extension) to pull results into a Microsoft Excel spreadsheet. You can also use the Grey Literature Search Log form linked below to keep track of your searches: