When performing a systematic review, the comprehensive search for evidence should include grey literature. The Third International Conference on Grey Literature in 1997 adopted the Luxembourg Definition of grey literature is as follows: "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.” Grey literature typically includes reports, policy briefs, newsletters, conference proceedings, theses, and dissertations.
Because it is not created by commercial publishers, grey literature is hard to locate and as a result, major databases are not able to search it and provide reliable access. However, for many scientists, especially in fields in which knowledge changes rapidly, grey literature is often a primary means of communication and an important source of information.
There are numerous resources for finding grey literature, including the following:
