Grey literature is any type of literature that is not produced by commercial publishing.
Grey literature includes (but is not limited to):
- theses and dissertations,
- conference papers,
- research data,
- clinical trials,
- diaries and letters,
- company records
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- government and NGOs' documents, reports and working papers
- eprints or pre-prints
- social media posts
- ephemera - e.g. brochures, pamphlets
- patents and IP.
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Whether grey literature should be included can depend on the level of the study, nature of the topic, how comprehensive the topic is and time available to complete the review.
- Reviews completed for honours degrees should usually concentrate on using published sources.
- Reviews completed for PhDs and further research should consider whether grey literature should be used.
- Some topics should include grey literature, especially when the topic may include aspects of policy or practice.
- Another type of grey literature that may also be included in medical research are registered clinical trials.