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Select your databases

Library Guides (LibGuides)

For each discipline there is a subject library guide with selected literature databases and useful resources, compiled by the University of Groningen Library.

Go to the Library Guides.

Grey Literature

"The term ‘grey literature’ is often used to refer to reports published outside of traditional commercial publishing. Review authors should generally search sources such as dissertations and conference abstracts" (Higgins et al. 2019, section 4.3.5). Grey literature may include research reports, conference papers, dissertations and theses, clinical trials, government documents, census data, standards, patents, and other research outputs.

Grey literature has traditionally been considered somewhat difficult to locate, but it is important to consult these unpublished studies to reduce the risk of publication bias in results. 

More information about searching Grey literature for systematic reviews is on this page.

Reference: Higgins, J. (2019) 'Searching for studies' in Higgins, J. and Thomas, J., eds., Cochrane handbook for systematic reviews of interventions [online], Version 6, available: [accessed 27 May 2020].


Databases for citation searching

Citation searching is: take a publication, and search for articles and other publications by which it is cited. This can reveal important relationships that may not be found by other ways of searching.

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Handsearching involves the page-by-page examination of relevant journal issues, conference proceedings and other publications for relevant studies. In addition, the checking of reference lists of journal articles and other documents retrieved from a search.

Why is handsearching important?

  1. Locates relevant items poorly indexed or not indexed at all. Some databases do not comprehensively index all content in journal issues, or may not index at all supplements, special issues, or conference abstracts

  2. Allows researchers to scan content quickly for relevant studies from high-impact journals

  3. Ensures that relevant studies are not overlooked. (HLWIKI Canada)

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Subjects: Information Literacy, SmartCat, Systematic Review, OER, Fake news