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Knowledge Synthesis

This guide includes content about systematic reviews, including general information and information about librarian assistance

What is Grey Literature?

"Gray literature, or evidence not published in commercial publications, can make important contributions to a systematic review. Gray literature can include academic papers, including theses and dissertations, research and committee reports, government reports, conference papers, and ongoing research, among others. It may provide data not found within commercially published literature, providing an important forum for disseminating studies with null or negative results that might not otherwise be disseminated. Gray literature may thusly reduce publication bias, increase reviews’ comprehensiveness and timeliness, and foster a balanced picture of available evidence." (Paez, 2017)

Read more

  • Cooper, C., Lovell, R., Husk, K., Booth, A., & Garside, R. (2018). Supplementary search methods were more effective and offered better value than bibliographic database searching: A case study from public health and environmental enhancement. Research Synthesis Methods, 9(2), 195–223.
  • Delaney, A., & Tamás, P. A. (2018). Searching for evidence or approval? A commentary on database search in systematic reviews and alternative information retrieval methodologies. Research Synthesis Methods, 9(1), 124–131.
  • Haddaway, N. R. (n.d.). The Use of Web-scraping Software in Searching for Grey Literature. Retrieved May 26, 2021, from
  • Haddaway, N. R., Collins, A. M., Coughlin, D., & Kirk, S. (2015). The Role of Google Scholar in Evidence Reviews and Its Applicability to Grey Literature Searching. PloS One, 10(9), e0138237.
  • Lee, M. S., Hughes, A., Lockmiller, C., Day, A., Brown, M., & Jenson, R. (2022). Working Together: How Academic Librarians Can Help Researchers Prepare for a Grey Literature Search for Systematic Reviews Involving Minoritized Populations. The Journal of Academic Librarianship, 102626.
  • Saleh, A. A., Ratajeski, M. A., & Bertolet, M. (2014). Grey Literature Searching for Health Sciences Systematic Reviews: A Prospective Study of Time Spent and Resources Utilized. Evidence Based Library and Information Practice, 9(3), 28–50.


Paez, A. (2017). Gray literature: An important resource in systematic reviews. Journal of Evidence Based Medicine. 10(3), 233-240.