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Systematic Review Guide

This guide will help you navigate how to create a systematic review.

What is Grey Literature?

Grey literature is defined as: "...information produced on all levels of government, academia, business and industry in electronic and print formats not controlled by commercial publishing (i.e. where publishing is not the primary activity of the producing body) --(ICGL Luxembourg definition, 1997) (Expanded in New York, 2004)

  • Reports 
  • Conference Abstracts 
  • Dissertations & Theses
  • Registered Clinical Trials
  • Interviews 
  • Patents 
  • Newsletters
  • White Papers- government report on any subject or a detailed or authoritative report.
  • Technical Reports
  • Book Chapters

Who Produces Grey Literature?

"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, i.e. where publishing is not the primary activity of the producing body." (Schopfel, 2010)

  • Industry
  • Government Departments
  • Think Tanks
  • Scholarly societies & associations
  • Academia

Websites to Search for Grey Literature


  •, through the U.S. National Institutes of Health is a registry of federally and privately supported clinical trials conducted in the United States and around the world.  (included in Cochrane searches)
  • World Health Organization (WHO) International Clinical Trials Registry Platform: The Clinical Trials Search Portal provides access to a central database containing the trial registration data sets provided by global registries. It also provides links to the full original records.
  • WorldCat: The World's largest library catalog. Contains dissertations and theses.
  • GoogleScholar (not the best, can be a supplementary source, but not standalone): finds text from academic repositories which include theses and dissertations. Biased to show older articles that are most cited. Results change due to AI. Shows what is most popular versus what is most relevant to your study. Newer topics will not show at the top. Slow to index new articles (inconsistent). 
    • The minus sign can be used to exclude common publishers/websites/words/domains 
      • Examples: -springer, -taylor, -elsevier, -wiley, -ncbi, -sciencedirect, journal
    • May show citations that can only be obtained as physical books, meaning, you will not find a PDF of it online. 
    • If you are seeking articles from a specific geographical area, search organizations based in that area. 
  • Networked Digital Library of Theses and Dissertations: an international organization dedicated to promoting the adoption, creation, use, dissemination, and preservation of electronic theses and dissertations (ETDs).
  • NIH RePorter: An electronic tool that allows users to search a repository of NIH-funded research projects and access publications & patents resulting from NIH Funding
  • Native Health Database: The Native Health Database contains bibliographic information and abstracts of health-related articles, reports, surveys, and other resource documents pertaining to the health and health care of American Indians, Alaska Natives, and Canadian First Nations.
  • CORE from Open University in the UK (Open access papers)
  • Source to find information on Federally-supported research. Contains grey literature.


Why is it Important to Include Grey Literature?

  • Grey literature, or evidence not published in commercial publications, can make important contributions to a systematic review. 
  • 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. 
  • Reduces publication bias, increase reviews' comprehensiveness and timeliness and foster a balanced picture of available evidence.

Paez, A. Grey literature: An important resource in systematic reviews. J Evid Based Med. 2017 Dec 21. doi: 10.1111/jebm.12265. Epub ahead of print. PMID: 29266844.

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