Systematic Review Guide

Grey Literature is literature that is not published in the traditional sense such as clinical trials data, government documents, theses, conference proceedings. It is important to include grey literature in your review in order to broaden its scope, reduce publication bias, and include emerging research.

We are often asked what database to search for grey literature. The truth is that there isn't just one and it depends on the topic. Consider your topic and its stakeholders. Checking the publications written by organizations and associations relevant to your topic is a good way to start.

Here are some starting points for grey literature searching:

• Grey Literature Search Guide from the University of Toronto Libraries 
• Grey Matters: A Practical Tool for Searching Health-Related Grey Literature CADTH's Directory of grey literature producers, with a focus on health technology assessment and drug resources.
• OpenGrey Information on Grey Literature in Europe and access to 700.000 bibliographical references of grey literature (paper) produced in Europe and allows you to export records and locate the documents.
• Bonato S. Searching the Grey Literature : A Handbook for Searching Reports, Working Papers, and Other Unpublished Research [e-book]. Lanham, Maryland: Rowman & Littlefield Publishers; 2018.

• ClinicalTrials.gov is a registry and results database of publicly and privately supported clinical studies of human participants conducted around the world.
• European Union Clinical Trials Register contains information on interventional clinical trials on medicines conducted in the European Union (EU).
• ISRCTN registry is a primary clinical trial registry recognized by the WHO and ICMJE that accepts all clinical research studies (whether proposed, ongoing or completed), providing content validation and curation and the unique identification number necessary for publication.
• WHO International Clinical Trials Registry Platform (ICTRP) The main aim of the WHO ICTRP is to facilitate the prospective registration of the WHO Trial Registration Data Set on all clinical trials, and the public accessibility of that information.

• CADTH (Canadian Agency for Drugs and Technologies in Health) is a Canadian independent, not-for-profit organization responsible for providing health care decision-makers with objective evidence.
• European Medicines Agency is a decentralised agency of the European Union (EU), located in London. It began operating in 1995. The Agency is responsible for the scientific evaluation, supervision and safety monitoring of medicines in the EU.
• Devices @FDA is a catalog of cleared and approved medical device information from the United States Food and Drug Administration (FDA). It includes links to the device summary information, manufacturer, approval date, user instructions, and other consumer information.
• Drugs@FDA provides information about FDA-approved brand name and generic prescription and over-the-counter human drugs and biological therapeutic products. Drugs@FDA includes most of the drug products approved since 1939.

Conference papers, abstracts, and proceedings are included some databases such as Embase, Scopus, and PsycINFO. There are also specific conference proceedings databases such as  Conference Proceedings Citation Index (part of Web of Science Core Collection), available through subscription. 

You can also search individual conference proceedings to locate relevant papers.

• ProQuest Dissertations & Theses Global (by subscription only)
• Networked Digital Library of Theses and Dissertations, NDLTD
• Thesis Canada Portal 

Researchers may decide to search Google Scholar for studies but may sometimes limit to a certain number of results such as the first 100 or 200.

Google Scholar searches may retrieve grey literature not indexed in conventional academic databases. Keep in mind that Google Scholar is a search engine not a bibliographic database.

Google Scholar has an “Advanced Search” which can help focus the vast number of results. Click on the menu icon in the top left corner to access. See also Google Advanced Power Search Quick Reference.