Research Guides: Systematic Reviews & Other Syntheses: Grey Literature

Featured resource

Grey Matters: a practical tool for searching health-related grey literature by CADTH.

Introduction

Grey literature is the term used to describe literature that is not formally published as a book or journal article [1], including:

conference abstracts and papers,
preprints,
dissertations and theses,
governmental or private sector research,
ongoing or unpublished clinical trial data,
statistical publications,
internal reports or working papers,
technical reports.

Related library guides:

In addition to the information provided about grey literature on this page, there are related library guides on:

Finding Theses and Dissertations,
Government Information (Health),
Public Health, which has a page on grey literature with additional sources to search.

Grey Literature Resources

Some library databases contain grey literature in addition to journal articles. For example, Web of Science Core Collection and Embase contain conference content, while PsycINFO and CINAHL contain some dissertations. Since health-related library databases do not generally provide comprehensive coverage of grey literature, other resources should be searched to identify literature that is not formally published as well.

Dissertations and Theses Databases

ProQuest Dissertations and Theses Global
Also available on the Web of Science search platform (see below).

The database offers full text for most of the dissertations added since 1997 and strong retrospective full text coverage for older graduate works. Over 130,000 new dissertations and theses are added to the database each year.

Designated as an official offsite repository for the U.S. Library of Congress, PQDT Global offers comprehensive historic and ongoing coverage for North American works and significant and growing international coverage from a multiyear program of expanding partnerships with international universities and national associations.

ProQuest Dissertations & Theses Global offers access to the full range of ProQuest Dissertations & Theses Full Text content plus additional international content (over 1.5 million PHD dissertations in overall). It also includes ProQuest Dissertations & Theses - UK & Ireland, which grants access to over 500,000 abstracts from UK & Irish PhD theses (the content from ProQuest Dissertations & Theses - UK & Ireland database).

For more information, please consult the guide.

Date Coverage: 1861 - present
ProQuest Dissertations and Theses Index on Web of Science

Provides access to 4 million citations to dissertations and theses from around the world from 1861 to the present day together with over two million full text dissertations that are available for download in PDF format. The index links to the full-text of the dissertation or thesis on the ProQuest platform, when available.

The database offers full text for most of the dissertations added since 1997 and strong retrospective full text coverage for older graduate works. Over 130,000 new dissertations and theses are added to the database each year.

Designated as an official offsite repository for the U.S. Library of Congress, PQDT Global offers comprehensive historic and ongoing coverage for North American works and significant and growing international coverage from a multiyear program of expanding partnerships with international universities and national associations.

ProQuest Dissertations & Theses Global offers access to the full range of ProQuest Dissertations & Theses Full Text content plus additional international content (over 1.5 million PHD dissertations in overall). It also includes ProQuest Dissertations & Theses - UK & Ireland, which grants access to over 500,000 abstracts from UK & Irish PhD theses (the content from ProQuest Dissertations & Theses - UK & Ireland database).

DART-Europe E-theses Portal

Preprint Servers and Databases

Preprint Citation Index
If various preprint servers are relevant for your topic, the Preprint Citation Index provides an aggregated search platform for nearly two million preprints from arXiv, bioRxiv, chemRxiv, medRxiv and Preprints.org. It is accessible via the Web of Science search platform.

Clinical Trial Registries

For quantitative systematic reviews of healthcare interventions, it is strongly recommended to search clinical trial registries (particularly ClinicalTrials.gov and WHO ICTRP) for on-going and unpublished trials in order to limit publication bias.

Note: Since August 2019, eligible reports of RCTs or quasi-RCTs from ClinicalTrials.gov and WHO ICTRP are being identified and systematically added to Cochrane CENTRAL. However, other study designs in these trial registries (e.g. cohort studies) are not identified and added to Cochrane CENTRAL.

Other Grey Literature Sources

COVID-19 Vaccine Grey Literature Resources

Google Scholar
Should you encounter a captcha problem, you can still search QUL resources by going to https://scholar.google.com following the instructions here.

Bibliography

Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. Available from www.cochrane-handbook.org.

Baudard M, Yavchitz A, Ravaud P, Perrodeau E, Boutron I. Impact of searching clinical trial registries in systematic reviews of pharmaceutical treatments: methodological systematic review and reanalysis of meta-analyses.. BMJ. 2017 Feb 17;356:j448. doi: 10.1136/bmj.j448.
Hartling L, Featherstone R, Nuspl M, Shave K, Dryden DM, Vandermeer B. Grey literature in systematic reviews: a cross-sectional study of the contribution of non-English reports, unpublished studies and dissertations to the results of meta-analyses in child-relevant reviews. BMC Med Res Methodol. 2017 Apr 19;17(1):64. doi: 10.1186/s12874-017-0347-z.
Schmucker CM, Blümle A, Schell LK, Schwarzer G, Oeller P, Cabrera L, von Elm E, Briel M, Meerpohl JJ; OPEN consortium. Systematic review finds that study data not published in full text articles have unclear impact on meta-analyses results in medical research. PLoS One. 2017 Apr 25;12(4):e0176210. doi: 10.1371/journal.pone.0176210.

Training Module

An inter-professional team led by Queen's has set out to develop an open access module series titled The Essentials of Conducting Systematic Reviews to introduce researchers to all stages of the systematic review process.

Check out Module 3: Searching for Eligible Studies.

Systematic Reviews & Other Syntheses