What is grey literature?

The wealth of knowledge and information produced by organisations, governments and industry, covering a wide range of subject areas and professional fields, not controlled by commercial publishing.

Grey literature is recognised as a key source of evidence, argument, innovation, and understanding in many disciplines including science, engineering, health, social sciences, education, the arts and humanities
(PISA Declaration May 2014).

Conference abstracts and other grey literature have been shown to be sources of approximately 10% of studies referenced in Cochrane Reviews (Paez 2017).

Some examples include:

Where to start

Grey literature can be hard to find. As a starting point we recommend the steps below, followed by browsing our list of search engines and other online sources:

Look for Conference proceedings

Embase contains conference abstracts

Other conference proceedings may require a more manual approach based on your team's knowledge of past conferences and whether the proceedings were published in hardcopy or are available online via a Google search. 

Look through the reference lists of existing reviews and publications on your topic

Authors of previous reviews may have referenced studies that were unpublished or included other relevant grey literature.

Contact experts and known authors in the field 

They may be aware of unpublished material addressing your question or ongoing studies.

Search clinical trial registries

Ongoing trials can also be located through clinical trials registries such as ClinicalTrials.gov, ANZCTR or the WHO international trials registry.

Documenting and appraising

Document your search

Because grey literature is rarely indexed it's important to keep clear records of exactly where you searched (note URLs), what terms you used and the date you accessed the item – we recommend a spreadsheet. We also recommend printing or keeping an electronic copy rather than relying on bookmarks - online material may be removed or edited after you have seen it.

Critical appraisal

As you locate grey literature you need a way to evaluate and critically appraise it - the AACODS checklist is one tool you could use.

Search Engines

Google Advanced

The best way to do a surface web search for grey literature – you can narrow down via domain (.edu, .gov etc) or specify terms such as “study” or “studies” or “control group” so you don’t get swamped with results. More information about searching Google Advanced. 

Mednar

Free, medically-focused deep web search engine providing a search of authoritative public and deep web resources. It is a US focused tool offering a Google like interface.

BASE

According to their site, BASE is one of the world's most voluminous search engines especially for academic web resources. BASE provides more than 120 million documents from more than 6,000 sources. You can access the full texts of about 60% of the indexed documents for free (Open Access). BASE is operated by Bielefeld University Library.

Online Sources

Grey Matters

A practical tool for searching health-related grey literature. Created and maintained by the Canadian Agency for Drugs and Technologies in Health, it provides impartial advice and evidence-based information about the effectiveness and efficiency of drugs and other health technologies in Canada and globally.

Health Services Research Projects in Progress (HSRProj)

Run by the National Library of Medicine (USA), provides information about health services research-in-progress before results are available in a published format.

OpenGrey

A multidisciplinary database with content from a range of European sites with research reports, conference papers, dissertations and other types of grey literature covering science, biomedical science, social science and humanities.

Grey Literature Report - The New York Academy of Medicine

Produced between 1999 - 2016, alerting readers to new grey literature publications in health services research and selected urban health topics. As of January 2017 the site is not being updated, but resources are still accessible. They also provide an online list of grey literature publishers.

Theses & Repositories

Trove (National Library of Australia)

Trove indexes almost a million theses; not all are available online. The National Library of Australia have developed a guide to assist with finding relevant theses in Trove.

OpenDOAR and ROAR

Two directories of open access repositories – use these to locate other repositories