Systematic review searching
Searching grey literature
- What is grey literature?
- Key grey literature sources
- Clinical trials & guidelines
- Googling for grey literature
Grey literature can be 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).
Grey literature can include:
- Technical or research reports from government agencies
- Reports from scientific research groups
- Working papers from research groups or committees
- Dissertations and theses
- Unpublished or ongoing studies
- Clinical trial registries
- Clinical practice guidelines not published in journals
- Conference and meeting proceedings/abstracts
- Informal communications with experts
- Reports identified via Google searching
Systematic frameworks for searching the grey literature
The Grey Matters online checklist tool produced by The Canadian Agency for Drugs and Technologies in Health (CADTH) is excellent when searching for drug evidence.
Health Technology Assessment on the Net: 2015, produced by the Institute of Health Economics (Canada), complements the CADTH checklist.
Another master list of grey sources is Databases for Research in Health, produced annually by Jess Tyndall at Flinders University.
The list, originally created to support primary health care and public health postgraduates, has been expanded to include clinical and biomedical resources. Websites are not included unless they have a strong searchable component, and the content is organised in such a way that it can be usefully interrogated by researchers.
Jess Tyndall is also the author of the AACODS checklist for evaluating the quality of grey literature.
Australian grey literature sources
International grey literature sources
Clinical trial registries
Searching clinical trial registries can be quite challenging. Usually very simple search strategies work best. This article looks at the usefulness of trial registries for SRs and optimal strategies for ensuring you don't miss key studies.
Glanville J, Duffy S, Mccool R & Varley D. Searching ClinicalTrials.gov and the International Clinical Trials Registry Platform to inform systematic reviews: What are the optimal search approaches? Journal Of The Medical Library Association. 2014 Jul; 102(3): 177–183.
Clinical practice guidelines
To effectively search the web using Google for grey literature of academic quality, use the Google Advanced Search option.
Google searching is rudimentary at best so you can only use a few of your search terms at a time.
Using the Advanced Search form:
- Enter one search term only from each of your concepts in the 'All these words' search box.
These terms should be the most important and precise ones from your search strategy. Google will combine these terms with AND.
- Include any important synonyms for these terms in the 'Any of these words' box.
These terms will be combined with OR.
- In the 'Narrow your results' section, choose 'English' for language and PDF for file type.
Most high quality grey literature is made available online as PDF documents.
- Consider restricting to a site or domain.
Useful ones include .edu or .ac for academic institutions, .org for organisations, and .gov for government sites.
Use this approach with caution as domain names vary by country and you can only search one domain name at a time.
An example Google Advanced Search
More tips on searching Google are available here: