"There are many definitions of grey literature, but it is usually understood to mean literature that is not formally published in sources such as books or journal articles."
Cochrane Handbook 6.2.1.8
Clinical Trials registers
US Clinicaltrials.gov
ISRCTN registry
Primary clinical trail registry recognised by WHO and ICMJE.
National Institute for Health Research (NIHR) list of studies recruiting in the UK
Conference proceedings can be found in a number of databases that can be accessed from the library's databases list.
PhD theses and postgraduate dissertations can be useful grey literature.
Other sources
Through Overton you can find grey literature from leading global universities, IGOs, NGOs, research funders, publishers and think tanks, government reports and legislation. You can also trace the academic literature used in creating the policy documents.
NB: This database can be browsed on campus without signing into the Overton site. Off campus, users need to register on the Overton registration page with their @bristol.ac.uk email address. Overton allows users to discover policy documents in 180 countries and explore their links to each other and to the academic research that has informed them. Overton indexes work from governments, universities, IGOs, NGOs, research funders, publishers and think tanks to understand their role in the policymaking landscape. Users can track the evolution of ideas all the way from academic and think tank research to government reports and legislation.
Policy Commons could be another source of useful grey literature.
Use Policy Commons to discover and follow high-quality policy research from 210 countries and territories produced by world’s leading policy experts, charities, think tanks, IGOs and NGOs. Includes publications from inactive organisations that may not be available elsewhere. For help with searching see https://coherentdigital.net/resources2-1
Our Grey Literature quick reference guide has details of many sources of grey literature. It is available with our database guides to health and biomedical databases.
Hand-searching is also required in a systematic review. It involves checking within the Table of Contents of selected key journals or searching them in full text. This will identify any relevant articles that have been missed by the database searches. You can analyse your search results to identify key journals for the review. You will need to explain why you've hand-searched the particular journals and also indicate the year range of your search.
You should also check the references of articles that you are including in your analysis. You could do this via Web of Science (available via the Library's databases list) using the cited references function.
Next step: Managing your search results
Grey literature can be really useful because it is often more current - it bypasses the peer review/ publishing process which means that it can be useful when looking at new or emerging areas of research. However, as it's not peer reviewed it can be of variable quality. You will need to assess the quality of this information yourself and decide if it appropriate to include in your review. Below are some useful tools for evaluating the information your are looking at.
Mike Caulfield. CC BY 4.0, via Hapgood.US
STOP – What is the source of the information? What is the reputation of the information and the source?
INVESTIGATE – What are you reading? Who produced the information? Knowing the expertise and agenda of the source is crucial to understanding the significance and trustworthiness of the information.
FIND BETTER COVERAGE – look for trusted sources to verify the information – “go out and find the best source you can on this topic, or, just as importantly, to scan multiple sources and see what the expert consensus seems to be”
TRACE – try and find the original context for the information you are looking at. Viewing it in it’s original context will help you get a sense of how accurately the information it being presented.
Developed by staff from Meriam Library at California State University, the CRAAP Test looks at five criteria and suggests questions to ask yourself about of the criteria to help you establish the value of the work. Follow the link to see the full details for each of the criteria.
Currency
Relevance
Authority
Accuracy
Purpose
Meriam Library. CC BY 4.0, via California State University