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Systematic Reviews: Grey Literature

Grey Literature

The term 'grey literature' is used to describe a broad and diverse range of different information that is produced and disseminated outside of commercial and academic publishing. Examples include, but are not limited to: Government papers, conference proceedings, NHS reports, briefings, charity websites, dissertations and theses, newsletters, press releases, and blogs.

To supplement research from other (university subscribed) information sources such as academic databases.

Some statistical and current practice information (e.g. patient information, policies etc.) may not be found in academic journals/databases.

Researchers should be aware that academic sources have often undergone a rigorous screening process to be included in specific databases. Grey Literature may not have undergone the same level of scrutiny and therefore researchers should question;

  • What type of resource is it?
  • What is the content? Is it relevant to my topic?
  • Why was it produced? Is it objective?
  • When was it produced?
  • How was this information produced? Does the author include references?
  • How was the data collected?
  • Where was it published?
  • Who wrote it?
  • Who is the target audience?

One example of a framework that could be used to help evaluate Grey Literature is the CRAAP Test.

Currency - how up to date is the information? is there anything more recent?

Relevance - is it relevant to your needs?

Authority - how credible is the creator/publisher of the information?

Accuracy - how accurate, reliable and truthful is the information?

Purpose - why was it created? To inform? To convince? To sell?

This was created by Sarah Blakeslee from the Meriam Library California State University

Many sources of Grey Literature are not designed for in-depth searching and will work differently to academic databases. They are often designed for anyone of any ability to search, especially if the Grey Literature you are using is openly accessible to anyone on the internet.

Although searching for Grey Literature can seem a less nuanced activity than searching for peer reviewed material; however, you still need to think carefully about your search strategies. You should keep track of

  • What keywords you search for
  • What resources you have searched (including the ones you may later exclude)
  • What types of information you have found
  • How you plan to use what you have found

When searching Grey Literature, you will often be restricted to simple searches.

Try to use similar keywords to your previous searches, however, you may have to accept that there is limited functionality. Avoid putting lots of search terms in the search box if there are few options to refine the results.

You can explain in your methodology why you have had to adapt your search strategy for each specific resource. Your examiners/tutors/collaborators know that Grey Literature cannot always be searched to the same granular detail as academic databases.

Important – please be aware that webpages and thus, many Grey Literature sources, can change or completely disappear very quickly. Therefore, we recommend that you take screen pictures of your searches/results in addition to saving the URL in case the URL ceases to work in the future. Always make a note of the last accessed date for the URL and include this in your referencing.

Referencing Grey Literature requires a judgement about the type of material we are using, for example whether it is:

  • A report from an organisation
  • Guidelines
  • Social Media or a blogpost
  • Newsletters

Whatever you use you must keep a note of the fundamental aspects of the resource. This includes Author, Title, Date, Source etc.

Some sources you find on Google Scholar will allow you to import the reference into referencing software such as EndNote. If you find that this option is not available, you can manually add the details into EndNote by creating your own record. If you are unsure which template to use, the Library’s Referencing Guide at the University of Manchester has further details and examples of what pieces of information should be collected. You should try and collate as many of the appropriate details as possible so that other readers do not struggle to locate the source for themselves.


It is not compulsory to use referencing software. EndNote is the software supported by the University of Manchester, however, there are other software products available. You may have your own method of organising your records that works for you.

Database directory

You can use our Database Directory to browse a broader range of databases that are relevant to Medical and Human Science Studies as well as other subjects. The directory is arranged alphabetically. You can refine this by subject or information type which allows you to identify databases that provide access to specific types of resources (e.g. Full Text Articles, Streaming Video, Theses and Dissertations, and much more).

You will also find the databases for your subject listed on the Subject Guides on the databases tab within these. It important to realise that many Medical and Human Science subjects  are in actual fact multi-disciplinary and it may be useful for you to look at related disciplines to your own.

Some database platforms have their own collections of full text resources embedded within the specific databases, however you may need to use the Find It@MCR link to locate all of our full text holdings.

Some platforms will produce their own collections of E-Resources in one product, for example PsycArticles, Elsevier Science Direct. These are useful if you wish to focus on locating a few articles quickly, however it is important to note that these only index the products they hold full text for and you must use the Find It@MCR link to locate all of our full text holdings if you are conducting an exhaustive search for in-depth research.

Clinical Key is a collection of four separate resources that contains videos of presentations and lectures on specific medical topics by experts in that field. We have Clinical Key for Nursing and Midwifery, Medicine, Dentistry and Pharmacy.

Theses and Dissertations can be found in some databases such as Web of Science, Scopus and some of the Proquest platform resources.

Overton spotlight

Overton

Overton is the world’s largest collection of policy documents, parliamentary transcripts, government guidance and think tank research. Overton collect data globally from 188+ countries and territories and in many different languages. There are over 12 Million documents indexed in Overton, and hundreds of new documents are added each day. Overton index these documents to make them searchable, organize them into categories and analyze them to extract key terms and topics.

Further information about searching Overton can be found here; Advanced searches - Overton Knowledge Base.

Key Grey Literature databases

Grey Literature websites

  • Google Scholar is a more refined product than Google because it focuses on academic sources of information of any discipline. It will include articles, theses, books, abstracts and court opinions, from academic publishers, professional societies, online repositories, universities and other web sites.
  • Ethos is a database but is currently directing people to British Library due to major technical outage).
  • British Library is the national library of the UK. British Library houses over 170 million physical items relating to any discipline, including books, newspapers, maps, sound recordings, patents and stamps.
  • Epistemonikos is a collaborative, multilingual database of health evidence. It is the largest source of systematic reviews relevant for health-decision making, and a large source of other types of scientific evidence.
  • Open DOAR comprises of a global Directory of Open Access Repositories which is hosted by JISC. The repositories provide quality-checked open access to academic outputs and resources. OpenDOAR launched in 2005 as the product of a collaborative project between the University of Nottingham and Lund University, and was funded by OSI, Jisc, SPARC Europe and CURL.Each repository record within OpenDOAR is reviewed and processed by a member the OpenDOAR editorial team.
  • OPENGREY.EU was formerly known as Open Grey. This brought together Grey Literature resources that had ceased such as SIGLE (System for Information on Grey Literature in Europe) which covered  pure and applied natural sciences and technology, economics, social sciences, and humanities and OMNI (Online Medical Networked Information) which focused on medical sources.
  • Policy Commons gives acceass to policy documents such as government papers both nationally and internationally. Policy Commons claims to be the world's most comprehensive policy database, with over 17 million reports from 41,000 think tanks, agencies and governments.
  • Semantic Scholar is a free and open access database, supported by the Allen Institute for AI. It provides free, AI-driven search and discovery tools and indexes over 200 million academic papers. 

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