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Grey Literature (in the Health Sciences)

Grey Literature Defined

Grey/Gray Literature deals with the production, distribution, and access to multiple document types produced on all levels of government, academics, business, and organization in electronic and print formats, not controlled by commercial publishing.  GreyNet International

These types of documents are not always collected into citation databases and often are not available for libraries to purchase, so finding and accessing grey literature is significantly more difficult than finding and accessing research articles. However, it is beneficial and often necessary to search one or more types of grey literature when creating comprehensive evidence syntheses like guidelines, systematic reviews, meta-analyses, and scoping reviews as the information contained in grey literature documents can provide broader/alternative perspectives and help to reduce biases, in particular publication bias.

This guide contains links to databases, search engines, and websites relevant to some of the more commonly searched types of grey/gray literature in the health sciences: policy positions, reports, briefings, evaluations of programs, white papers, clinical trials, regulatory information for drugs and medical devices, grants, theses & dissertations, conferences, documents from professional organizations, and statistics. Click here for a comprehensive list of grey literature document types. Resources listed in this guide are freely available, unless otherwise noted.

Since much of grey literature is unpublished or published through non-commercial avenues it can be difficult to find. For detailed guidance on how to search the grey literature, please see below.   

Guidelines for Searching Grey Literature

The resources below provide detailed guidance on how to approach searching grey literature and resources to search. 

Where to Begin?

The value that grey literature brings to a research question varies greatly from topic to topic.  As such, the decision around whether to include grey literature must be determined by each research team.

Although guidance exists around the the broad process of conducting a grey literature search, there is no "gold standard" to follow when  conducting a grey literature search. The following provides an example of elements to consider in order to get started with this process. Ultimately, every research team will have to tailor and develop a grey literature plan to best fit the needs of their specific research question. 

As the scope of grey literature is quite vast, research teams that decide to move forward with this process must narrow down what kind of documents are relevant to their research topic, keeping in mind inclusion and exclusion criteria. Establishing parameters / scope to searching is also necessary, taking into consideration resource limits such as team availability to conduct the identified searches and screen additional data.  

This diagram provides a visual representation of a potential grey literature search plan for a systematic review where the goal is to find information from clinical trials (Relevo, R. Searching the Grey Literature: Where To Look and What To Expect (Text Version), presented at AHRQ annual conference 2011). There are a few specific types of grey literature documents likely to include clinical trials information: trials registries, regulatory documentations, conference materials, and other miscellaneous resources such as reports from drug companies and professional pharmacy organizations. If a team had no constraints, they might search comprehensively for all of these types of documents using several search engines, but typically teams create a unique, individual plan that includes a few document types and a few search engines.

Researchers conducting systematic reviews in accordance with Cochrane MECIR guidance will want to:

Researchers may also consider:

  • forward citation searching: consult Cited by lists for included articles (Google Scholar, Web Of Science, Scopus) 
  • checking reference lists of any relevant systematic reviews identified
  • handsearching table of contents for specified journal titles (can be done electronically)
  • searching websites of specific organizations 
  • searching the internet
  • searching Google Scholar - see tips for searching Google Scholar
  • contacting experts in the field

Common literature to consider searching for in databases include: 

Researchers may also consider searching: 

Depending on the resource being searched some search results will be downloaded for screening (i.e. database searches) and others will be screened directly on the site (i.e. websites, internet search results). Either way, sufficient information should be documented to support consistent replicability of search results and detail for PRISMA flow charts. See PRISMA S - (Searching) for detailed support on searching many of the resources listed above. 

In general, consider documenting the following elements: 

  • date
  • resource searched (i.e. organization website or database name)
  • URL's
  • keywords / search strategies 
  • # of results (consider screen grabbing images of result pages when not downloading total results and screening directly on site)
  • # of items screened / any parameters; i.e. screening limited to first 5, 10, 20 pages, / 100 results, etc. 
  • # of citations selected 
  • settings; i..e. Google Scholar was searched in incognito mode to mitigate influence of search engine personalization on results   
  • The AACODS checklist, developed by Jess Tyndall, provides guidance for critical appraisal and evaluation of the Authority, Accuracy, Coverage, Objectivity, Date, Significance of grey literature. 
  • Documents found via grey literature searches can be added to Covidence.

Examples of Plans and Strategies for Searching Grey Literature

The resources below provide examples of how research teams have developed Grey Literature plans/approaches tailored to a specific research topic. 

Still have questions - contact a librarian for help starting your search of grey literature. 

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