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Grey Literature and Other Sources: How to find grey literature

An overview of key search strategies to locate grey literature, informal or unpublished material. Provides sources and instructions on reporting requirements for systematic reviews.

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Planning your search for grey literature

Many Library databases include grey literature. You will also need to search using additional sources and approaches to ensure you do not miss anything crucial. To be systematic, adapt across the search strategy that you developed for your core database search, and ensure that your approach is transparent and where possible reproducible.

The Library's Guides provide links to discipline specific information sources such as databases, organisations, and more. 

How to find grey literature

Technique Description
Expand your search to other databases Some databases index material that is traditionally regarded as 'grey' literature, such as theses and reports
Undertake citation searching Check reference lists of reports of included studies ('backwards citation searching') and research outputs that have cited these reports in turn ('forwards citation searching')
Identify key authors and experts The author profiles of researchers working in the area may reveal further avenues (studies, organisations, contacts, etc.). Experts may be able to provide guidance
Undertake 'hand searching' View issues of relevant journals or conference proceedings
Examine relevant clinical guidelines These high quality summaries designed to assist health professionals make clinical decisions about appropriate health care can be a valuable source of studies
Search trials registers Locate ongoing or unpublished studies
Consult conference materials Conference material can be a source of the latest research and contain references to studies that are ongoing or for which outcomes were never formally published
Identify key organisations Identify government agencies, peak bodies, research institutes and other organisations relevant to your area of interest
Undertake web searching Use search engines, catalogues, portals, directories, and other tools to locate further material. Search websites of key organisations

Noteterminology has changed over time, and rather than using 'pearling' and 'snowballing' this is now more commonly referred to as backward citation searching (also known as reference list checking) and forward citation searching.

Finding grey literature can be difficult and time consuming.

Grey literature often:

  • is not classified, catalogued, indexed or archived
  • is not stored in a retrievable format
  • is not available electronically
  • has short print runs which may lead to lack of availability
  • has inconsistent format and citation information
  • has a large volume of material which may be overwhelming
  • has variation in evidence quality.

These challenges can make relevant information virtually impossible to find and eventually invisible.

Learn about backward and forward citation searching, hand searching, author searching and consulting experts.

Video Length: 7:16

  • Searching is an iterative process that will require evaluation, validation, verification, and revision.
  • You should look outside of your database searches to identify studies that you may have missed.
  • There are several techniques for validating and verifying your search:
    • Check the cited reference list of studies you have located. This is sometimes called pearling or cited reference searching.
    • Investigate whether other studies have cited the studies you have located. This is called citing reference searching.
    • Search for all studies conducted by specific authors that you have identified as experts in the area of interest. This is called author searching.
    • Review the table of contents of any relevant journals to find additional articles. This is called hand searching.
    • Consult experts in the field who may be able to supply you with a list of key articles.
  • If you find studies that were missed in your initial search, it is necessary to examine the reason why these studies were missed. You may need to revise your search strategy accordingly.
  • When examining why studies were missed, ask yourself:
    • Were the missed studies indexed by the databases I searched?
    • If no, should I search other databases that do index these articles?
    • If yes, why did I miss them? How are the missed studies indexed in the database? Did I overlook key subject headings?
  • After several rounds of validation, verification, and revision of your search strategy, you should now have a potentially exhaustive set of relevant studies you can review.

Guidelines and standards

Dedicated to grey literature

A selection of organisations, portals and tools that focus on grey literature: