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Literature reviews

Information providing guidance on starting a literature review, including resources, techniques and approaches to searching the literature and writing the review.

What is grey literature?

"Grey literature stands for manifold document types produced on all levels of government, academics, business and industry in print and electronic formats that are protected by intellectual property rights, of sufficient quality to be collected and preserved by library holdings or institutional repositories, but not controlled by commercial publishers." (Schopfel, 2010).


Schopfel, J. (2010). Towards a Prague definition of grey literature

Grey Literature Tutorial (2:39 mins) by Western University (YouTube)

Using grey literature in research

Grey literature:

  • encompasses a broad range of material
  • is not available in traditional channels of publishing and distribution
  • is not well represented in indexing sources

Using grey literature in research may help you:

  • include some alternative perspectives by encompassing a broad range of material
  • offset possible bias in published results
  • include more local information
  • fill in research gaps

Examples of grey literature

  • Blogs
  • Clinical trials
  • Conference papers and proceedings
  • Datasets
  • Diaries and Letters
  • E-prints or Pre-prints
  • Fact sheets, bulletins
  • Government and NGOs' documents, reports and working papers
  • Infographics
  • Informal communication
  • Interviews
  • Market reports
  • Newsletters
  • Pamphlets
  • Patents
  • Policy statements
  • Posters
  • Research Data
  • Social media posts
  • Standards
  • Statistics
  • Surveys
  • Theses

Searching Google for grey literature

Searching the internet can be useful to locate information not published within the main channels of literature indexing or supply. It is best to search within known sites or to use a search engine's advanced search features.

Google Advanced Search has a number of advanced search features which can make a search much more targeted. These features include searching by:

  • field
  • file type
  • domain

Field searching

To search for a word in the title of your search results use the intitle: command followed by the search term. For example: intitle:rhabdomyolysis

File type

Grey literature is often published online as a PDF or Word document. Using Google's filetype: search will help narrow down the results to these file types. For example - rainfall data filetype:pdf 

  • Document types include:
  • Word Documents .doc 
  • PowerPoint files .ppt,
  • Excel Files .xls
  • PDFs .pdf


A Google site search allows you to limit results to one website or domain rather than the entire internet. To perform a site search on Google enter your search words and add site: in front of the required URL.  For example -

The default for a government site is to use .gov and this defaults to a US government site, to make it an Australian government site add au, e.g. site:

All of these operators can be mixed together as a search. For example - food security filetype:pdf

General sources of grey literature


Directories and Repositories

Library catalogues

News articles

Patents, Standards and IP sources

Policy, Statistics and Data

Preprint archives

Preprint databases contain the author's original manuscript before submission for traditional publication. Find out more about preprints.


Evaluating grey literature

Grey literature should be appraised to the same standards as those used to evaluate any other literature. Grey literature sources often do not have the same quality checking as that of peer-reviewed literature. Careful examination is required to ensure the credibility of the source, the author and content.

The AACODS Checklist is an evaluation tool that provides guidance when using grey literature sources, incorporating the following ideas:

  • Authority - Incorporates expertise, propriety, experience, credibility, reliability: it asks the question who is responsible for the intellectual content?
  • Accuracy - Does it seem to be right? Has it used a clearly stated methodology? Has it been peer reviewed?
  • Coverage - Try to be aware of any coverage limitations, stated or otherwise.
  • Objectivity - This incorporates opinion, expert or otherwise. Is it balanced or does it have an unstated bias?
  • Date - Does the resource have a clear date related to content?
  • Significance - Is it meaningful? Does it add context?