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PolyU Library

Conduct a Literature Review

A guide to walk you through the process of doing a literature review

Grey Literature

Grey literature usually refers to the information produced outside of traditional academic publishing. They may not be easily reachable by searching Google Scholar or major indexing databases.

Examples of grey literature include: 

  • conference abstracts, presentations, and proceedings
  • preprints
  • patents
  • theses and dissertations
  • government reports
  • other unpublished reports, e.g. white papers, working papers


Why Grey Literature?

Grey literature can be an important source to support research in many disciplines. It helps researchers to:

  • find the latest update on emerging areas of research before the research is formally published in journal articles or books
  • identify more evidence - especially the research with negative results which are less likely to be published in journals; this is essential for research in health science.
  • find information from authorities, professional organizations who do not distribute their works through academic or commercial publishing. Examples are government reports, papers written by industry professionals.
Be aware that grey literature is not peer-reviewed, so the quality can vary. Do make sure to critically evaluate the sources before using the information. 



Where to Find Grey Literature?

Here are some resources to help you find different types of grey literature:

Visit this guide to find more sources of grey literature in health science.

Preprints are the author's original, unpublished versions of articles. There are plenty of preprint servers or repositories that collect preprints in different disciplines. You may find a (rough) list of them on this page.

Here are a few examples to help you find preprints:

These scholarly search engines also search for preprints:

Here are a few commonly used databases to find theses and dissertations, from PolyU and/or worldwide:

To look for government reports and reports that are available on websites, the quickest way is to Google and limit your search to a particular site or type of domain. You can use Google Operators to achieve this. 

Here are some examples:

Limit to a domain:   (to find documents on Hong Kong government sites)
site:org   (to find documents from 'organizations')

Limit to a site with words in a URL:   (to find information from World Bank sites)

Limit to a filetype:

filetype:pdf   (to find PDF documents)

To learn more about Google Operators, check out these sites:

Some article databases also cover conference papers. Here are a few examples: