Grey literature refers to a diverse array of information that is generated outside of conventional publishing and distribution methods, often lacking proper representation in indexing databases (i.e. search engines).
Grey literature can include unpublished surveys, government reports and publications, conference proceedings and abstracts, policy briefs and white papers, theses and dissertations etc. View an extensive list of Document Type in Grey Literature.
The approach to including and searching for grey literature will vary significantly depending on the nature of your research question, necessitating a tailored strategy that aligns with the specific characteristics associated with your area of investigation.
Finding grey literature involves exploring various non-conventional sources and repositories. Here are some effective ways to locate grey literature:
Conduct comprehensive searches using search engines like Google Scholar, Google, and other scholarly databases. Include specific keywords and phrases related to your research topic to uncover relevant grey literature.
Tips to find grey literature in Google Scholar (adapted from Haddaway et al., 2015):
1. Substantially more grey literature is found using title searches in Google Scholar than full text searches.
2. It is suggested that the greatest volume of grey literature in searches occurs at around 35 pages for title searches in Google Scholar. It is found that majority of grey literature begins to appear after approximately 20 to 30 pages of results.
Steps for Structured Grey Literature Google Searching
Going to Google Advanced Search and limiting search results from a specific region is one of the easiest ways to access a varying range of grey literature hits.
Limit to File Type
Limiting the file type to Adobe Acrobat PDF or MS Word may be especially good for structuring a search to only retrieve hits with more detailed content, such as evidence briefs or white papers.
Limiting by search domain is another means to exclude search hits from ir- relevant sources, such as commercial sources
Government and NGO Websites
Check government websites, policy institutes, and non-governmental organization (NGO) platforms for reports, policy papers, and research studies related to your topic of interest. Here are two database platforms that are supported by google search system.
Explore the repositories of academic institutions, universities, and research organizations, which often house theses, dissertations, technical reports, and other unpublished research materials.
ProQuest has developed a Dissertations Data Repository that can be helpful in identifying grey literature from dissertations and theses.
Look for conference proceedings and abstracts from academic conferences, as these can often contain valuable research findings and studies that have not yet been formally published.
Where to find conference proceedings:
Professional Associations and Societies
Visit the websites of professional associations and societies within your field, as they may publish reports, white papers, and other forms of grey literature.
Preprint servers where researchers may share preliminary findings, unpublished manuscripts, and other forms of grey literature. Following are some helpful preprint servers in social sciences:
Knowing when to stop searching for grey literature can be a nuanced decision and may depend on several factors. Here are some considerations to help you determine when it might be time to conclude your search:
Read Kastner et al., 2007 to read more on "stop searching" strategy in systematic reviews.
Advantages of including grey literature
Limitations of Grey Literature
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