Search hedges are used to find a higher number of articles about your topic. Search hedges are made up of subject headings, keywords, and synonyms separated by the word OR. Search hedges should be used carefully as they are database specific.

• View more example on the University of North Carolina systematic review guide.

Multiple researchers (Anders, Evans, 2010; Boeker et al, 2013; Haddaway et. al, 2015; Gusenbauer and Haddaway, 2020) have found Google Scholar to be an inadequate source for scholarly articles for systemic reviews in the medical field.  Anders & Evans (2010) did a side by side comparison with Google Scholar PubMed and found that Pub Med had better recall and precision in results than Google Scholar and concluded that PubMed's ability to create exact clinical searches with specific medical terminology gave it a significant advantage over Google.  When Haddaway et al examined Google Scholar's strength in searching for gray literature they found that it could not compete with a strong Web of Science search; GS still missed important literature in their estimation (2015).  Overwhelming, researchers recommend Google Scholar only be used in addition to other traditional academic databases.  

For non medical fields, Google Scholar may be a good supplmental choice, particularly for grey literature. However, Gusenbauer and Haddaway (2020) goes as far as to say "Google Scholar's extraordinary coverage acting as a multidisciplinary compendium of scientific world knowledge should not blind users to the fact that users' ability to access this compendium is severely limited, especially in terms of a systematic search. Google Scholar does not publically disclose their search engine's althogrims, nor do they accurately explain what is included in their search results" (211).  Google Scholar's search interface lacks most of the features systematic reviewers find the most useful including commanded line searches, saved history and consistency in results. 

If you would like to use Google Scholar in your systematic reviews as a supplement, please consider speaking to a librarian to make sure you are using Google Scholar to its fullest potential.

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Works cited

Grey literature sources include things like conference proceedings, dissertations, reports, clinical trials, and more. When you begin your systematic review and are determining the scope of your research, you'll decide whether or not to include grey literature in your review. The inclusion of grey literature is common in business, economics, and political science disciplines. A subject librarian can advise you where to search for grey literature.