All applicable databases and indexes need to be searched to locate studies and eliminate bias. Use the links below or suggestions from other UBC Library research guides to locate key resources.
There are two key types of sources to search - licensed databases and alternate sources. Techniques for finding alternate sources include searching sources for grey literature; backward and forward reference chaining; hand searching; and contacting experts in the field.
Below are some health databases which are commonly included in systematic reviews. (See the Online Tutorials box for You Tube videos on searching Medline and CINAHL)
The UBC Library Research Guide for your discipline will also have more suggestions.
We recommend Ovid Medline, rather than PubMed, for systematic reviews for several reasons. Ovid Medline allows you to:
Some systematic reviews state in their methods section that they've searched both Medline and PubMed. However, there's nearly complete overlap between Ovid Medline and PubMed so there's generally not a need to search them independently.
Should you prefer to search PubMed for your systematic review, consider contacting your subject librarian for help devising your search strategy.
Google Scholar can be useful for finding grey literature, but this 2015 study suggests that it shouldn't be the only source searched:
Haddaway NR, Collins AM, Coughlin D, Kirk S (2015) The Role of Google Scholar in evidence reviews and its applicability to grey literature searching. PLoS ONE 10(9). doi:10.1371/journal.pone.0138237
Note that you'll need to take a different approach to building search strategies in Google and Google Scholar than in many other databases:
For more details, see:
Bramer WM, Giustini D, Kramer BM, Anderson P (2013). The comparative recall of Google Scholar versus PubMed in identical searches for biomedical systematic reviews: a review of searches used in systematic reviews. Systematic Reviews 2(115). http://doi.org/10.1186/2046-4053-2-115
Grey literature refers to materials that aren't published in a traditional way, including dissertations, conference proceedings, clinical trials, and clinical practice guidelines. These sources aren't usually covered in regular licensed databases. Below are some tools for finding grey literature.
Check out the citations in the reference lists of major studies. Examine what later studies have cited significant studies in these lists by searching:
Handsearching means manually looking through journals of interest to check that nothing was missed when searching licensed databases. Suggestions:
Another idea for uncovering unpublished research is to identify key researchers working on your topic of interest to identify systematic reviews in process. Suggestions: