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Knowledge Synthesis: Systematic, Scoping & Other Reviews

Sources to Find Studies

All applicable sources need to be searched to locate studies and eliminate bias.  Consult with a subject librarian or find suggestions from 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.

Database Tutorials

PubMed for Systematic Reviews

We recommend Ovid Medline, rather than PubMed, for systematic reviews for several reasons. Ovid Medline allows you to:

  • easily read your search, because terms are on separate lines
  • use adj operator for proximity searches
  • discover relevant MeSH terms more easily (PubMed's mapping functionality is often more limited)

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.

See also: 

MEDLINE, PubMed, and PMC (PubMed Central): How are they different?

Ovid's Medline Compared To PubMed

If you are searching "Epub Ahead of Print, In-Process & Other Non-Indexed Citations, Ovid MEDLINE® Daily and Ovid MEDLINE® 1946-Present" effectively, there is no reason to ALSO search PubMed. Ask your librarian for details.

Grey Literature

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.


Preprints are manuscripts which may have been submitted to a journal, but not yet published. They have not yet gone through a formal peer review process, but some preprint servers do allow other researchers to post comments.

Preprint Repository Table

Forward and Backward Reference Chaining

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 and Consulting Experts

Handsearching means manually looking through journals of interest to check that nothing was missed when searching licensed databases. For your topic, ensure that key journals are either adequately indexed in the databases you're searching, and if not, consider handsearching (ask your librarian if you need help determining where a journal is indexed).

Another idea for uncovering unpublished research is to identify key researchers working on your topic of interest to identify studies in process. For instance, you might be able to get additional data on a study described in a clinical trials register or conference abstract, or on a review protocol.