Knowledge Synthesis: Systematic, Scoping & Other Reviews

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 for:

• Grey literature
• References by backward and forward chaining
• Sources by hand searching
• Sources by contacting experts in the field

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.

It is desirable to use grey literature in systematic and scoping reviews as published journals may be susceptible to biases against reporting negative or neutral outcomes, a phenomenon known as "positive result bias." Including grey literature or cross-referencing published studies with their grey literature counterparts (e.g. study protocols, clinical trials) can help combat various publication biases. See the UBC Library guide below for more information and for tools to help you find grey literature.

Citation searching, also sometimes referred to as 'citation chasing' or citation chaining', describes the search process used to exploit citation relationships to find additional articles beyond your database searches.

It is recommend to carry out citation searching once articles retrieved from the database searches have been screened and compiled into a list of included articles only. Citation searching methods can then be applied to papers that will be included in your review.

• Forward citation searching: retrieving and screening citing references.
  • Examine what later studies have cited significant studies.
• Backward citation searching (also referred to as 'reference list checking'): retrieving and screening cited references.
  • Check out the citations in the reference lists of major studies. 

See the TARCiS Statement (Terminology, Application, and Reporting of Citation Screening) for more information and citation searching reporting checklists.

Handsearching means manually looking through journals and/or journal websites of interest to check that nothing was missed when searching licensed databases. For your topic, consider handsearching specific journals that are not already indexed in the databases you are searching.

The UBC Journal Search function is a quick way to find the journals you need. Accessing journal websites in this way will help ensure you have access to any full-text articles you find.

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.

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 - sources and search tips