3.6.3. Search filters

In systematic reviews, if time and resources allow, specificity is often sacrificed in favour of sensitivity, to maximize the yield of relevant articles. Therefore, it is not unusual to retrieve large numbers (possibly thousands) of bibliographic references for consideration for inclusion in an extensive systematic review. This means that reviewers may have to spend a lot of time scanning references to identify perhaps a limited number of relevant studies.

Search filters are available to focus the search according to the type of study that is sought, for example to focus on randomized controlled trials, diagnostic accuracy studies, prognostic studies or systematic reviews (see example in appendix). Specific search filters also exist for well-circumscribed clinical problems/populations, e.g. child health (Boluyt, 2008), palliative care (Sladek, 2007), or nephrology (Garg, 2009).

Sources of filters include:

• PubMed at the Clinical Queries screen
• InterTASC: http://www.york.ac.uk/inst/crd/intertasc/index.htm
• SIGN website: http://www.sign.ac.uk/methodology/filters.html
• HiRU: http://hiru.mcmaster.ca/hiru/
• OVID or Embase.com

During the selection of an appropriate search filter, aspects of testing and validation should play an important role. Specific appraisal tools are available to evaluate the methodological quality of search filters (Bak, 2009; Glanville, 2009).

For diagnostic studies, it is recommended not to use a search filter.