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J Clin Epidemiol. 2006 Dec;59(12):1303-11. Epub 2006 Jul 11.

Limited search strategies were effective in finding relevant nonrandomized studies.

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  • 1Institute for Work and Health, 481 University Av, Suite 800, Toronto, Ontario M5G 2E9, Canada.



Searching for nonrandomized studies in electronic databases is complicated because there is a variety of study designs and lack of standardization in the terminology. The purpose of this study was to develop and evaluate a method to limit search strategies according to study design of comparative nonrandomized studies (cNRSs).


Four updated Cochrane systematic reviews that included nonrandomized studies (cohort, case-control, and cross-sectional studies) of the effects of health care interventions were selected. Search strategies limited to study design were devised for each one of these topic areas in two electronic databases (MEDLINE and EMBASE). A progressive method (PM) and a fixed method for selecting the most appropriate search terms associated with study design of nonrandomized studies are suggested.


The results showed that the sensitivity of search strategies (in two databases combined) limited to study design were between 90% and 100% for the PM using both controlled vocabulary (CV) and textwords (TWs) and between 95% and 100% for a fixed set of controlled vocabulary and TWs.


It is possible and acceptable to use search strategies limited to study design of cNRSs of health care interventions.

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