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Health Info Libr J. 2011 Sep;28(3):210-5. doi: 10.1111/j.1471-1842.2011.00936.x. Epub 2011 Mar 30.

Developing a geographic search filter to identify randomised controlled trials in Africa: finding the optimal balance between sensitivity and precision.

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South African Cochrane Centre, Medical Research Council, Tygerberg, South Africa.



Research on identifying trials using geographic filters is limited.


To test the sensitivity and precision of a filter to identify African randomised controlled trials (RCTs).


We searched medline and embase for RCTs published in 2004 using a Cochrane filter for RCTs. The search was limited to HIV/AIDS but irrespective of location. Two investigators independently identified African RCTs from the retrieved records forming a reference set. We then repeated the search using an African geographic filter comprising country and regional terms forming the filter set. We compared the sensitivity and precision of the sets.


The medline reference set comprised 1799 records with 23 African RCTs; for embase, the reference set comprised 763 records with 37 African RCTs. The medline filter set comprised 180 records with 17 African RCTs; the embase filter set comprised 98 records with 27 African RCTs. Sensitivity of the filter was 74% (medline) and 73% (embase). Addition of the filter improved precision from 1.3% to 9.4% (medline) and from 5% to 28% (embase).


The African filter improved precision with some loss in sensitivity. Incomplete reporting of trial location in electronic bibliographic records restricts efficiency of geographic filters. Prospective trial registration should alleviate this.

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