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clinmed/2000110001v1 (November 12, 2000)
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Evaluation of the usefulness of Internet searches to identify unpublished clinical trials for systematic reviews

Gunther Eysenbach

Objectives: To avoid selection and publication bias, systematic reviewers should employ a broad range of search techniques and make efforts to locate unpublished studies. We tried to establish whether searches on the World-Wide-Web are useful to identify additional unpublished and ongoing clinical trials by developing and evaluating a search strategy. Design: Seven Cochrane systematic reviews, where Internet searches were not mentioned as part of the search strategy, were selected as criterion (gold) standard. Their search strategies were retrospectively adapted for the World-Wide-Web in an attempt to find additional randomised controlled trials. A search strategy with the general pattern "study methodology NEAR intervention NEAR condition" for the Internet search engine AltaVista was evaluated. Measurements: Search time; recall of Internet searches for published studies; precision (proportion of webpages containing hints to relevant published and unpublished randomised clinical trials) ; number of additional unpublished or ongoing studies found on the Internet. Results: We reviewed 429 webpages in 21 hours and found hints to 16 unpublished, ongoing or recently finished trials, at least 9 were considered relevant for 4 systematic reviews. The recall of Internet searches to find references to published studies ranged between 0% and 43.6%, the precision for hints to published or unpublished studies ranged between 0% and 20.2%. Conclusion: Information on unpublished and particularly ongoing trials can be found on the Internet. A potential problem are non-peer reviewed electronic publications with questionable quality. More powerful search tools are needed. An "Open Trial Initiative" is proposed to define a syntax for publishing trials on the web and to ensure interoperability of trial registers, so that special search engines can harvest information on ongoing and completed clinical trials.