Primary objective: 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and publication bias, systematic reviewers should employ a broad range of search techniques and make efforts to locate unpublished studies. We tried to establish whether searches on the World Wide Web (WWW) are useful to identify additional unpublished and ongoing clinical trials.
Research design: Search strategies seven Cochrane systematic reviews were retrospectively adapted for the WWW in an attempt to find additional randomized controlled trials.
Methods and procedures: A search strategy with the general pattern 'study methodology NEAR intervention NEAR condition' for the Internet search engine AltaVista was evaluated by measuring search time, recall of Internet searches for published studies; precision (proportion of webpages containing hints to relevant published and unpublished randomized clinical trials); number of additional unpublished or ongoing studies found on the Internet.
Main outcomes and results: We reviewed 429 webpages in 21 hours and found hints to 14 unpublished, ongoing or recently finished trials, at least 9 were considered relevant for 4 systematic reviews.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searches to find references to published studies ranged between 0% and 43.6%, the precision for hints to published or unpublished studies range between 0% and 20.2%.
Conclusions: Information on unpublished and particularly ongoing trials can be found on the Internet. A potential problem is the appraisal of 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 complete clinical trials.