Evaluation of the usefulness of Internet searches to identify unpublished clinical trials for systematic reviews

Primary objective: To avoid selection and publication bias, systematic revi ewers should employ a broad range of search techniques and make efforts to locate unpublished studies. We tried to establish whether searches on the W orld Wide Web (WWW) are useful to identify additional unpublished and ongoi ng clinical trials. Research design: Search strategies of seven Cochrane systematic reviews wer e retrospectively adapted for the WWW in an attempt to find additional rand omized controlled trials. Methods and procedures: A search strategy with the general pattern 'study m ethodology NEAR intervention NEAR condition' for the Internet search engine AltaVista was evaluated by measuring search time, recall of Internet searc hes for published studies; precision (proportion of webpages containing hin ts to relevant published and unpublished randomized clinical trials); numbe r of additional unpublished or ongoing studies found on the Internet. Main outcomes and results: We reviewed 429 webpages in 21 hours and found h ints to 14 unpublished, ongoing or recently finished trials, at least 9 wer e considered relevant for 4 systematic reviews. The recall of Internet sear ches to find references to published studies ranged between 0%, and 43.6%, the precision for hints to published or unpublished studies range between 0 % and 20.2%. Conclusions: Information on unpublished and particularly ongoing trials can be found on the Internet.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.