Reporting, updating, and correcting systematic reviews of the effects of health care.

The recent growth in the numbers of published systematic reviews reflects growing recognition of their importance for improving knowledge about the effects of health care. In Britain the NHS R&D Programme has established two centres to prepare systematic reviews of existing information, and the Cochrane Collaboration--an international network of individuals and institutions--evolved to produce systematic, periodically updated reviews of randomised controlled trials. The large amount of existing evidence that needs to be considered creates a problem for the reporting of systematic reviews: the need to ensure that methods and results of systematic reviews are adequately described has to be reconciled with the limited space available in printed journals. A possible solution is the use of electronic publications: reviews could be published simultaneously in a short, printed form and in a more detailed electronic form. Electronic publications also have the advantage of the ease with which reviews may be updated as new evidence becomes available or mistakes are identified.