The main aim of a Cochrane review is to provide the ‘best available’ and most up-to-date evidence on the effects of interventions for use by consumers, clinicians and policy makers to inform healthcare decisions. Since evidence on a given subject is generally dynamic and continually evolving, incorporating additional studies as they become available can change the results of a systematic review (Chalmers 1994). Therefore, systematic reviews that are not maintained run the risk of becoming out of date and even misleading. An important feature of Cochrane reviews is that review authors are committed not only to preparing systematic reviews of evidence, but also to maintaining (and updating) these reviews on a regular basis.