Content area
Abstract
A distinguishing feature of an updated systematic review from a new review is that during updating the originally formulated protocol (eg, eligibility criteria, search strategy) is retained, and sometimes extended, to accommodate newly identified evidence (eg, new treatment type, diagnostic method, outcome, different population). Apart from inconsistent use of what constitutes an update, there are other challenging issues related to updating-eg, it is not clear when to update any given systematic review.8,9 Updating that is too freguent when the pace of reported research is slow might be unnecessary and will probably result in wasted resources, whereas low updating freguency in a fast-developing specialty could render the results of systematic reviews outdated, misleading, or both.8-10 A systematic review summarising methods to indicate when and how to update systematic reviews would probably clarify any uncertainty and also highlight existing gaps in the evidence.