Few methodological studies have been conducted to inform decisions about how and when to update systematic reviews (Moher 2008), however this is a rapidly evolving area and the guidance contained in this chapter will be regularly updated in line with new knowledge from methodological research. An update to a Cochrane review should usually occur every two years and must involve a search for new studies. If new studies are identified, they must be assessed for inclusion and, if eligible, incorporated into the review. While preparing an update to a review, additional issues may be considered, for example:
Any need for a change in research question and selection criteria of the review: e.g. addition of a new outcome or comparison, adding a newly specified subgroup analysis following improved methods for categorizing the condition;
Change to methodology: e.g. inclusion of ‘Risk of bias’ assessment of currently-included studies (Chapter 8) or the addition of a ‘Summary of findings’ table (Chapter 11).