The process of undertaking a systematic review and meta-analysis involves many decisions. Ideally, most of these are made while designing the protocol. It is usually necessary, however, to make further decisions in order to deal with the studies subsequently identified: few reviewers correctly anticipate all problems that arise. Many questions that arise during the review process will have obvious answers. Others will not have clear answers, and in some cases our decisions may change the whole conclusion of the review. The role of a sensitivity analysis is to determine whether the assumptions or decisions we have made do in fact have a major effect on the results of the review. You should present your investigations of the effect your assumptions had in the Results section of your review by detailing the range of treatment estimates and confidence intervals resulting from the various sensitivity analyses.