The Cochrane Collaboration is an international organisation that aims to help people to make well informed decisions about health by preparing, maintaining, and ensuring the accessibility of systematic reviews of the benefits and risks of health care interventions. Systematic reviews differ considerably from conventional reviews in that they are based on a scientific process designed to minimise bias. The importance of reviews to inform busy clinicians is obvious as we are now swamped by a huge body of primary medical literature and all of us struggle to keep up to date even with our specialty areas of clinical or scientific interest. Unfortunately, all too often we are ill served by conventional reviews whether published in books or in journals: they are frequently out of date at the time of publication if the topic is progressing rapidly; different “experts” can reach entirely different conclusions after reviewing the same topic as readers; we are usually not informed how the reviewer chose to select certain references and ignore others as a consequence; we cannot be sure if the review can be trusted or not.

The systematic review, in contrast, is based on an explicit and rigorous process that includes: a clear description of the objectives, explicit criteria for including studies an attempt to identify all relevant studies, whether published or not, explicit description of why apparently relevant studies have not been considered, extraction of data, pooling of data from similar studies (meta-analysis), …