Systematic reviews: let's keep them trustworthy

The advent of systematic reviews is relatively new and represents an important tool to summarize the best evidence for studying the effects of healthcare interventions. Without systematic reviews, the effectiveness of therapies (or lack of benefit) can remain unrecognized for many years. The Cochrane logo (www.cochranelibrary.com) provides a good example: it shows the forest plot of a systematic review describing how corticosteroids given to women who are about to give birth prematurely can save the life of the newborn child, an important summary of the evidence available at the time. Systematic reviews as a publication type have increased over the last decade. They were initially concerned with therapeutic interventions, but there are now many more types, from ‘umbrella’ reviews (reviews of reviews) to reviews of observational studies and case reports. The methods of the review will depend on the question being asked. Systematic reviews carry an aura of infallibility but are highly dependent on the methods used and the quality of information that they summarize. A well‐performed systematic review of high‐quality randomized controlled trials (RCTs) is usually assigned to the top of the evidence pyramid for assessing the effects of interventions. However, a poorly performed systematic review that includes only a subset of all relevant evidence with little attempt to rate the quality of the included studies can produce false conclusions. The review's position in the evidence pyramid is anchored by the quality of its included studies. For example, a systematic review of case reports is likely to be misleading due to publication bias affecting the included studies, in which reports showing benefit of a new intervention are more likely to be published than those showing no benefit. Cochrane reviews are generally more methodologically rigorous than non‐Cochrane reviews in dermatology,1 but are limited to studies of interventions and diagnostic test accuracy. These are the types of reviews with the most established methods.2 The Joanna Briggs Institute has also developed methodology for qualitative systematic reviews. However, reviews of other types of questions are less well developed and authors have less guidance to ensure a high‐quality review. The BJD aims to publish only excellent systematic reviews but of any type.