Systematic reviews and meta-analyses: black boxes of medical literature?

Essentially, a systematic review uses systematic and explicit methods to identify, select and critically appraise relevant research to answer a clearly formulated question. It collects and analyses data from the studies that are included in the review [1]. A meta-analysis aims to combine the quantitative results of these studies by statistical methods. Its purpose is to provide a summarized and thereby more precise effect of the results. Thus, a good systematic review is essential for a good meta-analysis [2]. That sounds quite dry. But why do we consider systematic reviews and meta-analyses that important? Because they matter! Meta-analyses and systematic reviews are a pivotal foundation for evidenced-based decision-making on diagnostic or therapeutic procedures. Physicians rely on this comprehensive knowledge and trust that they do the best possible for the patient by observing the messages. In addition, many clinical guidelines are based on systematic reviews and meta-analyses. This is the reason why our journal is committed to highest quality of this publication type, too. Further, systematic reviews and meta-analyses are valuable tools for health authorities, insurance providers and other public institutions to manage and to advance public health. However, systematic reviews and meta-analyses serve also other purposes. Knowledge of the relevant publications helps to avoid unnecessary clinical trials, when the outcome is already clear from cumulated data. ‘Unnecessary’ applies to the risk for participants, who are denied the best treatment, as well as to spending of manifold resources. Furthermore, it is not consistent with good scientific and clinical practice to ignore results of previous research. Internationally recognized guidelines for set-up and reporting of clinical trials, the SPIRIT and CONSORT Statements [3, 4], request accounting for the current knowledge, the evidence. This includes checking for up-to-date systematic reviews and meta-analyses. A systematic review requires five steps: