Role of Systematic Reviews and Meta-analysis in Evidence-based Medicine

The overwhelming increase in the quantity of clinical evidence has led to detachment of the evidence and practice because new evidence can be integrated into clinical practice only after it has been critically appraised and synthesized on the basis of the existing evidence. Because many clinicians lack the skills and the time for such information processing, systematic reviews and meta-analyses, their quantitative counterparts, play an important role in health care. Well performed systematic reviews provide clinically relevant information for surgeons, abrogating the need to identify, read, and evaluate many individual studies. This article reviews the basic principles of meta-analysis, discusses its potential weaknesses such as heterogeneity and publication bias, and highlights special situations when dealing with surgical trials. The practice of evidence-based surgery consists of three essential parts: the preferences, concerns, and expectations of each patient; the clinical expertise including skills, past experience, and knowledge of the surgeon; and the best research evidence that is relevant for clinical practice [1]. The challenge for a surgeon today is the last part of this definition. The traditional acquisition of knowledge from interand intraspecialty consultation during work or at a congress is limited in many ways (e.g., incomplete or biased knowledge of colleagues, uncontrolled statements without quantification, conflicts of interest). The most important source for external evidence is therefore the medical literature. In the medical literature, randomized controlled trials (RCTs) are considered a reference standard of clinical research methods owing to a number of unique characteristics that try to avoid possible biases. Surgeons, however, who try to upgrade their knowledge by reading journal articles face an enormous task. There are about 200 major surgical journals, and each journal publishes about 250 articles per year. Thus, any surgeon who wants to keep abreast of new knowledge must browse through 50,000 articles per year, which means 137 articles per day. This figure may be smaller for a highly specialized surgeon, who can carefully select his or her reading, but it still requires much more time than a busy surgeon can spare [2]. In addition to the huge volume of literature, its scattered nature poses further problems. Every time a new article appears, readers must compare this new piece of evidence with the existing external evidence to come to an overall clinical conclusion. This process of collecting and summarizing scientific information over many years requires extraordinary memory capacities that most human brains simply lack. A third problem of the surgical literature lies in the small proportion of high-quality evidence in most journals [3]. The number of surgical randomized controlled trials is still small, and case reports and series seem to be the predominant publication type. Reading surgical articles can also be trying owing to differences in study quality, such as insufficient sample size, unclear methodology, and nonclinical outcome parameters [4]. It is therefore not surprising that many surgeons subscribe to only a few selected journals. In consequence, clinicians are often unaware of important surgical innovations. On the other hand, researchers are sometimes disappointed by the small overall impact of the publication of a major trial. Here, systematic reviews are an important tool for finding important and valid studies while filtering out the large number of seriously flawed and irrelevant articles. By condensing the results of many trials, systematic reviews allow readers to obtain a valid overview on a topic with substantially less reading time in-