[Systematic reviews and meta-analysis].

Over the past years, systematic reviews and meta-analyses have led to significant changes in clinical medicine and health policy. To date, they can be viewed as the most objective instruments to answer clinical as well health policy questions. In addition, systematic reviews are an important tool to synthesize the enormous amount of new medical knowledge into a manageable format. Nevertheless, the methodological quality of published systematic reviews and meta-analyses varies and biased results can be misleading. Therefore, it is important for readers of systematic reviews to critically evaluate the underlying methods, to be able to assess the validity of their findings. This manuscript is part of a methods series of the Wiener Medizinische Wochenschrift. It summarizes the methodological hallmarks of systematic reviews and meta-analyses to provide readers with the methodological background necessary to critically evaluate systematic reviews and meta-analyses.