Meta-analysis allows the quantitative combination of results of multiple studies that address similar research questions. Traditional meta-analysis of studies involving a direct comparison of two treatment alternatives can be applied to estimate the overall relative efficacy of these two treatment alternatives. All treatment options relevant to practical treatment decisions are, however, not always compared directly against each other in clinical studies, but indirect comparison via a common comparator may be possible. To use all relevant evidence from both direct and indirect comparisons of treatment options, advanced methods of meta-analysis have been developed. These so-called network meta-analyses extend the traditional meta-analysis to cases where a network of studies enables different pair-wise direct and indirect comparisons between multiple treatment alternatives, thereby forming a network of relevant evidence.