Meta-analysis is the process of synthesising the results from separate, but related studies, in order to obtain an overall estimate of treatment effect. Traditionally, meta-analyses have synthesized the results from a set of trial comparisons each directly comparing the same two treatments. There are, however, potential drawbacks with such pairwise meta-analyses. In particular, it may be impossible to estimate the treatment effect of interest, or, where there is both direct and indirect evidence available, potentially important indirect information may be excluded from the analysis. Network meta-analysis is an extension of pairwise meta-analysis that derives estimates of the relative efficacy of two or more treatments from a statistical analysis of data from a set of randomized clinical trials (RCTs) that form a “connected” network of comparisons.