Given a certain distribution of effect modifiers across studies, grouping of studies for the analysis has an impact on heterogeneity and inconsistency. (a) Pooled results of all trials as obtained with a pairwise meta-analysis results in great amount of heterogeneity. (b) Network meta-analysis with grouping of studies according to type of comparison (AD, AE, or AF) results in inconsistency in the absence of heterogeneity. (c) Network meta-analysis with grouping of studies by treatment class (AD and AE vs AF) results in absence of inconsistency but presence of between-study heterogeneity (across studies 1 to 4).
Jansen and Naci BMC Medicine 2013 11:159 doi:10.1186/1741-7015-11-159