Fig. 1

The concept of network meta-analysis. Each node (circle) is considered an intervention (A, B or C), sold lines represent loops of pairwise comparison (direct evidence), and doted lines represent loops of indirect comparison (indirect evidence). Indirect comparisons can be made via deduction from the common comparator. 1.1. Indirect evidence of A versus B inferred from direct estimates of A versus C and B versus C Four studies formed the effect estimate for A-C, and 3 studies formed the effect estimate for C-B. The effect estimate of A-B was obtained from indirect evidence. 1.2. Closed network shows the a closed network meta-analysis in a hypothetical example where all interventions were compared in RCT’s, therefore; direct and indirect evidence is available for all comparisons