(Standard) NMA

Suppose we have a set of trials comparing multiple interventions (more than two) for their efficacy/safety, forming a network of evidence. An example of such a network is depicted in the network plot in figure 1. Nodes represent interventions and edges represent direct evidence; interventions are linked with an edge, when there are studies comparing them. Intervention effects between any pair of interventions are informed both from studies directly comparing these interventions (direct evidence) and from other studies (indirect evidence), as long as there is a path one can follow from one node to the other. For example, in the network described in figure 1, there is no line/edge (direct evidence) comparing interventions ‘A+B’ and ‘A+B+C’, but one can go from ‘A+B’ to ‘A+B+C’ via usual care (UC) or another path. By synthesising both direct and indirect evidence, NMA results in more precise effect estimates and allows us to estimate the relative efficacy/safety between any pair of interventions, even of those not compared directly in a study.1–4 The main assumption made is that of transitivity, suggesting that the distribution of effect modifiers should be similar across treatment comparisons. Suppose …