= Indirect treatment comparison
{title2=$\widehat\delta_{AB}=\widehat\delta_{AC}-\widehat\delta_{BC}$}
For <independent> studies comparing treatments $A$ and $B$ to common control $C$, a consistent <log odds ratio> comparison uses $\widehat\delta_{AB}=\widehat\delta_{AC}-\widehat\delta_{BC}$, with <variance> $v_{AC}+v_{BC}$. This follows from subtracting two estimates of additive effects relative to the same reference. With overlapping evidence, subtract twice their <covariance>. Causal comparability across the studies is supplied by <transitivity in network meta-analysis>, not by the <variance> calculation.
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