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Directed acyclic graphs for when both V1 and V2 directly modify the treatment effect of X on Y. Panel A is the directed acyclic graph for the full population, while Panel B is the directed acyclic graph for the trial population. Both variables now have arrows indicating a causal effect on Y, and as a result both V1 and V2 are expected to have a different association with Y before and after conditioning on study participation.
