Figure 1
From: A counterfactual approach to bias and effect modification in terms of response types
A causal diagram depicting a hypothetical example. E, D, C, and S denote exposure, disease, confounder, and selection variable, respectively. C may act as a direct effect modifier simultaneously. In this paper, S is assumed not to be influenced directly by C (i.e., the dashed arrow is absent). The present discussion, however, can be readily extended to the situations in which one assumes that the dashed arrow is present.