Figure 2.

Causal directed acyclic graphs for linear data-generating models with two-sided exposure-to-outcome sibling spillover. Subscripts i and j denote family and sibling, respectively. T_ij is the exposure, Y_ij is the outcome, D_i is the gain-score, and U_i is an unobserved family-level confounder. Greek letters denote effects. (2A) does not have exposure-to-exposure spillover, whereas (2B) and (2C) have exposure-to-exposure spillover. The gain-score method identifies the differences between the spillover effects θ (T_i1 → Y_i2) and κ (T_i2 → Y_i1) in all three models.