Figure 6
Interaction plots. Interaction plots for the (X 1, X 2 ) interaction under Model 4 (no true interaction) and Model 5 (Interaction odds ratio = 2). We find that the lines for Model 4 are reasonably parallel, whereas in Model 5 they are not, indicating presence of multiplicative interaction. Note the y-axis are logit-transformed probabilities. The solid line represents the subgroup with X 2 = 0 and the dotted line represents the subgroup with X 2 = 1.