Figure 2.

Directed acyclic graph showing the relation between placental abruption (X) and perinatal mortality (Y) with preterm delivery as the intermediary (mediating) covariate (M), US singleton births, 1995–2002. “C” is a set of confounders observed at baseline (common causes for placental abruption, preterm delivery, and perinatal mortality), and “U” is a set of unobserved confounders. We represent the relation between X and U as a dashed line because we do not consider this confounding scenario; consequently, our sensitivity analysis assumes that this pathway does not exist, and that we believe this confounding is weak in comparison.