Figure 3.

DAGs of indirect Berkson’s fallacy in the association between exposure and disease in hospital-based studies. Exposure (E) does not directly lead to hospitalization (H), but via a disease (D1); (a) E causes D1, (b) E is a consequence of D1, or (c) E shares a common cause with D1. This disease is independent of the case disease (D2) in the study base, but become associated with those diseases conditional on hospitalization. Thus, in a hospital-based study, E can be spuriously associated with D2 via D1.