Figure 1.

Directed acyclic graph of body mass index, other time‐varying covariates, and atrial fibrillation. The directed acyclic graph displays repeated measures at years k−1 and k. BMI _k denotes the exposure, body mass index (BMI), at year k. L_k denotes confounders at year k (eg, systolic blood pressure). AF denotes the outcome, new‐onset atrial fibrillation (AF). Arrows indicate associations (eg, the association of body mass index [BMI] and incident AF). Adjustment for intermediate variables L_k (red) in a Cox model will block the path between BMI _k−1 and AF (green), which prevents us from observing the full association. However, g‐methods can accommodate this scenario. If BMI _k−1 did not cause AF through L_k (the green arrows were not present), then L_k would not be an intermediate variable and adjustment for L_k would not block the association of BMI _k−1 and AF.