Figure 2.

Causal directed acyclic graph corresponding to target trial 2. For each surgeon, is operative volume during interval ; L_k is a vector of covariates during period (e.g., surgeon characteristics, average patient characteristics, average hospital characteristics, and mortality risk during the prior interval), with also including time-fixed surgeon and hospital covariates; is operative volume during period ; is the 90-day mortality risk of patients who underwent an operation during interval ; and U is a vector of unmeasured covariates. Directed edges between , L_k, and are omitted for simplification.