The number of operations that surgeons have previously performed is associated with their patients' outcomes. However, this association may not be causal because previous studies have often been cross-sectional and their analyses have not considered time-varying confounding or positivity violations. Using the example of surgeons who perform coronary artery bypass grafting, we first describe (hypothetical) target trials to estimate the causal effect of the surgeons' operative volumes on patient mortality. We then demonstrate how to emulate these target trials using data from United States Medicare claims and provide effect estimates. Our target trial emulations suggest that interventions on physicians' volume of coronary artery bypass grafting operations have little effect on patient mortality. The target trial framework highlights key assumptions and draws attention to areas of bias in previous observational analyses that deviated from their implicit target trial. The principles of the presented methodology may be adapted to other scenarios of substantive interest in health services research.
Keywords: Coronary artery bypass grafting; Health services research; Inverse Probability Weighting; Marginal Structural Model; Operative volume; Target trial.
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