Statistical modeling of the volume-outcome effect for carotid endarterectomy for 10 years of a statewide database

We have demonstrated a technique for rigorous statistical analysis of volume-outcome data and have found a volume effect for death after CEA in this 10-year Maryland dataset. Higher volume surgeons had lower estimated odds of death, particularly those performing four to 15 CEAs per year. These data suggest that a patient undergoing CEA by a surgeon performing an average of 16 CEAs annually has a statistically equivalent risk of death compared with one undergoing CEA by a surgeon performing any number higher than this, when controlling for hospital volume, patient comorbidity, and patient age. Hospital volume was not seen to be as significant a predictor of postoperative death in this study, with only high volume hospitals (≥130 CEAs per year) showing a statistically significant decrease in the odds ratio of death. As studies on volume-outcome relationships can have important implications for health policy and surgical training, such studies should consider non-linear effects in their modeling of procedural volume.