Learning by doing, scale effects, or neither? Cardiac surgeons after residency

Objective. To examine impacts of operating surgeon scale and cumulative experience on postoperative outcomes for patients treated with coronary artery bypass grafts (CABG) by "new" surgeons. Pooled linear, fixed effects panel, and instrumented regressions were estimated. Data Sources. The administrative data included comorbidities, procedures, and outcomes for 19,978 adult CABG patients in Florida in 1998-2006, and public data on 57 cardiac surgeons who completed residencies after 1997. Study Design. Analysis was at the patient level. Controls for risk, hospital scale and scope, and operating surgeon characteristics were made. Patient choice model instruments were constructed. Experience was estimated allowing for "forgetting" effects. Principal Findings. Panel regressions with surgeon fixed effects showed neither surgeon scale nor cumulative volumes significantly impacted mortality nor consistently impacted morbidity. Estimation of "forgetting" suggests that almost all prior experience is depreciated from one quarter to the next. Instruments were strong, but exogeneity of volume was not rejected. Conclusions. In postresidency surgeons, no persuasive evidence is found for learning by doing, scale, or selection effects. More research is needed to support the cautious view that, for these "new" cardiac surgeons, patient volume could be redistributed based on realized outcomes without disruption.