Estimating returns to hospital volume: Evidence from advanced cancer surgery.

High-volume hospitals typically perform better than low-volume hospitals. In this paper, we study whether such patterns reflect a causal effect of case volume on patient outcomes. To this end, we exploit closures and openings of entire cancer clinics in Swedish hospitals which provides sharp and arguably exogenous variation in case volumes. Using detailed register data on more than 100,000 treatment episodes of advanced cancer surgery, our results suggest substantial positive effects of operation volume on survival. Complementary analyses point to learning-by-doing as an important explanation.