Hospital Mergers and Quality of Care: Evidence from Heart Attack Patients and Pregnancy Outcomes in Pennsylvania

We study the effects of hospital mergers on the quality of health outcomes for acute myocardial infarction (AMI) patients, patients receiving coronary artery bypass grafting (CABG) surgery and pregnant women in Pennsylvania during the period 1994-2010. We measure the quality of outcomes as risk-adjusted mortality and readmission for both AMI and CABG patients and as the incidence of preventable complications for pregnant patients. We also use total charges to measure the resources used for each patient. Using propensity scores to match hospitals involved in mergers with hospitals that have never been involved in a merger, we find that mergers that occurred in concentrated markets are associated with increased probability of in-hospital mortality and higher readmission rates for AMI patients and with increased probability of preventable complications and reduced resource utilization for pregnant patients. However, we find no evidence that mergers in more concentrated areas are associated with worse outcomes for CABG patients. Finally, we find that the effects of a merger on health outcomes may last for years.