Hospital Network Competition and Adverse Selection: Evidence from the Massachusetts Health Insurance Exchange

Health insurers increasingly compete on their covered networks of medical providers. Using data from Massachusetts’ pioneer insurance exchange, I find substantial adverse selection against plans covering the most prestigious and expensive “star” hospitals. I highlight a theoretically distinct selection channel: these plans attract consumers loyal to the star hospitals and who tend to use their high-price care when sick. Using a structural model, I show that selection creates a strong incentive to exclude star hospitals but that standard policy solutions do not improve net welfare. A key reason is the connection between selection and moral hazard in star hospital use.