type="main" <p>This article examines the welfare impact of imperfect competition in the Medicare supplement insurance (Medigap) market. Two firms control nearly three fourths of the Medigap market, and premiums exceed claims by over 25%. I find that a low price elasticity and consumers' brand...</p>

We measure provider coverage networks for plans on the Massachusetts health insurance exchange using a two measures: consumer surplus from a hospital demand system and the fraction of population hospital admissions that would be covered by the network. The two measures are highly correlated, and...