"Conflicting theories of the nonprofit firm have existed for several decades yet empirical research has not resolved these debates, partly because the theories are not easily testable but also because empirical research generally considers organizations in isolation rather than in markets. Here we examine three types of hospitals -- nonprofit, for-profit, and government -- and their spillover effects. We look at the effect of for-profit ownership share within markets in two ways, on the provision of medical services and on operating margins at the three types of hospitals. We find that nonprofit hospitals' medical service provision systematically varies by market mix. We find no significant effect of for-profit market share on the operating margins of nonprofit hospitals. These results fit best with theories in which hospitals maximize their own output"--National Bureau of Economic Research web site.