Jill R. Horwitz (Michigan) has posted Does Nonprofit Ownership Matter?, 24 Yale. J. Reg. ___ (2007), on SSRN.  Here is the abstract:

In recent years, policymakers have increasingly questioned whether nonprofit institutions, particularly hospitals, merit tax exemption. They argue that nonprofit hospitals differ little from their for-profit counterparts in the provision of charity care and, therefore, should either lose their tax-exempt status or adhere to new, strict, and specific requirements to provide free services for the poor. In this Article, I present evidence that hospital ownership — whether it is for-profit, nonprofit, or government owned — has a significant effect on the mix of medical services it offers. Despite notoriously weak enforcement mechanisms, nonprofit hospitals act in the public interest by providing services that are unlikely to be offered by the other types of hospitals. Imposing onerous charity requirements or limiting nonprofit tax exemptions may have severe and unintended consequences for all patients, including the well-insured.