Market power and contract form: evidence from physician group practices.

We examine how the market power of physician groups affects the form of their contracts with health insurers. We develop a simple model of physician contracting based on 'behavioral economics' and test it with data from two sources: a survey of physician group practices in Minnesota; and the physician component of the Community Tracking Survey. In both data sets we find that increases in groups' market power are associated with proportionately more fee-for-service revenue and less revenue from capitation.