Commercial Insurer Market Power and Medicaid Managed Care Networks.

Over 70% of Medicaid beneficiaries are enrolled in Medicaid managed care (MMC). MMC provider networks therefore represent a critical determinant of access to the Medicaid program. Many MMC insurers also participate in commercial insurance markets where prices are high, and some insurers exercise considerable market power. In this paper, we examined the relationship between commercial insurer market power and MMC physician network breadth using linked national enrollment data and provider directory data. Insurers with more commercial market power had broader Medicaid physician networks. Insurers with over 30% market share had 37.3% broader Medicaid networks than insurers in the same county that had no commercial market share. These differences were driven by greater breadth among primary care providers, as well as other specialists including OB/GYNs, surgeons, neurologists, and cardiologists. Commercial insurance market power may have spillovers on access to care for MMC beneficiaries.