Commercial Insurer Market Power and Medicaid Managed Care Networks.

This article examines the relationship between commercial insurer market power and the breadth of Medicaid managed care (MMC) physician networks. Using national enrollment and provider directory data from 2019, the study finds that insurers with greater commercial market share—defined as their share of employer-sponsored insurance and Affordable Care Act marketplace enrollment in a county—have substantially broader Medicaid physician networks. Specifically, insurers with over 30% commercial market share had Medicaid networks that were 37.3% broader than those of insurers without commercial market participation, with notable differences across primary care and several specialist categories. The findings suggest that insurers' bargaining power in commercial markets may spill over to expand Medicaid network access, potentially affecting care availability for Medicaid beneficiaries.