Monitoring local impacts of Medicaid expansion on primary care provider capacity: A case study from King County, Washington

We sought to assess capacity of primary care providers (PCPs) to accept new adult Medicaid patients in King County, Washington, following the Affordable Care Act’s Medicaid expansion. We extracted PCP contact information from online directories and conducted three "mystery shopper surveys," one pre- and two post-Medicaid expansion. Interviewers posed as new patients and asked about appointment wait times and whether PCPs were accepting new adult Medicaid patients. The percentage of PCPs accepting new adult Medicaid patients declined during the first 15 months post-Medicaid expansion, appointment wait times did not change significantly and we identified widespread inaccuracies in online provider directories.