biostudies-literatureUnknown53(2)Richards MR<h4>Objective</h4>To calculate physician concentration levels for all U.S. markets using detailed data on integration and accountable care organization (ACO) participation.<h4>Data source</h4>2015 SK&A office-based physician survey linked to all commercial and public payer ACOs.<h4>Study design</h4>We construct three separate Herfindahl-Hirschman Index (HHI) measures and plot their distributions. We then investigate how prevailing levels of concentration change when incorporating more detailed organizational features into the HHI measure.<h4>Principal findings</h4>Horizontal and vertical integration strongly influences measures of physician concentration; however, ACOs have limited impact overall. ACOs are often present in competitive markets, and only in a minority of these markets do ACOHealth services research1272-1285https://www.ebi.ac.uk/biostudies/studies/S-EPMC5867079biostudies-literaturePhysician Competition in the Era of Accountable Care Organizations.PMC5867079Buntin MBResnick MJRichards MRSmith CTGraves AJfalsePhysician Competition in the Era of Accountable Care Organizations.<h4>Objective</h4>To calculate physician concentration levels for all U.S. markets using detailed data on integration and accountable care organization (ACO) participation.<h4>Data source</h4>2015 SK&A office-based physician survey linked to all commercial and public payer ACOs.<h4>Study design</h4>We construct three separate Herfindahl-Hirschman Index (HHI) measures and plot their distributions. We then investigate how prevailing levels of concentration change when incorporating more detailed organizational features into the HHI measure.<h4>Principal findings</h4>Horizontal and vertical integration strongly influences measures of physician concentration; however, ACOs have limited impact overall. ACOs are often present in competitive markets, and only in a minority of these markets do ACO2018-01-01T00:00:00Z2018 Apr2025-04-04T14:49:10.166Z2019-08-04T08:22:02ZS-EPMC58670792834525610.1111/1475-6773.12690