Volume 53 | Number 2 | April 2018

Abstract List

Michael R. Richards M.D., Ph.D., M.P.H., Catherine T. Smith B.S., Amy J. Graves S.M., M.P.H., Melinda B. Buntin Ph.D., Matthew J. Resnick M.D., M.P.H., M.M.H.C.


To calculate physician concentration levels for all U.S. markets using detailed data on integration and accountable care organization () participation.

Data Source

2015 &A office‐based physician survey linked to all commercial and public payer s.

Study Design

We construct three separate Herfindahl–Hirschman Index () measures and plot their distributions. We then investigate how prevailing levels of concentration change when incorporating more detailed organizational features into the measure.

Principal Findings

Horizontal and vertical integration strongly influences measures of physician concentration; however, s have limited impact overall. s are often present in competitive markets, and only in a minority of these markets do s substantively increase physician concentration.


Monitoring effects on physician competition will likely have to proceed on a case‐by‐case basis.