title: No significant association between anesthesia group concentration and private insurer payments in the United States.
abstract: BACKGROUND
  Markets for physician services are becoming increasingly concentrated, with many areas being dominated by a few groups. Antitrust authorities are concerned that increasing concentration will lead to inappropriately high payments for physician services from private insurers. The authors examined the association between market concentration and private insurer payments for anesthesia services.
  
  
  METHODS
  The authors obtained data on average payments from private insurers for five commonly used anesthesia Current Procedure Terminology codes for physicians located in 229 counties in the United States between 2002 and 2010. The authors calculated a measure of market concentration (the Herfindahl-Hirschman Index [HHI]) for anesthesiologists in each county using Medicare claims data. The authors then estimated the association between market concentration and private insurer payments using a difference-in-differences approach to minimize confounding.
  
  
  RESULTS
  Private insurer payments to anesthesiologists in more concentrated markets were not significantly different from payments in less concentrated markets. Compared with the 25% of counties with the least concentration (counties with an HHI in the 0th to 25th percentile), payments in counties in the 25th to 50th percentile of HHI were approximately 0.51% less (95% CI, -2.3 to 1.3%, P = 0.95), whereas payments in counties in the 50th to 75th percentile of HHI were approximately 2.8% less (95% CI, -6.7 to 1.4%, P = 0.41) and payments in counties in the 75th to 100th percentile were approximately 3.1% less (95% CI, -8.1 to 1.2%, P = 0.32).
  
  
  CONCLUSIONS
  Increasing market concentration of anesthesia groups is not associated with significantly greater payments from private insurers.
authors.affiliation: From the Department of Anesthesiology, Pain, and Perioperative Medicine, Stanford University, Stanford, California (E.C.S., A.M.); Department of Anesthesia, University of Iowa, Iowa City, Iowa (F.D.); American Society of Anesthesiologists, Washington, D.C. (T.R.M.); and Department of Health Research and Policy, Stanford University, Stanford, California (L.C.B.).
authors.forename: Eric C
authors.initials: EC
authors.lastname: Sun
authors.forename: Franklin
authors.initials: F
authors.lastname: Dexter
authors.forename: Alex
authors.initials: A
authors.lastname: Macario
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Miller
authors.forename: Laurence C
authors.initials: LC
authors.lastname: Baker
mesh_terms: D000758:Anesthesia / Q000191:economics*; D005102:Health Expenditures; D006801:Humans; D007343:Insurance Carriers / Q000191:economics*; D007348:Insurance, Health / Q000191:economics*; D011331:Private Practice / Q000191:economics*; D014481:United States