This is just a set of links to articles worth a look.
Dunn, Abe, and Adam Hale Shapiro, Physician Market Power and Medical-Care Expenditures. BEA working paper. April 26, 2012
We ﬁnd that physician concentration is positively and signiﬁcantly correlated with service price levels. Speciﬁcally, a 10 percent increase in the FTHHI [fixed-travel-time Herfindahl-Hirshman Index] will cause about a 1 percent increase in physician fees. Linking this ﬁnding to historical survey data discussed in Rebitzer and Vortruba  implies that physician consolidation has caused about an 8 percent increase in fees over the last two decades (1988 to 2008). We also ﬁnd that health-plan concentration is inversely correlated with service price fees. That is, insurance carriers in more concentrated health insurance markets pay lower fees to physicians.
We ﬁnd a price elasticity of supply in the range of 0.27 to 0.34 for orthopedists and 0.57 to 1.26 for cardiologists. While in most markets an upward sloping supply curve would be unsurprising, in the health service market, this means that physicians treat patients according to service price levels. In other words, a physician with a higher price-cost margin will perform more services. On the demand side, we ﬁnd a service price elasticity of demand in the range of -0.32 to -0.43 for orthopedics and -0.05 to -0.28 for cardiology patients. This ﬁnding supports prior research which suggest that patients are price sensitive, but relatively inelastic (Manning et al.  and Keeler and Rolph ).
Peter C. Smith and Andrew D. Street
Health Economics Article first published online: 11 JAN 2012 | DOI: 10.1002/hec.2793
Risk Adjustment for Dual Eligibles: Breaking New Ground in Massachusetts
Anthony Dryfus and Ellen B. Davidson. 2012.
Massachusetts Medicaid Policy Institute. January.