Title: The changing effect of hmo market structure
Description: "We analyze the role of three aspects of HMO market structure -- HMO penetration, HMO plan concentration, and HMO for-profit share on explaining hospital cost and revenue growth during the HMO expansion period (1994-1999) and backlash period (2000-2005).  We find that HMO penetration effects differ over time: a 10 percentage point increase in HMO enrollment leads to 2.5 percent reduction in cost and revenues in the expansion period but only 0.4-1 percent reduction in the backlash period.  Furthermore, this HMO backlash effect can be attributed to HMO dis-enrollment as well as the changing nature of HMO product.  We find that revenue increases at a slower rate (by about 5 percent) in markets with relatively concentrated HMO markets power and more competitive hospital markets.  Finally, increased for-profit HMO presence is associated with smaller cost and revenue growth, and the effect differs between low and high penetration markets"--National Bureau of Economic Research web site.