title: The effect of HMOs on the inpatient utilization of medicare beneficiaries.
abstract: OBJECTIVE
  To determine the effect of joining HMOs (health maintenance organizations) on the inpatient utilization of Medicare beneficiaries.
  
  
  METHODS
  We linked enrollment data on Medicare beneficiaries to patient discharge data from the California Office of Statewide Health Planning and Development (OSHPD) for 1991-1995.
  
  
  METHODS
  A quasi-experimental design comparing inpatient utilization before and after switching from fee-for-service (FFS) to Medicare HMOs; with comparison groups of continuous FFS and HMO beneficiaries to adjust for aging and secular trends. The sample consisted of 124,111 Medicare beneficiaries who switched from FFS to HMOs in 1992 and 1993, and random samples of 108,966 continuous FFS beneficiaries and 18,276 continuous HMO enrollees yielding 1,227,105 person-year observations over five years.
  
  
  METHODS
  Total inpatient days per thousand per year.
  
  
  RESULTS
  When beneficiaries joined a group/staff HMO, their total days per year were 18 percent lower (95 percent confidence interval, 15-22 percent) than if the beneficiaries had remained in FFS. Total days per year were reduced less for beneficiaries joining an IPA (independent practice association) HMO (11 percent; 95 percent confidence interval, 4-19 percent). Medicare group/staff and IPA-model HMO enrollees had roughly 60 percent of the inpatient days per thousand beneficiaries in 1995 as did FFS beneficiaries (976 and 928 versus 1,679 days per thousand, respectively). In the group/staff model HMOs, our analysis suggests that managed care practices accounted for 214 days of this difference, and the remaining 489 days (70 percent) were due to favorable selection. In IPA HMOs, managed care practices appear to account for only 115 days, with 636 days (85 percent) due to selection.
  
  
  CONCLUSIONS
  Through the mid-nineties, Medicare HMOs in California were able to reduce inpatient utilization beyond that attributable to the high level of favorable selection, but the reduction varied by type of HMO.
authors.affiliation: RAND, 1700 Main Street, PO Box 2138, Santa Monica, CA 90407-2138, USA.
authors.forename: Nasreen
authors.initials: N
authors.lastname: Dhanani
authors.forename: June F
authors.initials: JF
authors.lastname: O'Leary
authors.forename: Emmett
authors.initials: E
authors.lastname: Keeler
authors.forename: Anil
authors.initials: A
authors.lastname: Bamezai
authors.forename: Glenn
authors.initials: G
authors.lastname: Melnick
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002140:California; D018588:Fee-for-Service Plans; D005260:Female; D006279:Health Maintenance Organizations; D006761:Hospitals / Q000706:statistics & numerical data*; D006801:Humans; D015273:Insurance Selection Bias; D007902:Length of Stay / Q000706:statistics & numerical data*; D008297:Male; D006278:Medicare; D015233:Models, Statistical; D010343:Patient Admission / Q000706:statistics & numerical data*; D012044:Regression Analysis; D014481:United States