title: Health Care Utilization Rates After Oregon's 2008 Medicaid Expansion: Within-Group and Between-Group Differences Over Time Among New, Returning, and Continuously Insured Enrollees.
abstract: BACKGROUND
  Although past research demonstrated that Medicaid expansions were associated with increased emergency department (ED) and primary care (PC) utilization, little is known about how long this increased utilization persists or whether postcoverage utilization is affected by prior insurance status.
  
  
  OBJECTIVE
  (1) To assess changes in ED, PC, mental and behavioral health care, and specialist care visit rates among individuals gaining Medicaid over 24 months postinsurance gain; and (2) to evaluate the association of previous insurance with utilization.
  
  
  METHODS
  Using claims data, we conducted a retrospective cohort analysis of adults insured for 24 months following Oregon's 2008 Medicaid expansion. Utilization rates among 1124 new and 1587 returning enrollees were compared with those among 5126 enrollees with continuous Medicaid coverage (≥1 y preexpansion). Visit rates were adjusted for propensity score classes and geographic region.
  
  
  RESULTS
  PC visit rates in both newly and returning insured individuals significantly exceeded those in the continuously insured in months 4 through 12, but were not significantly elevated in the second year. In contrast, ED utilization rates were significantly higher in returning insured compared with newly or continuously insured individuals and remained elevated over time. New visits to PC and specialist care were higher among those who gained Medicaid compared with the continuously insured throughout the study period.
  
  
  CONCLUSIONS
  Predicting the effect of insurance expansion on health care utilization should account for the prior coverage history of new enrollees. In addition, utilization of outpatient services changes with time after insurance, so expansion evaluations should allow for rate stabilization.
authors.affiliation: *Department of Family Medicine, Oregon Health & Science University †Kaiser Permanente, Center for Health Research ‡Department of Emergency Medicine and Department of Medical Informatics and Clinical Epidemiology, Oregon Health & Science University §OCHIN Inc. ¶Oregon Health Authority, Portland, OR.
authors.forename: Jean P
authors.initials: JP
authors.lastname: O'Malley
authors.forename: Maureen
authors.initials: M
authors.lastname: O'Keeffe-Rosetti
authors.forename: Robert A
authors.initials: RA
authors.lastname: Lowe
authors.forename: Heather
authors.initials: H
authors.lastname: Angier
authors.forename: Rachel
authors.initials: R
authors.lastname: Gold
authors.forename: Miguel
authors.initials: M
authors.lastname: Marino
authors.forename: Brigit
authors.initials: B
authors.lastname: Hatch
authors.forename: Megan
authors.initials: M
authors.lastname: Hoopes
authors.forename: Steffani R
authors.initials: SR
authors.lastname: Bailey
authors.forename: John
authors.initials: J
authors.lastname: Heintzman
authors.forename: Charles
authors.initials: C
authors.lastname: Gallia
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: DeVoe
mesh_terms: D000293:Adolescent; D000328:Adult; D003695:Delivery of Health Care / Q000706:statistics & numerical data*; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D019458:Insurance Coverage / Q000706:statistics & numerical data*; D007348:Insurance, Health / Q000706:statistics & numerical data; D008297:Male; D008484:Medicaid / Q000706:statistics & numerical data*; D008605:Mental Health Services / Q000706:statistics & numerical data; D008875:Middle Aged; D009922:Oregon; D058991:Patient Protection and Affordable Care Act; D011320:Primary Health Care / Q000706:statistics & numerical data; D012189:Retrospective Studies; D014481:United States; D055815:Young Adult