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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

O’Malley, Jean P., MPH; O’Keeffe-Rosetti, Maureen, MS; Lowe, Robert A., MD; Angier, Heather, MPH; Gold, Rachel, PhD, MPH; Marino, Miguel, PhD; Hatch, Brigit, MD, MPH; Hoopes, Megan, MPH; Bailey, Steffani R., PhD; Heintzman, John, MD, MPH; Gallia, Charles, PhD; DeVoe, Jennifer E., MD, DPhil

doi: 10.1097/MLR.0000000000000600
Original Articles

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.

Objectives: (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.

*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


Oregon Health Authority, Portland, OR

Supported by grant R01HL107647 from the National Heart, Lung, and Blood Institute, K23DA037453 from the National Institute on Drug Abuse, K08 HS021 522 from the Agency for Healthcare Research and Quality, and the Oregon Health & Science University Department of Family Medicine.

The research presented in this paper has received Oregon Health & Science University institutional review board approval.

The authors declare no conflict of interest.

Reprints: Heather Angier, MPH, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239. E-mail:

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