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Health Serv Res. 2006 Oct;41(5):1801-20.

Cost-sharing for emergency care and unfavorable clinical events: findings from the safety and financial ramifications of ED copayments study.

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  • 1Kaiser Permanente-Division of Research, 2000 Broadway, 3rd Floor, Oakland, CA 94612, USA.



To evaluate the effect of emergency department (ED) copayment levels on ED use and unfavorable clinical events. Data Source/Study Setting. Kaiser Permanente-Northern California (KPNC), a prepaid integrated delivery system.


In a quasi-experimental longitudinal study with concurrent controls, we estimated rates of ED visits, hospitalizations, ICU admissions, and deaths associated with higher ED copayments relative to no copayment, using Poisson random effects and proportional hazard models, controlling for patient characteristics. The study period began in January 1999; more than half of the population experienced an employer-chosen increase in their ED copayment in January 2000.


Using KPNC automated databases, the 2000 U.S. Census, and California state death certificates, we collected data on ED visits and unfavorable clinical events over a 36-month period (January 1999 through December 2001) among 2,257,445 commercially insured and 261,091 Medicare insured health system members.


Among commercially insured subjects, ED visits decreased 12 percent with the $20-35 copayment (95 percent confidence interval [CI]: 11-13 percent), and 23 percent with the $50-100 copayment (95 percent CI: 23-24 percent) compared with no copayment. Hospitalizations, ICU admissions, and deaths did not increase with copayments. Hospitalizations decreased 4 percent (95 percent CI: 2-6 percent) and 10 percent (95 percent CI: 7-13 percent) with ED copayments of $20-35 and $50-100, respectively, compared with no copayment. Among Medicare subjects, ED visits decreased by 4 percent (95 percent CI: 3-6 percent) with the $20-50 copayments compared with no copayment; unfavorable clinical events did not increase with copayments, e.g., hospitalizations were unchanged (95 percent CI: -3 percent to +2 percent) with $20-50 ED copayments compared with no copayment.


Relatively modest levels of patient cost-sharing for ED care decreased ED visit rates without increasing the rate of unfavorable clinical events.

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