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N Engl J Med. 1996 Mar 7;334(10):635-41.

Effect of a copayment on use of the emergency department in a health maintenance organization.

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Division of Research, Permanente Medical Group, Kaiser Permanente Medical Care Program, Oakland, CA 94611, USA.



Use of the emergency department for nonemergency care is frequent and costly. We studied the effect of a copayment on emergency department use in a group-model health maintenance organization (HMO).


We examined the use of the emergency department in 1992 and 1993 by 30,276 subjects who ranged in age from 1 to 63 years at the start of the study and belonged to the Kaiser Permanente HMO in northern California. We assessed their use of various HMO services and their clinical outcomes before and after the introduction of a copayment of $25 to $35 for using the emergency department. This copayment group was compared with two randomly selected control groups not affected by the copayment. One control group, with 60,408 members, was matched for age, sex, and area of residence to the copayment group. The second, with 37,539 members, was matched for these factors and also for the type of employer.


After adjustment for age, sex, socioeconomic status, and use of the emergency department in 1992, the decline in the number of visits in 1993 was 14.6 percentage points greater in the copayment group than in either control group (P<0.001 for each comparison). Visits for urgent care did not increase among subjects in any stratum defined by age and sex, and neither did the number of outpatient visits by adults and children. The decline in emergency visits for presenting conditions classified as "always an emergency" was small and not significant. For conditions classified as "often an emergency". "sometimes not an emergency", or "often not an emergency", the declines in the use of the emergency department were larger and statistically significant, and they increased with decreasing severity of the presenting condition. Although our ability to detect any adverse effects of the copayment was limited, there was no suggestion of excess adverse events in the copayment group, such as increases in mortality or in the number of potentially avoidable hospitalizations.


Among members of an HMO, the introduction of a small copayment for the use of the emergency department was associated with a decline of about 15 percent in the use of that department, mostly among patients with conditions considered likely not to present an emergency.

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