The effect of office visit copayments on utilization in a health maintenance organization.

This study estimated the impact of a $5 copayment on office visit rates in a health maintenance organization. A quasi-experimental design was used to compare the observed changes in visit rates by state government enrollees between the year before copayments and their first year of copayments with changes between the same time periods for a control group of enrollees without copayments. Visit data for 30,415 state enrollees and 21,633 federal enrollees who were enrolled continuously for at least 12 months before and after the start of copayments were obtained from automated data systems. The introduction of a $5 copayment for office visits resulted in an estimated 10.9% decrease in primary care visits (95% confidence interval (CI): -13.4% to -8.4%) and a 3.3% drop in specialty care visits (95% CI: -15.6% to +9.0%). The effect of copayments on primary care visits by enrollees under 40 years of age was twice as large for females as for males. Copayments also had a significantly greater impact on enrollees who were high users (greater than ten primary care visits) during the year before copayments. The copayment effect was immediate and did not diminish over the 12-month study period.