This study uses cross-sectional data from Japan's 47 prefectures covering subscribers to Japan's National Health Insurance system to analyze the effects of income and copayment levels on the utilization of medical care. Multivariate regression models were run for the years 1984 and 1989, with the utilization ratio (number of health insurance claims per 100 insurance subscribers) for total, inpatient, outpatient, and dental services as the dependent variable. Independent variables included copayment per patient day, deflated per capita income, population density, percentage of subscribers over age 65, number of beds and clinics per 1,000 persons, and number of doctors and dentists per 1,000 persons. The data were then stratified according to per capita income and percentage of insurance subscribers over the age of 65 in each prefecture. The copayment amount exhibited a small, but significant negative effect on the utilization of all medical services. Utilization of outpatient care was most sensitive to the copayment rate. The per capita income stratification models revealed the greatest copayment effect on inpatient care for the lowest income group. The results of the age stratification models support popular notions about the use of hospitals by the elderly as substitutes for elderly care facilities. The effects of copayments and income vary not only among the type of medical care (inpatient, outpatient, and dental) but also among the income and age stratifications of groups in the National Health Insurance system.
