Can the Health Insurance Reforms stop an increase in medical costs of middle- and old-aged persons in Japan?

Using two-period panel data from the Nippon Life Insurance Research Institute, this paper tests the hypothesis that an increase in the self-pay ratio of medical expenditures associated with the Japanese health insurance reforms of April 2003 reduced individual medical costs. We find that the increase in the self-pay ratio of medical expenditures has a trivial effect on household medical expenses, implying that a decrease in the quantity demanded for medical services offsets the increase in medical costs. However, according to quantile regression estimates, an increase in the self-pay ratio of medical expenditures has a significantly positive effect on the share of medical costs for relatively high quantile values. This provides corroborating evidence that an increase in the self-pay ratio cannot cut the demand for medical services relatively more for those bearing a higher share of medical costs in household expenditure. An additional finding is that medical services are a necessity good, particularly for those with a relatively high share of medical costs in household expenditure.