The impact of revision for coinsurance rate for elderly on healthcare resource utilization: a pilot study using interrupted time series analysis of employee health insurance claims data

Cost sharing, including copayment and coinsurance, is often used as a means of containing medical expenditure by reducing unnecessary or excessive use of health-care resources. Previous studies have reported the effects of reducing the coinsurance rate in Japan from 30% to 10% on demand for medical care among people aged 70 years. However, the coinsurance rate in Japan for individuals aged 70–74 years old has recently been increased from 10% to 20%. This study aimed to estimate the economic impact of coinsurance rate revision on health-care resource utilization using interrupted time-series analysis of employee health insurance claims data. I classified those who were born in FY 1944 and whose coinsurance rates decreased to 20% into the 10%-reduction group. It was found that the 10%-reduction group showed a lower increase of health-care utilization than the 20%-reduction group. However, no significant differences were observed in the overall and inpatient settings. The results of this study suggest that increasing the coinsurance rate among elderly people would reduce outpatient health-care resource utilization; however, it would not necessarily reduce overall health-care resource utilization.