Does co-payment rate influence the relationship between monthly salary and health care service demand among the insured of health insurance societies in Japan?

The co-payment rate for health care services for insured people increased from 10% to 20% in 1997, and then to 30% in 2003 under the Employed Health Insurance System in Japan. The purpose of this study is to quantify the relationship between average monthly salary and health care service demand by different co-payment rates among the insured of health insurance societies in Japan. Data from the National Federation of Health Insurance Societies from 1996, 2002, and 2007 were analyzed. Indicators of health care service demand included case rates and number of service days per case for inpatient, outpatient, and dental services. The authors evaluated the relationship of average monthly salary with these indicators using multiple regression analyses for each of the 3 years. In the study, the average monthly salary showed a high positive correlation with outpatient and dental case rates for all 3 years. The magnitude of the relationship of average monthly salary to health care service demand was intensified as patient co-payment increased from 10% to 20%. However, it did not change when the co-payment increased from 20% to 30%. The increase in patient co-payment rate from 20% to 30% did not intensify the relationship between average monthly salary and health care service demand among the insured of health insurance societies in Japan.