Background
In this study, we analyzed the association between the score on the risk assessment scale for incident functional disability (risk score) and the cumulative medical and long-term care costs over the following three years, using the risk assessment scale for incident functional disability, which is used to predict the occurrence of requiring long-term care certification and to estimate long-term care costs in Social Impact Bond (SIB) projects and other initiatives.
Subjects and Methods
We used a comprehensive survey of people aged 65 and over who had not received a certification of longterm care need, conducted by the Japan Gerontological Evaluation Study (JAGES) in Taketoyo Town, Aichi Prefecture, in October 2016. Based on the KDB system and long-term care insurance benefit information held by the local government, we ascertained the use of medical insurance services and long-term care insurance services over a three-year period from 1 April 2017 to 31 March 2020. A total of 5,213 people (2,450 men and 2,763 women) were included. The dependent variables were the cumulative medical costs, cumulative nursing care costs, and cumulative medical and nursing care costs over the three-year period. The explanatory variables were the scores on the risk assessment scale for incident functional disability, which is scored on a scale of 0 to 48 based on 10 questions and sex and age, and the square of this score, with the higher the score, the higher the risk. The adjusted variables were the level of education, the stage of the long-term care insurance premium levy as a proxy variable for income, marital status, whether or not the person had a disease that was being treated, whether or not the person had dementia, and the follow-up days. The estimation was carried out using the ordinary least squares (OLS) method.
Results
In the analysis using a linear model, in addition to replicating the results of previous studies that showed that the cumulative nursing care costs were 9,600 yen higher for each point increase in the risk score, the cumulative medical costs were 47,300 yen higher and the cumulative medical and nursing care costs were 56,900 yen higher for each point increase in the risk score. In the analysis using a nonlinear model, a quadratic relationship was observed between the risk score and cumulative medical costs, with a peak at 44.0 points and a peak at 8.6 points. On the other hand, the relationship between the risk score and cumulative medical and nursing care costs was more appropriately linear than nonlinear.
Conclusion
The higher the risk score, the higher the cumulative medical and nursing care costs per person over the following three years, by approximately 57,000 yen. In the future, it is hoped that the risk score will be used as one of the evaluation indicators for the financial effects of medical and nursing care costs in SIB projects, etc., in addition to nursing care costs.

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