Predictive validity of the modified Kihon Checklist for the incidence of functional disability among older people: A 3‐year cohort study from the JAGES

AIM: The original Kihon Checklist, validated to predict the incidence of functional disability, has been modified to capture both functional ability (can/cannot) and performing state (do/do not). However, the predictive validity of the modified Kihon Checklist remains unverified. Therefore, this study intends to verify the predictive validity of the modified Kihon Checklist and to clarify whether predictive discrimination differs between the classification method of functional ability and performing state. METHODS: The participants comprised 67 398 older people who responded to the Japan Gerontological Evaluation Study (2016). They were followed for 3.1 years on average. Cox's proportional hazards model with incidence of functional disability as the endpoint was used to calculate the hazard ratio, adjusted for sex and age. The independent variables were judged by two classification methods, functional ability and performing state, using nine indicators based on the modified Kihon Checklist. Additionally, we examined whether the two classification methods produced different C‐index estimates. RESULTS: Incidence of functional disability occurred in 6232 participants (9.2%). The adjusted hazard ratio of those to whom the nine indicators applied was significantly higher than that of those to whom they did not. The range of the hazard ratio was 1.50–3.82 for both classification methods. The C‐index was slightly higher when the classification was based on performing state than when it was based on on functional ability. CONCLUSIONS: Although predictive discrimination was slightly higher for the performing state than for functional ability, the predictive validity of the modified Kihon Checklist was confirmed for both. Geriatr Gerontol Int 2022; 22: 667–674.