OBJECTIVES: To develop a cognition bolt-on version of the Japanese 5-level EQ-5D (EQ-5D-5L+C) by referring to a previously published bolt-on version, we linguistically validated a cognitive dimension and psychometrically validated the EQ-5D-5L+C.

METHODS: Following linguistic validation of the cognition dimension performed according to a standard process, psychometric validation utilized data collected from residents of six nursing homes between Oct-2021 to Jan-2022 for its main study. The EQ-5D-5L modification and its use were granted by the EuroQol group. Anonymized data of background information, EQ-5D-5L+C and EQ-5D-5L (both proxy versions responded by the nursing home staff), and Mini-Mental State Examination (MMSE) at baseline and month 3 were drawn. Validity, reliability, and sensitivity were evaluated.

RESULTS: The Japanese EQ-5D-5L+C was finalized after forward and back translations of the cognition dimension and cognitive interviews where 5 professional/family caregivers answered and understood the cognition dimension along with the Japanese EQ-5D-5L without major difficulty. Data of 254 participants was analyzed for the psychometric validation. Mean (± standard deviation) age and Barthel Index scores at baseline were 87.14±7.29 years and 52.47±30.58, respectively, with 68.9% being women and donepezil being most frequently prescribed (7.5%).No ceiling or floor effects were found in the cognition dimension. For construct validity, the strongest correlation was found between the cognition dimension and MMSE scores (r_s=-0.640). The test-retest reliability in the cognition dimension between two time points was good (k=0.644, 95% confidence interval [CI]: 0.541–0.746). Although the sensitivity to change was weak between changes in the cognition dimension and MMSE score (r_s=-0.191 [95%CI: -0.325–-0.058]), adding the cognition dimension to EQ-5D-5L benefited in capturing MMSE score changes.

CONCLUSIONS: The Japanese proxy version of EQ-5D-5L+C is a valid tool to capture health status including cognitive function in the elderly nursing home residents in Japan, with a careful consideration required to capture cognitive changes.