Psychometric performance of the EQ-HWB-25 and EQ-HWB-9 in Japan: evidence from a large web-based survey of multimorbidity and depression

Background The EQ-HWB was developed to capture broader aspects of wellbeing beyond traditional health-related quality of life. However, empirical evidence from non-European populations remains limited. This study evaluated the psychometric performance of the EQ-HWB-9 utility index and the EQ-HWB-25 profile measure in a large sample of the Japanese general population, with a focus on multimorbidity and depression. Methods We analysed data from a nationwide web-based cross-sectional survey (n = 5,177). The EQ-HWB-9 utility and EQ-HWB-25 composite scores were examined across levels of multimorbidity and depression. Known-group validity was assessed via group comparisons. Multivariable ordinary least squares regression with HC3 robust standard errors was used to estimate adjusted associations between the selected conditions and the EQ-HWB-9 utility. Results The EQ-HWB-9 utility scores decreased monotonically with increasing number of comorbid conditions. The respondents reporting depression had substantially lower EQ-HWB-9 utility scores (β = -0.124 (95% CI − 0.148–−0.101)) and markedly lower standardized EQ-HWB-25 composite scores. In multivariable models adjusted for age, sex, and multimorbidity, depression, arthritis, and lower back pain were independently associated with lower EQ-HWB-9 utility scores. The EQ-HWB-25 provides complementary descriptive information, highlighting multidimensional wellbeing deficits associated with depression. Conclusions These findings support the construct validity and known-group validity of the EQ-HWB in Japan. The EQ-HWB-9 captured both the cumulative multimorbidity burden and condition-specific impacts on wellbeing, particularly for depression, whereas the EQ-HWB-25 offered broader profile-level insights. The EQ-HWB framework may be especially valuable for wellbeing assessment and economic evaluation in populations with a high prevalence of multimorbidity and depression.