Measuring healthy ageing: development and validation of a multidomain Healthy Ageing Index in the Korean Longitudinal...

Korea's rapidly ageing population requires a practical, policy-relevant measure of healthy ageing for population monitoring and future policy evaluation. This study developed and validated a multidomain Healthy Ageing Index aligned with the World Health Organization framework, integrating intrinsic capacity and environmental context.

Using nationally representative data from the 2021 Korean Longitudinal Healthy Ageing Study, followed by repeat-wave replication in the first follow-up, we mapped twenty-six indicators to seven domains-physical, cognitive, psychological, physiological, social, digital participation, and age-friendly environment. Indicators were normalised to a 0-1 range. Dimensionality was examined with exploratory and confirmatory factor analyses. Two composite scores were computed: an equal-weighted version and a respondent-importance-weighted version. Convergent validity was tested against activities of daily living and instrumental activities of daily living, frailty, intrinsic capacity, and health-related quality of life. Sex-stratified sensitivity analyses and an included-versus-excluded comparison were conducted to address subgroup validity and possible selection bias.

The analytic samples comprised 8444 participants at baseline and 6897 at follow-up. A seven-factor structure explained 59.6% of the variance and showed good absolute fit (goodness-of-fit index 0.97; root mean square error of approximation 0.035) with a moderate comparative fit index (0.81). Digital participation and cognition displayed the strongest correlations with the overall index (0.68 to 0.79). Higher index values were associated with fewer functional limitations, lower frailty, greater intrinsic capacity, and better quality of life, findings that were replicated at follow-up. Sex-stratified correlations were in the expected direction for both men and women. The included-versus-excluded comparison showed that respondents excluded because of missingness were generally older and in poorer health, suggesting possible selection toward a relatively healthier analytic sample.

The Healthy Ageing Index provides a multidomain measure of healthy ageing in Korea by integrating intrinsic capacity with digital and built environmental context. Its associations with function, frailty, intrinsic capacity, and quality of life support construct validity. The strong correlation of digital participation with the index likely reflects underlying socio-cognitive and functional advantages rather than an independent causal determinant. Complete-case selection and same-sample EFA/CFA warrant cautious interpretation.