Development of a Healthy Aging Index and analysis of healthy aging trajectories over a 6-year period using the Korean Frailty and Aging Cohort Study

BACKGROUND AND OBJECTIVES: Measurements and data on older adults are instrumental in our understanding of healthy aging (HA). No universally agreed-upon definition and heterogeneity in the operationalization of HA have necessitated the development of better HA measures. This study aimed to develop a Healthy Aging Index (HAI) based on a multidimensional item response theory (MIRT) framework and explore patterns of HA trajectories over a 6-year period with adverse health outcomes as distal outcomes. RESEARCH DESIGN AND METHODS: Using longitudinal data (baseline to Wave 4, n = 2,986) from the Korean Frailty and Aging Cohort Study, factor analyses and a bifactor MIRT model were used to evaluate the psychometric properties. Heterogeneity in HA trajectories, with mortality and frailty as distal outcomes, was investigated using a growth-mixture model. RESULTS: The 25-item multidimensional HAI demonstrated an excellent model fit (RMSEA = 0.023, TLI = 0.979, CFI = 0.983). We identified four subgroups that exhibited similar HA trajectory patterns. Notably, compared with those in the high-stable group (57.6%), the moderate-stable (29.7%) and low-declining (4%) groups were associated with an increased risk of mortality (Odds Ratios [OR] = 2.60 and 4.55) and frailty (OR = 6.41 and 40.00) at Wave 4. The high decliners (8.7%) were more likely to be frail and exhibit worse physical function than the high-stable group over the 6-year follow-up period. DISCUSSION AND IMPLICATIONS: A multidimensional measure of HA may help identify older adults who are at risk of early mortality and frailty.