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 six-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 six-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.