Abstract
<title>Abstract</title> <p>Background Population aging has increased the need for population-level measures that show how remaining life is distributed across frailty states, yet less is known about how frailty index (FI)-defined state life expectancy in Chinese adults is affected by common FI measurement choices. We examined FI-defined state life expectancy, pre-frailty transition dynamics, and cross-cohort ordering in two national Chinese studies. Methods We conducted a longitudinal multistate analysis using the China Health and Retirement Longitudinal Study (CHARLS) as the primary cohort and the Chinese Longitudinal Healthy Longevity Survey (CLHLS) as a supportive rank-order comparison cohort. Continuous-time multistate Markov models were used to estimate total and state-specific life expectancy for robust, pre-frail, and frail FI states, together with life-year gaps and one-year transition probabilities from pre-frailty at age 75 years and older. Prespecified sensitivity analyses varied the FI valid-item threshold and frailty cutoff. Results In CHARLS, 21,397 participants contributed 70,253 person-wave/death-endpoint records. Total life expectancy followed a robust > pre-frail > frail ordering; at age 80, the robust-minus-frail gap was 2.92 years (95% CI 2.39–3.81). From pre-frailty at age 75+, one-year probabilities were 10.8% (9.2–12.6) for moving to robust, 25.2% (23.0-27.5) for moving to frailty, and 3.4% (2.0-4.8) for death. The valid-item threshold of 39 and frailty cutoff of > 0.25 sensitivity rules preserved state ordering. CLHLS also preserved ordering; at age 85, robust-minus-pre-frail and pre-frail-minus-frail gaps were 0.93 (0.77–1.09) and 0.76 (0.61–0.90) years. Conclusions FI-defined state life expectancy showed stable ordering in CHARLS and supportive CLHLS rank-order consistency. These estimates provide a population-level metric for healthy-aging evaluation and cross-cohort interpretation under explicit measurement boundaries. Pre-frailty occupied a dynamic intermediate position, supporting its interpretation as a descriptive transitional life-year state.</p>