Abstract
BACKGROUND: Most previous studies of frailty trajectories in older adults focus on the average trajectory and ignore death. Longitudinal quantile analysis of frailty trajectories permits the definition of reference curves, and the application of mortal cohort inference provides more realistic estimates than models that ignore death. METHODS: Using data from individuals aged 65 or older (n = 25 446) from the Survey of Health, Ageing, and Retirement in Europe (SHARE) from 2004 to 2020, we derived repeated values of the Frailty Index (FI) based on the accumulation of health deficits. We applied weighted Generalized Estimating Equations to estimate the quantiles of the FI trajectory, adjusting for sample attrition due to death, sex, education, and cohort. RESULTS: The FI quantiles increased with age and progressed faster for those with the highest level of frailty (β^a0.9 = 0.0229, p < .001; β^a0.5 = 0.0067, p < .001; H0: βa0.5=βa0.9, p < .001). Education was consistently associated with a slower progression of the FI in all quantiles (β^ae0.1 = -0.0001, p < .001; β^ae0.5 =-0.0004, p < .001; β^ae0.9 = -0.0003, p < .001) but sex differences varied across the quantiles. Women with the highest level of frailty showed a slower progression of the FI than men when considering death. Finally, no cohort effects were observed for the FI progression. CONCLUSIONS: Quantile FI trajectories varied by age, sex, education, and cohort. These differences could inform the practice of interventions aimed at older adults with the highest level of frailty.