Hierarchical structure in the activities of daily living and trajectories of disability prior to death in elderly Chinese individuals

BACKGROUND: The global burden of disability continues to increase. Understanding the hierarchical structure of activities of daily living (ADL) and the trajectories of disability of elderly individuals is pivotal to developing early interventions. PURPOSE: To determine the hierarchical structure of the ability of Chinese elderly individuals to perform ADL and further describe the trajectories of disability prior to death. METHODS: Longitudinal item response theory model (LIRT) was constructed for 28,345 elderly participants in the Chinese Longitudinal Healthy Longevity Survey, in which ADL were measured using the Katz scale from 1998 to 2018, until the participants’ death. Two difficulty parameters (κ(−)partial and κ(−)total) were used in the LIRT defining the thresholds for hierarchical structure in ADL (κ(−)partial: no limitation to partial limitation, κ(−)total: partial limitation to totally limited). Disability values estimated from the LIRT were fitted to a mixed-effects model to examine the manner in which the trajectories of disability varied with different subject characteristics. RESULTS: The findings confirmed the earliest loss in the capability to perform ADL (bathing(κ(-partial) = − 1.396), toileting(κ(-partial) = − 0.904)) at the level of partial limitation, with an overlap of partial and totally limited (total bathing, partial dressing, partial transferring, total dressing, partial feeding, partial continence), and finally a total loss of capability for toileting, feeding, transferring, and continence (κ(-total) = 3.647). Disability trajectories varied with sex (β = 0.041, SE = 0.001), place of residence (β = 0.010, SE = 0.001), and marital status (β = 0.144, SE = 0.001). Females, individuals living in urban areas, and those who lived without a spouse had a poorer disability status. CONCLUSION: The loss in the ability to perform ADL has a hierarchical structure. Subject characteristics affect trajectories of disability in the elderly Chinese population. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12877-021-02460-y.