Hierarchical Structure in Activities of Daily Living and Long-Term Disability Trajectories in the Elderly Chinese Population: A 20-Year Cohort Study

Abstract Background: The global burden of disability is rising. Understanding the hierarchical structure of activities of daily living (ADL) and the disability trajectory of elderly people is pivotal to developing early interventions. Purpose: We aimed to determine the hierarchical structure of the ability to perform ADL and further describe the disability trajectory of the elderly before death. Methods: A longitudinal item response theory model (LIRT) was constructed from 28 345 elderly participants in the Chinese Longitudinal Healthy Longevity Survey, in which ADL were measured by the Katz scale for up to 20 years from 1998 to 2018, until the participants' death. The disability values estimated from the LIRT were fitted to a mixed-effects model to examine how the disability trajectories varied with different demographic characteristics. Results: The difficulty parameters showed that ADL losses began with bathing-partial (B=-1.396, SE=0.003), then toileting-partial, bathing-total, dressing-partial, transferring-partial, dressing-total, feeding-partial, continence-partial, toileting-total, feeding-total, transferring-total, and ended with continence-total (a=3.647, SE=0.013). 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, people who lived in urban areas, and those who lived without a spouse had poorer disability status. Conclusion: Losses in the ability to perform ADL have a hierarchical structure. Demographic characteristics affect disability trajectories among the elderly Chinese population.