[A fixed cohort study of disability trajectory of the dying elderly in China].

Objective: To explore the trajectory of disability in the dying elderly in China. Methods: Based on the activity of daily living (ADL) data from the 2002-2018 Chinese Longitudinal Healthy Longevity Survey, the longitudinal item response theory (LIRT) model was fitted with the difficulty threshold parameters to analyze the ADL loss in the elderly in China. Then, a mixed-effects model was fitted to analyze the trajectory of the disability level of the dying elderly. Results: A total of 5 817 old adults who entered the cohort in 2002 were included, in whom 41.81% were males, with a baseline age of (86.80±12.40) years and a follow-up time of 4 (3,8) years. The results of LIRT showed that the lowest difficulty threshold parameter in the basic activity of daily living (BADL) was partially disability on bathing (0.41±0.05), and the highest was entirely disability on indoor movement (6.19±0.16). In comparison, the lowest difficulty threshold parameter in instrumental activity of daily living (IADL) was partially disability on using public transportation (-3.01±0.07), and the highest was entirely disability on visiting neighbors (1.51±0.07). In the trajectory of disability, the average dependency in ADL was lower in dying men than in dying women (P<0.001), in the elderly living alone than in the elderly living with family members (P<0.001) and in the non-illiterate elderly than in the illiterate elderly (P<0.001). The estimated value of both the linear change rate and quadratic coefficient of disability level development with time were 0.231 (P<0.001) and 0.002 (P<0.001). Conclusions: In China, the development of disability in the elderly in China has its characteristics, IADL disability might occurs earlier than BADL. Among the IADL/BADL items, the disability of lower limb-based items is more prone to occur compared with upper limb-based items, and the disability of complex items is more prone to occur compared with simple items, and the growth rate of the disability trajectory also accelerates over time. It is necessary to pay attention to old women, old people living with family members, old people with low education level and old people with poor cognitive function in the disability prevention.