Disability in activities of daily living: Patterns of change and a hierarchy of disability

Objectives. This paper examines longitudinal data over 6 years to evaluate incidence rates of disability and the pattern of dependency in activities of daily living. Methods. The Longitudinal Study of Aging (n = 5151) was used to evaluate incidence of disability in activities of daily living; biennial interview data from 1984 through 1990 were used. The median age to disability onset for individual activities was estimated from survival analysis. A prevalent ordering of incident disability was identified from patterns of disability onset within individuals. Results. The progression of incident disability among the elderly supported by longitudinal data, based on both the ordering of median ages to disability onset and patterns of incident disability, was as follows: walking, bathing, transferring, dressing, toileting, feeding. Gender differences were found in disability incidence rates. Conclusions. This study provides a mathematical picture of physical functioning as people age. These findings, based on longitudinal data, indicate a different hierarchical structure of disability than found in previous reports using cross-sectional data. Furthermore, the study documents gender differences in incident impairment, which indicate that although women outlive men, they spend more time in a disabled state.