Time-Varying Nature of Risk Factors for the Longitudinal Development of Disability in Older Adults with Arthritis

BACKGROUND: To investigate changes over time in risk factors for the development of Activities of Daily Living (ADL) disabilities in older adults with arthritis. METHODS: The data were obtained from the Longitudinal Survey of Health and Living Status of the Elderly in Taiwan (1989–1999). The major analytic cohort comprised 977 older adults (458 men and 519 women) with arthritis and without ADL limitation at study baseline. A generalized estimating equations (GEE) model was used to analyze all temporally correlated errors, population-averaged estimates, and longitudinal relationships. RESULTS: Overall, the cumulative incidence of ADL disability in the analytic cohort was 17.4% during an observation period of 11 years. With respect to baseline risk, ADL disability was associated with older age, presence of comorbid chronic conditions, and poor self-rated health. However, the findings changed after accounting for the time-varying nature of risk factors and the temporal sequence of possible cause-and-effect relationships. In addition to the baseline predictors, a high score on the Center for Epidemiologic Studies Depression Scale, lack of regular exercise, and becoming widowed were associated with an increased risk of ADL disability and a decreased chance of recovery. CONCLUSIONS: An understanding of the time-varying nature of risk factors for the disabling process is essential for the development of effective interventions that aim to maintain functional ability and prevent limitations among older adults with arthritis.