Short-term change in physical function and disability: the Women's Health and Aging Study.

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Although measures of physical function are predictive of future disability, little is known about the short-term impact of changes in physical function on disability. Data from 93 of the 102 women who participated in the Weekly Substudy of the Women's Health and Aging Study (WHAS) were used to explore the association of changes in physical function with disability. The WHAS Substudy included 24 weekly assessments of three standard performance tests and self-reported disability in activities of daily living (ADLs) and basic mobility. Using random-effects models, we found small but significant (ps <.01) changes in ADL and mobility disability during weekly follow-up. Baseline performance scores were significantly associated with both ADL and mobility disability (ps <.001), accounting for 27% and 36% of the between-person variability in each type of disability, respectively. After adjustment for baseline scores, change in performance scores was significantly associated with ADL disability (beta = 0.08, p <.01) and mobility disability (beta = 0.12, p <.001), but accounted only for a small proportion (<10%) of the variability in the rate of change in disability outcomes. There was no evidence for an additional effect on either type of disability because of having a single episode of a higher or lower than usual performance score, or because of periods of at least 4 consecutive higher or lower than usual performance test scores. Basic physical functions account for a substantial proportion of the heterogeneity in ADL and mobility disability among older disabled women, but have a relatively small impact on short-term changes in either type of disability. Effective prevention of disability may require attention to a wider array of risk factors than just limitations in basic physical functions.