EFFECT OF AGE AND SEVERITY OF DISABILITY ON SHORT-TERM VARIATION IN WALKING SPEED - THE WOMENS HEALTH AND AGING STUDY

Standardized objective measures of human performance have been introdu ced in clinical and epidemiologic studies of older populations. Reliab ility of these measures has usually been estimated by comparing two me asures obtained in the same person. However, no information is availab le on variability of multiple measures collected serially over short t ime intervals. This study uses data from the Weekly Disability Study, a component of the Women's Health and Aging Study, to describe fluctua tions in physical performance over multiple, consecutive time interval s. Walking speed was measured weekly over a 6 month period in 99 older women affected by mild to severe disability. Overall, 2120 observatio ns were explored using techniques developed for the analysis of repeat ed measures. Results showed that the correlations between observations in the same person were inversely related to their separation in time . The decay in the autocorrelation function was steeper in the least d isabled. However, even with 20-week separations in assessments, correl ations remained above 0.6 in all age and severity of disability subgro ups. Changes over time in performance differed somewhat between disabi lity subgroups, but the relative performance across subgroups remained stable over the entire course of the study. A clear learning effect w as found only in those in the middle disability subgroup. Results supp ort the utilization of repeated measures of physical performance in re search that evaluates older persons over time.