Responsiveness of the index of mobility limitation: comparison with gait speed alone in the longitudinal aging study amsterdam.

BACKGROUND Interpreting self-reported disability differences between diverse older populations is complicated by differences in attitudes and environment. We have previously reported on the index of mobility-related limitation tests (MOBLI), and shown that it predicts mortality over 4 years. In this article, we examine whether the index is responsive to changes in self-reported mobility disability. METHODS Data on gait speed, time to complete 5 chair stands, and peak expiratory flow rate, with self-reported difficulty walking for 5 minutes, were available from the baseline and two 3-year follow-ups in the Longitudinal Aging Study Amsterdam. Analysis used data on changes in the index (or walking speed alone) and corresponding change over 3 years in self-reported difficulty or inability with a medium-distance walk. RESULTS During all follow-ups, groups reporting deterioration in functioning had relatively larger changes in gait speed and MOBLI score than did the "no deterioration" groups. In comparative analyses of responsiveness, the MOBLI score had a larger responsiveness index, higher odds ratios, and larger receiving operating characteristic area than gait speed alone. CONCLUSIONS The MOBLI index of mobility-related physical limitation tests is responsive to changes in self-reported mobility disability over two 3-year periods, and performs better than gait speed alone. This property is strongly supportive of its validity for epidemiological comparison of older populations across countries or over longer periods of time.