Abstract
BACKGROUND: The objective assessment of major mobility disability (objective MMD) by a 400-m walk test (400 MWT) is important but not always practical. Previous research on the relationship between self-reported MMD (SR MMD) and objective MMD is sparse and limited to cross-sectional data. METHODS: We evaluated agreement between SR MMD and objective MMD using longitudinal data from the Lifestyle Interventions for Elders (LIFE) study. The SR MMD indices were defined based on having a lot of difficulty or inability to walk a quarter of a mile (SR-1/4MILE), walk several blocks (SR-BLOCKS), and climb one flight of stairs (SR-STAIRS). RESULTS: Using objective MMD as the gold standard, SR-1/4MILE and SR-BLOCKS had relatively low sensitivity (around 0.4) and high specificity (around 0.9) for prevalence. Their overall sensitivity and specificity for cumulative incident objective MMD were approximately 0.6 and 0.8, respectively. While the annual probability of staying MMD free was similar for objective MMD, SR-1/4MILE, and SR-BLOCKS (90% for all), the probability of recovering from SR MMD was higher (50%) than that of objective MMD (22%). The development of objective MMD (439 events), SR-1/4MILE (356 events), and SR-BLOCKS (379 events) had a similar trajectory over time with substantially overlapping survival curves. SR-STAIRS generally did not agree well with objective MMD. Incorporating SR-STAIRS with either SR-1/4MILE or SR-BLOCKS did not significantly improve the agreement between SR MMD and objective MMD. CONCLUSIONS: Simple SR-1/4MILE and SR-BLOCKS are reasonable candidates to define MMD if the primary outcome of interest is incident MMD.