How Should Disability Be Measured in Older Adults? An Analysis from the Boston Rehabilitative Impairment Study of the Elderly

OBJECTIVES: To determine and compare the predictive validity and responsiveness of the Late-Life Function and Disability Instrument (LLFDI) frequency and limitation dimensions in assessing two critical dimensions of disability: frequency of and limitations in performance of major life roles. DESIGN: Secondary analysis of 2-year follow-up data from the Boston Rehabilitative Impairment Study of the Elderly. SETTING: Primary care. PARTICIPANTS: Community-dwelling older adults (≥65) (n = 430) at risk of mobility decline. MEASUREMENTS: The LLFDI frequency and limitation dimensions, self-rated health, hospitalizations, and emergency department (ED) visits over 2 years. Responsiveness measures included effect size (ES) estimates and minimal detectable change (MDC) scores. RESULTS: The LLFDI frequency dimension predicted low self-rated health (odds ratio (OR) = 0.51, P < .001), hospitalizations (OR = 0.68, P < .001), and ED visits (OR = 0.73, P = .003) over 2 years, whereas the limitation dimension did not. The absolute ES was 0.63 for the frequency dimension and 0.81 for the limitation dimension. The proportion of subjects with a decline greater than or equal to the MDC was 10.6% for the frequency dimension and 14.2% for the limitation dimension. For participants who improved greater than or equal to the MDC, the proportion was 1.7% for the frequency dimension and 15.3% for the limitation dimension. CONCLUSION: Frequency of participation in major life roles was a better predictor of adverse outcomes than perceived limitations, although limitations appeared to be more responsive to meaningful change. These results can be used to guide the selection of the most appropriate metric for measuring disability in geriatric research.