BACKGROUND: The Late-Life Function and Disability Instrument (LLFDI) is a well-validated and frequently used patient-reported outcome for older adults. The aim of this study was to estimate the minimal clinically important difference (MCID) of the LLFDI-Function Component (LLFDI-FC) and its subscales among community-dwelling older adults with mobility limitations.
METHODS: We performed a secondary analysis of the Boston Rehabilitative Impairment Study of the Elderly, a longitudinal cohort study of older adults with mobility limitations residing in the community. The MCID for each LLFDI-FC scale over 1 year of follow-up was estimated using both anchor- and distribution-based methods, including mean change scores on a patient-reported global rating of change in function scale, the standard error of measurement (SEM), and the minimal detectable change with 90% confidence (MDC90).
RESULTS: Data from 320 older adults were used in the analysis (mean age 76 years, 69% female, mean of four chronic conditions). Meaningful change estimates for "small change" based on the global rating of change and SEM were 2, 3, 4, and 4 points for the LLFDI-FC overall function scale and basic lower-extremity, advanced lower-extremity, and upper-extremity subscales, respectively. Estimates for "substantial change" based on the global rating of change and minimal detectable change with 90% confidence were 5, 6, 9, and 10 points for the overall function scale and basic lower-extremity, advanced lower-extremity, and upper-extremity subscales, respectively.
CONCLUSION: This study provides the first MCID estimates for the LLFDI-FC, a widely used patient-reported measure of function. These values can be used to interpret the outcomes of longitudinal investigations of functional status in similar populations of community-dwelling older adults.