Validation of the Late-Life Function and Disability Instrument

Objectives: To assess the concurrent and predictive validity of the Late-Life Function and Disability Instrument (LLFDI). Design: Cross-sectional. Setting: University-based human physiology laboratory. Participants: One hundred one men and women aged 80.8+/-0.4. Measurements: A short physical performance battery (SPPB) and a self-paced 400-m walk (400-m W) were used as performance tests of lower extremity function. The LLFDI was used to assess self-reported function and physical disability. Partial correlations adjusted for age and body mass index were used to determine the concurrent and predictive validity of the LLFDI. Statistical significance was accepted at P<.004 using a testwise correction. Results: LLFDI Overall Function scores were moderately associated with the SPPB (r=0.65, P<.001), 400-m W gait speed (r=0.69, P<.001), and measures of lower extremity function. Correlations of the two lower extremity subscores of the LLFDI (correlation coefficient (r)=0.63-0.73, P<.001) were greater than for the LLFDI upper extremity subscores (r=0.19-0.26, P>.004). Performance measures of function predicted disability limitations in the range of r=0.37-0.44 (P<.001) and disability frequency in the range of r=0.16-0.20 (P>.004). Conclusion: These findings support the concurrent and predictive validity of the LLFDI. Results support the use of the LLFDI scales as a substitute for physical performance tests when self-report is a preferred data-collection format.