Measuring disability and function in individuals with multiple sclerosis: Psychometric properties of the abbreviated late-life function and disability instrument

The measurement of functional limitations and disability in individuals with multiplesclerosis (MS) has been plagued by definitional ambiguity and measurement limitations.The abbreviated Late Life-Function and Disability Inventory (LL-FDI) was recentlydeveloped based on accepted definitions of functional limitations and disability, and hasbeen supported as having strong measurement properties in samples of older adults. Thisstudy examined the structural and external aspects of score validity for the LL-FDI inindividuals with MS. Individuals with MS completed the LL-FDI and three measures ofphysical activity. Structural aspects of score validity for the LL-FDI were establishedusing confirmatory factor analysis (CFA). The CFA supported the existence of twofactors of personal and social aspects of disability for the disability frequency andlimitations subscales of the LL-FDI, and three factors of upper extremity function, basiclower extremity function, and advanced lower extremity function for the functionallimitations subscale of the LL-FDI. External aspects of score validity for the LL-FDIwere established based on expected differences in mean scores between individuals withrelapsing-remitting MS and primary and secondary progressive MS and examination ofthe pattern of correlations between mean scores with the measures of physical activity.Our results support the structural and external aspects of score validity for the LL-FDI inindividuals with MS, and we recommend that future researchers use this scale whenmeasuring functional limitations and disability in this population.