Evidence-based measurement: which disability scale for neurologic rehabilitation?

OBJECTIVE: To compare the 10-item Barthel Index (BI), 18-item Functional Independence Measure (FIM), and 30-item Functional Independence Measure + Functional Assessment Measure (FIM+FAM) as measures of disability outcomes for neurologic rehabilitation. METHODS: A total of 149 inpatients from two rehabilitation units in South England specializing in neurologic disorders were studied. Traditional psychometric methods were used to evaluate and compare acceptability (score distributions), reliability (internal consistency, intrarater reproducibility), validity (concurrent, convergent and discriminant construct), and responsiveness (standardized response mean). RESULTS: All three rating scales satisfied recommended criteria for reliable and valid measurement of disability, and are acceptable and responsive in this study sample. The FIM and FIM+FAM total scales are psychometrically similar measures of global disability. The BI, FIM, and FIM+FAM motor scales are psychometrically similar measures of physical disability. The FIM and FIM+FAM cognitive scales are psychometrically similar measures of physical disability. CONCLUSIONS: In the sample studied, the BI, FIM, FIM+FAM have similar measurement properties, when examined using traditional psychometric analyses. Although instruments with more items and item response categories generate more qualitative information about an outcome, they may not improve its measurement. Results highlight the importance of using recognized techniques of scale construction to develop health outcome measures.