Improved interpretation of stroke trial results using empirical Barthel item weights.

BACKGROUND AND PURPOSE Attempts have been made to provide guidelines for interpreting Barthel scores. We used a Rasch analysis to improve the measurement properties and clinical interpretability of the Barthel index score. METHODS A specific extension of Rasch model was used to identify items that preclude the summation of items and to improve the item rating scale by examining the scores on the Barthel of 559 stroke patients scored 3 weeks (n=89) and 6 months (n=470) after stroke. The clinical interpretation of the revised Rasch modeled Barthel was illustrated by re-examining the results of a previously published trial on the effectiveness of leg and arm training after stroke. RESULTS Most rating scales could be improved by collapsing nondiscriminating rating categories. Two items showed misfit: Bladder and Bowel. The remaining Barthel showed an excellent fit to the extended Rasch model (R1c Goodness-of-Fit P=0.35). Both items and patients could be placed on a common logit unit scale, allowing a clearer interpretation of the trial effect. Using the modeled activities of daily living difficulty/ability scale, we could express the differences between treatment arms in modeled probabilities of a positive score to each Barthel item for the treatment arms not conveyed by the original ordinal Barthel sum scores. CONCLUSIONS We improved the psychometric properties and clinical interpretation of the Barthel index.