Rasch analysis of combining two indices to assess comprehensive ADL function in stroke patients

Background and Purpose-To justify the summation of scores representing comprehensive activities of daily living (ADL) function, a Rasch analysis was performed to examine whether items of the Barthel Index (BI), assessing ADL, and items of the Frenchay Activities Index (FAI), assessing instrumental ADL, contribute jointly to a single, unidimensional construct in stroke patients living in the community. The number of scoring points of both indices was examined for their usefulness in discerning the various ability levels of ADL in these patients. Methods-A total of 245 patients at 1 year after stroke participated in this study. The BI and FAI were administered to the patient and/or the patient's main caregiver by interview. Results-The initial Rasch analysis indicated that the middle scoring points for many items of the BI and FAI could be collapsed to allow only dichotomous response categories. All but 2 items of the FAI, social occasions and walking outside, fitted the model's expectations rather well. These 2 items were excluded from further analysis. A factor analysis performed on the residuals of the Rasch-transformed scores recovered no dominant component. These results indicate that the combined 23 dichotomous items of the BI and FAI assess a single unidimensional ADL function. Conclusions-A clinically useful assessment of the comprehensive ADL function of patients at or later than 1 year after stroke can be obtained by combining the items of the BI and FAI (excluding 2 FAI items) and simplifying the responses into dichotomous categories. It is also demonstrated that the items of the new scale measure comprehensive ADL function as a single unidimensional construct when assessed at 1 year after stroke.