It is common to assess disability and handicap of stroke patients using standardized scales. Two such scales are the Rankin Stroke Outcome Scale (RS) and the Barthel ADL Index (BI). The Rankin Scale, which was designed for applications to stroke, is based on assessing directly the global conditions of a patient. The Barthel Index, which was designed for more general applications, is based on a series of questions about the patient's ability to carry out 10 basic activities of daily living. As both scales are commonly used, but few studies use both, translating between scales is important in gaining an overall understanding of the efficacy of alternative treatments, and in developing prognostic models that combine several data sets. The objective of our analysis is to provide a tool for translating between BI and RS. Specifically, we estimate the conditional probability distributions of each given the other. Subjects consisted of 459 individuals who sustained a stroke and who were recruited for the Kansas City Stroke Study from 1995 to 1998. Patients were assessed with BI and RS measures 0,1,3 and 6 months after stroke. In addition, we incorporated a published table cross-classifying patients by RS and coarsely aggregated BI. Our statistical estimation approach is motivated by several goals: (a) overcoming the difficulty presented by the fact that the two data sources report data at different resolutions; (b) smoothing the empirical counts to provide estimates of probabilities in regions of the table that are sparsely populated; (c) avoiding estimates that would conflict with medical knowledge about the relationship between the two tests and (d) estimate the relationship between RS and BI at three months after the stroke, while borrowing strength from measurements made at one and six months. Our results provide the basis for comparing and integrating the results of clinical trials using different disability measures, and for integrating clinical trials results into comprehensive decision model for the assessment of long term implications and cost-effectiveness of stroke prevention and acute treatment interventions. In addition, our results indicate that the degree of agreement between the two measures is less strong than commonly reported.

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