A measure of association for assessing prediction accuracy that is a generalization of non-parametric ROC area

There is a need for a measure of prediction accuracy that generalizes non-parametric receiver operating characteristic (ROC) area to polytomous ordinal patient state. We describe such a measure, prediction probability PK derived from Kim's measure of association. We show that the value of PK equals the value of non-parametric ROC area for dichotomous patient state and is a meaningful generalization of non-parametric ROC area for polytomous state.