On the comparison of group performance with categorical data

This paper provides a criterion to evaluate the overall performance of a given number of groups whose members can be of different types, out of the analysis of their relative frequencies. Assuming that types can be ordered from best to worse, the starting point is that of dominance relations in pair-wise comparisons. We say that group i dominates group j when the expected type of a member of i is higher than the expected type of a member of j. To extend this principle to multi-group comparisons we introduce the notion of relative advantage of a group and show that there is a unique evaluation function that ranks consistently all groups in terms of this criterion. This function associates, to each evaluation problem, the (unique) dominant eigenvector of a matrix whose entries describe the dominance relations between groups in pairwise comparisons. An application to education illustrates the working of this model.