A function used in models for ordinal variables. Let j denote a possible value of the ordinal variable, Y, and let E1 and E2 be two possible events. The ratio Rj, given byis called a cumulative odds ratio (see two-by-two table). If E1 and E2 represent different values for a vector of explanatory variables, the model Rj=R, where R is a constant, is a proportional-odds model.