A simple probabilistic model for unfolding data collected by a direct response design in which responses were scored dichotomously was applied to the measurement of attitudes toward capital punishment. Responses conformed to the unfolding mechanism. Scale values of the statements were statistically equivalent to those of Thurstone's methods. (SLD)

A probabilistic item response theory (IRT) model is developed for pair-comparison design in which the unfolding principle governing the choice process uses a discriminant process analogous to Thurstone's Law of Comparative Judgment. A simulation study demonstrates the feasibility of estimation, and two examples illustrate the implications for…