A probabilistic IRT model for unfolding preference data

Abstract

A probabilistic model is developed for the pair-comparison design in which the unfolding principle that governs the choice process uses a discriminal process analogous to Thurstone’s Law of Comparative Judgment. However, this process is governed by the square of the distance between the location of the person and the stimulus, rather than controlled by the location of the stimulus as in Thurstone’s formulation. A simulation study demonstrates the feasibility of estimation, and two examples use real data to show the implications of the unfolding models for psychological research. Index terms: choice data, item response theory, pair comparisons, preference data, unfolding.