Item Response Models for Forced-Choice Questionnaires: A Common Framework

In forced-choice questionnaires, respondents have to make choices between two or more items presented at the same time. Several IRT models have been developed to link respondent choices to underlying psychological attributes, including the recent MUPP (Stark, Chernyshenko & Drasgow, 2005) and Thurstonian IRT (Brown & Maydeu-Olivares, 2011) models. In the present article, a common framework is proposed that describes forced-choice models along three axes: 1) the forced-choice format used; 2) the measurement model for the relationships between items and psychological attributes they measure; and 3) the decision model for choice behavior. Using the framework, fundamental properties of forced-choice measurement of individual differences are considered. It is shown that the scale origin for the attributes is generally identified in questionnaires using either unidimensional or multidimensional comparisons. Both dominance and ideal point models can be used to provide accurate forced-choice measurement; and the rules governing accurate person score estimation with these models are remarkably similar.