Two item response theory models for analysing normative forced-choice personality items.

This paper proposes two unidimensional item response theory (IRT) models for analysing normative forced-choice personality items. Both models are derived from a common theoretical framework and arise as a result of different assumptions regarding the mechanism of choice. The simplest mechanism gives rise to the one-parameter normal-ogive model. The second mechanism gives rise to a new IRT model, which is closely related to the Coombs-Zinnes probabilistic unfolding model. The second model is compared theoretically to the normal-ogive model in terms of item characteristic curves and amount of item information. Next, procedures for estimating the respondent and the item parameters in the second model are described. Finally, both models are empirically compared by using two well-known personality measures.