Special Unfolding Models

Abstract

In this chapter, some special unfolding models are discussed. First, we distinguish internal and external unfolding. In the latter, one first derives an MDS configuration of the choice objects from proximity data and afterwards inserts ideal points to represent preference data. Then, the vector model for unfolding is introduced as a special case of the ideal-point model. In the vector model, individuals are represented by vectors and choice objects as points such that the projections of the objects on an individual’s vector correspond to his or her preference scores. Then, in weighted unfolding, dimensional weights are chosen freely for each individual. A closer investigation reveals that these weights must be positive to yield a sensible model. A variant of metric unfolding is discussed that builds on the BTL choice theory.