ABSTRACT
The notion of “unfolding models” for item responses dates back to at least the early attitude measurement work of Thurstone (Thurstone, 1928, 1931, 1932; Thurstone and Chave, 1929) where he assumed that a “relevant” attitude statement attracted endorsements from those individuals whose opinion was matched well by the statement content. Thurstone represented the locations of both persons and items on an underlying unidimensional attitude continuum in which a person was located on the basis of his or her attitude and an item was located according to its content. Thurstone's idea gave rise to single-peaked, empirical item response functions in which persons were more likely to endorse attitude statements to the extent that they were located at nearby positions on the underlying continuum. It was an implicit model for item responses that followed from a proximity-based response process (Roberts et al., 1999).
