Three papers--comments, a reply to comments, and a rejoinder--discussing a conclusion about the nature of general intelligence based on the size loadings of a psychomotor test of discrimination reaction time are presented. The use of Spearman's "g" is the center of the controversy. (TJH)

A probabilistic item response theory (IRT) model is developed for pair-comparison design in which the unfolding principle governing the choice process uses a discriminant process analogous to Thurstone's Law of Comparative Judgment. A simulation study demonstrates the feasibility of estimation, and two examples illustrate the implications for…