Two- and three-factor solutions of the WAIS-III

The third edition of the Wechsler Adult Intelligence Scale manual reports four-factor solutions for the WAIS-III, and subsequent research has validated four-factor solutions for a variety of samples. These four factors consistently correspond to the four Factor Indexes that are yielded by the WAIS-III. However, the WAIS-III still provides Verbal and Performance IQs, in addition to the Indexes, making it desirable to examine two-factor solutions as well. In addition, because the Wechsler literature includes much interpretation of three-factor solutions, these solutions were likewise examined. Principal factor analysis followed by Varimax and Oblimin rotations of two and three factors were performed on data for the total WAIS-III sample ages 16 to 89 years (N=2,450). The two-factor solutions were viewed as a construct validation of Wechsler's two separate IQs, although the Working Memory subtests tended to load higher on the Performance scale than on their intended scale (Verbal); three-factor solutions were interpreted within the context of Horn's expanded fluid-crystallized theory and research on working memory. Both the two- and three-factor Varimax-rotated solutions were related to similar factor analyses conducted previously for the Wechsler Adult Intelligence Scale-Revised and the Wechsler Intelligence Scale for Children-III. Coefficients of congruence between like-named factors consistently exceeded .90, and usually .98, across different Wechsler batteries.