Factor structure and specific variance of the WPPSI subtests at six age levels

The Wechsler Preschool and Primary Scale of Intelligence (WPPSI) was factor analyzed at each of six age levels between 4 and 6½ years through the method of principal factors. A two-factor solution, corresponding essentially to Wechsler's a priori grouping of the subtests into a Verbal and nonverbal or Performance scale, best described the 11 WPPSI subtests at each age level. Examination of the common, specific, and error variance components of the subtests across age levels indicated adequate test specificity to allow for individual interpretation of all subtests except Information and Comprehension when the null hypothesis model of ipsative interpretation of individual tests is employed.