Factorially defined verbal and performance IQs derived from the WISC-R: Patterns of cognitive ability in normal and learning disabled children

Abstract

The axes of the first two dimensions of a principal components analysis of the normative data of the WISC-R were rotated through 45°. This resulted in two orthogonal continua which were interpreted as describing verbal and nonverbal intelligence respectively. Factor score coefficients were used to calculate Verbal Factorial IQs (VFIQs) and Performance Factorial IQs (PFIQs). In normal children, girls ( N=1100) prove to be reliably superior to boys ( N=1099) in VFIQ, whereas the reverse is the case for PFIQ. In a large group ( N=1050) of learning disabled (LD) children, VFIQ is reliably lower than in normal children, and there is also a reliable decline with age over the years 6–16. The LD boys ( N=744) are no different from the LD girls ( N=306) in VFIQ. In these LD groups the PFIQ is reliably lower than in the normal group at age 6, but rises to a normal level by age 8. The LD boys, overall, return higher PFIQ scores than the LD girls. These results can be used to evaluate the rival hypotheses of ‘deficit’ vs ‘developmental lag’ as a cause of learning disability.