The third and fourth factors of the WISC-III: What they don't measure

Factor analysis of the Wechsler Intelligence Scale for Children-Third Edition (WISC-III) continues to demonstrate support for the Verbal, Performance, and Full Scale IQs, as well as for the Verbal Comprehension (VC) and Perceptual Organization (PO) factors. With the addition of the Symbol Search subtest, however, the factor analysis reported in the examiner's manual yielded two additional factors rather than just one. There is, however, no early evidence that the third and fourth factors are clinically interpretable. This study examined the relationship between the WISC-III third and four factors and other neuropsychological and behavioral measures. Results indicated that although Freedom From Distractibility (FFD) and Processing Speed (PS) correlated significantly with VC and PO factors, the FFD and PS factors did not correlate significantly with any of the other measures of attention. The most robust correlations were between measures of immediate/working memory and FFD and PS. When comparing clinical groups (LD/no ADHD, ADHD Predominantly Inattentive, and ADHD Combined Type), no differences emerged on the FFD or PS factors. The clinical validity of these factors remains questionable. The significant relationship between WISC-III factors and measures of immediate/working memory is promising, but in need of additional research.