Differences between WISC-R and WISC-III performance scale among children with ADHD

Reviews involving the Wechsler Scales for children suggest that Full Scale IQ scores on the Wechsler Intelligence Scale for Children, Third Edition, average 5 to 6 points lower than scores on the second edition of the scale [WISC-R, Wechsler, D. (1974). Zimmerman & Woo-Sam, 1997], with the differences distributed disproportionately over subtests, i.e., with larger discrepancies found within the Performance Scale (Wechsler, 1991). Changes on the revised subtests of the WISC-III Performance Scale may place children with ADHD at a disadvantage compared to their performance on analogous WISC-R subtests. We examined IQ test performance in 122 unmedicated children with ADHD (61 given the WISC-R, 61 given the WISC-III), and 46 children from a healthy, comparison group (23 given the WISC-R, 23 given the WISC-III). The ADHD and comparison group samples were matched for sex and for Verbal IQ between WISC-R and WISC-III. Children with ADHD had significantly lower Performance IQ on WISC-III compared to the WISC-R, with the Picture Arrangement subtest showing the most significant difference. In contrast, there were no significant differences between the WISC-R and WISC-III cohorts on Performance IQ or any Performance subtests among the comparison group. These findings highlight the importance of examining the comparability of ability test revisions among clinical and non-clinical populations, and will be especially salient when the WISC-III is revised.