Two investigations of the validity of the WISC-III

Two studies were conducted in which the validity of the WISC-III was investigated. In Study 1, WISC-R and WISC-III IQs were correlated for a sample of 53 students, who, although originally meeting criteria for a disability category through use of the WISC-R, did not meet eligibility criteria upon reevaluation with the WISC-III. Corrected correlations between IQs were high, ranging from .80 to .87, and were comparable to figures reported in the WISC-III manual. Consistent with the WISC-III manual, WISC-III IQs were 8, 5, and 7 points lower than the WISC-R Full Scale, Verbal, and Performance IQs, respectively. In Study 2, the criterion validity of the WISC-III with the WRAT-R Reading, Spelling, and Arithmetic subscales and with the PPVT-R was investigated for a sample of 32 students with mental retardation. The WISC-III IQs and PPVT-R scores were highly correlated, sharing between 64 to 76% of variance. Correlations between WISC-III IQs and scores on the WRAT-R Reading and Arithmetic subscales were moderate. Surprisingly, the WISC-III IQs were not related to the WRAT-R Spelling scores. Implications of both studies for assessment specialists are discussed.