Differences between WISC-III and WISC-R IQs: A Preliminary Investigation

Abstract

Differences between WISC-III and WISC-R IQs of 257 children (1 18 with Specific Learning Disability, 79 with Mental Retardation, and 60 who were not classified as disabled) were examined. As anticipated, the WISC-III and WISC-R IQs were highly correlated, ranging from .84 for the Full Scale IQs to .80 for the Performance IQs. The WISC-III Full Scale, Verbal, and Performance IQs were 7.2, 5.8, and 7.5 points lower than corresponding WISC-R values. The size of the difference between WISC-III and WISC-R IQs was correlated significantly with WISC-R (r = .34) and WISC-III (r = -.23) IQs. Differences in the size of the IQ drop were in part a function of disability group membership: Students with learning disabilities differed in the likelihood of increases and decreases in IQs in comparison to students with mental retardation. Sex was unrelated to the size of the IQ drop. Amount and direction of change were predicted by subtest scores. Importantly, high Object Assembly and Coding scores were primary factors in predicting increases in IQ, and higher Vocabulary scores predicted decreases in IQ.