Effects of Proration on the Wisc Iqs of Mentally Retarded Children
Of the 12 subtests in the Wechsler Intelligence Scale for Children (WISC), only 10 were used to establish the IQ tables presented in the test manual (Wechsler, 1749). In the interest of shortening examination time, Digit Span was omitted from the Verbal Scale and Mazes from the Performance Scale, although E may substicute Mazes for Coding. Wechsler strongly advises that all 12 subcests be included in clinical situations, a procedure thac requires proracing before the IQs are computed. While Anderson (1753) has argued cogently against "including inferior material and prorating to find an IQ" (p. 478), no previous empirical study of the effects of proration has been found. All 12 subtests of the WISC were administered to 40 hospitalized retardates, 28 boys and 12 girls. Their mean age was 12.9 yr. (SD = 2.29), and their mean length of hospitalization, 2.4 yr. (SD = 1.76). For 28 of the children, there was no clinical or historical indication of organic disease or pathology. The mean Full Scale IQ of the sample was 50.4 (SD = 9.04). Verbal IQs were computed on the basis of the five subrests used by Wechsler in constructing the WISC norms, and also by prorating the Verbal Scaled Score on all six subtests, including Digir Span. Performance IQs were computed in an analogous fashion. The t rest for correlated measures was used to evaluate the significance of the differences berween five-subtest and six-subtest (prorated) 1Qs. '[iMs and SDs of subtest scores were: Info., 2.6 2 1.43; Comp., 2.8 2 1.94; Arith.,