Multivariate genetic analysis of Wechsler Intelligence Scale for Children--Revised (WISC-R) factors.

Wechsler Intelligence Scale for Children--Revised (WISC-R) factor scores (Verbal Comprehension, Perceptual Organization, and Freedom from Distractibility) were obtained from 574 twin pairs in the Colorado Reading Project and subjected to multivariate genetic analysis. Variances were partitioned into components common to the three WISC-R factors and to those specific to each factor. Substantial commonality, both genetic and environmental, was found among the three factors. The full model fit the data well, and estimates of heritability and environmentality indicated that about half of the phenotypic variance for each factor is due to additive genetic effects. These results were compared to those obtained in a previous twin study of the three Wechsler Adult Intelligence Scale (WAIS) factors by Tambs et al. (1986).