Genetic and environmental covariance structures among WISC-R subtests: A twin study

Genetic and environmental correlations among 11 Wechsler Intelligence Scale for Children-Revised (WISC-R) subtests were estimated from a sample of 143 twin pairs using the methodology of multivariate behavioral genetics. The genetic correlations among subtests varied in magnitude and exhibited a pattern similar to corresponding phenotypic correlations. Correlations due to within-pair environmental influences were generally small, whereas those due to shared environmental influences tended to be intermediate. Several hypotheses regarding the structures of the additive-genetic, common environmental, and within-pair environmental covariance matrices were tested and evidence for differential factor structures was obtained. A model hypothesizing a three-factor structure for the genetic covariance matrix, a single factor for the common environmental matrix, and a single factor plus specifics for the within-pair environmental matrix fit the data well. Thus, the three-factor phenotypic structure typically observed in Wechsler Intelligence Scale for Children (WISC) data may be due largely to genetic influences.