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Abstract

in age (Reinert, 1970;Schaie et al., 1989;Werdelin and Stjernberg, 1995). The association between age and differentiation of abilities relates to the differentiation hypothesis (Garret, 1946) which suggests that abilities tend to cohere strongly in infancy and childhood, insofar as it is testable. When maturation proceeds, the factorial pattern of intelligence changes and intellectual abilities become more independent from each other.A useful approach to study the structure of intelligence is factor analysis. A factor model includes a set of common factors to explain the variance shared by various measurements and test-specific factors to explain any residual variance. In a second-order factor model the intercorrelation among the first-order common factors is explained by positing one or more second-order common factors. The intercorrelation among the variables is then decomposed into a part that is attributable to the first-order common factors and into a part that is attributable to the second-order common factors. The hierarchical factor model is a popular multivariate factor technique to examine the structure of INTRODUCTIONThe factor structure of genetic and environmental influences on specific cognitive abilities measured at one point of time in childhood is investigated in the present study. Six subtests of a Dutch intelligence test were administered to 5-year-old twins. The examination of cognitive abilities is particularly interesting during childhood when rapid accumulation of learning and experience takes place. In school, children are exposed to many novel environmental effects which act specifically on the development of their intellectual abilities. The accumulating effects of these environmental influences may result in a different pattern of cognitive abilities in groups of individuals varying Received 13 Jan. 1999-Final 3 Sept. 1999 The genetic and environmental factor structures of intellectual abilities in 5-year-old Dutch twins were examined. Six subtests of the RAKIT, a Dutch intelligence test, were administered to 209 twin pairs. The subtests were categorized as either verbal or nonverbal. The genetic covariance structure displayed a two-common factor structure including specific factors to account for subtest residual variance. The correlation between the genetic Verbal and genetic Nonverbal factors did not differ significantly from zero. The shared environmental influence displayed a single-common factor structure. Unique environmental influences did not contribute to the covariance between subtests and were specific in origin. Estimates of heritability of the subtests ranged from 15% to 56%. Shared environmental influences were significantly present, but were modest in magnitude. The phenotypic data was best described by an oblique two-factor model. This model was not mirrored in the factor structures found for either the genetic or environmental covariances.

Abstract

“…These results validate the use of parental report questionnaire data to assign zygosity even in infancy, and concur with other studies showing that the determination of zygosity in twins based on questionnaires can be done with a high degree of accuracy (for a review, see Rietveld, van Baal, Dolan, & Boomsma, 2000). For the sample used in this monograph, we used zygosity information assessed from DNA when it was available (34% of the total sample).…”

“It takes a village” to support the vocabulary development of children with multiple risk factors.

“…The association of maternal verbal ability with a child’s vocabulary may be partially genetically mediated (Rietveld, van Baal, Dolan, & Boomsma, 2000) and partially mediated by the language that the child is exposed to (Bornstein, Haynes, & Painter, 1998; Oxford & Spieker, 2006; Storch & Whitehurst, 2001). An early longitudinal study (Huttenlocher, Haight, Bryk, Seltzer, & Lyons, 1991), as well as subsequent studies of English-speaking and Spanish-speaking families (Hoff, 2006; Hurtado, Marchman, & Fernald, 2008; Song, Tamis-LeMonda, Yoshikawa, Kahana-Kalman, & Wu, 2012), provided strong evidence of the latter mediation.…”