We compared the extent to which the long-term influence of family socioeconomic status (SES) on children's school performance from age 7 through 16 years was mediated by their preschool verbal and nonverbal ability. In 661 British children, who completed 17 researcher-administered ability tests at age 4.5 years, SES correlated more strongly with…

A 2003 paper in this journal reported results from a large sample of twins assessed at 2, 3 and 4 years of age on parent-administered tests and reports of their verbal and nonverbal ability. We found clear evidence for phenotypic general cognitive ability (g) that accounted for about 50% of the variance, for modest genetic influence on g (about…

Sex differences and their relationship to individual differences were examined for Maccoby and Jacklin's sex differences summaries, for a diverse set of measures of specific cognitive abilities (including verbal ability), and for objective personality assessments of 216 school-age children. Average differences between groups appeared to be trivial…

A telephone test battery to assess verbal, spatial, and memory ability and perceptual speed in adolescents was developed. Test materials were mailed to 212 adolescents (members of 54 adoptive and 52 nonadoptive sibling pairs). Results show that telephone testing can be satisfactorily used to assess specific cognitive abilities with less anxiety…

The study of genotype-environment interaction (G x E) has been dominated by two competing hypotheses, one that heritability is greater in high-risk environments (diathesis-stress) and the other that heritability is greater in permissive environments. The current study examined relationships between verbal and nonverbal abilities and 10 measured…

Examined infant verbal and nonverbal cognitive development for 1,937 pairs of same-sex 2-year-old twins. Found that verbal and nonverbal development correlated .42. Genetic factors were responsible for less than half of this phenotypic correlation. The genetic correlation between verbal and nonverbal abilities was only .30, suggesting that genetic…

We report the first major genetic study of mild mental impairment. From a representative sample of 3,886 twins (1,314 monozygotic, 1,296 dizygotic same-sex, and 1,276 dizygotic opposite-sex), the lowest 5% were selected on a composite measure of verbal and nonverbal abilities assessed by parents when the twins were 2, 3, and 4 years of age. Twin…

Language development was studied in 310 pairs of 4-year-old twins. Rotated factor analyses indicated presence of a general language factor (L) and a general nonverbal factor (NV). Moderate genetic influence was found for L and NV abilities. Bivariate genetic analysis estimated a genetic correlation of .63 between L and NV abilities. Results…

Collected data on twins' performance on 13 cognitive variables measured three times at three-year intervals. Twins were monozygotic or dizygotic pairs reared together or apart and were in six cohorts ranging in age from 41 through 84 years. Found stable mean cognitive performance across time on eight measures for the younger cohorts, and…

Background: Five DNA markers (single-nucleotide polymorphisms, SNPs) have recently been found to be associated with general cognitive ability "g") in a sample of 7414 7-year-old twins. These children have also been studied at 2, 3, 4, and 7 years of age on measures of cognitive and language development and behaviour problems; family environment…