Rated personality and measured intelligence in young twin children

Phenotypic, genetic, and environmental correlations between measured intelligence and caregiver-provided ratings of personality were examined in a sample of 4- to 6-year-old twin children (N = 680 individuals). Personality ratings were factor analyzed. Five factors were extracted and labelled: agreeableness, extraversion, neuroticism, conscientiousness, and psychoticism. Univariate genetic analyses conducted on the same-sex pairs (101 MZ pairs and 132 same-sex DZ pairs) demonstrated that all of the personality factors had heritable components (range = 31–86%). Performance and full-scale intelligence were also found to have heritable components, but verbal intelligence was better explained by environmental factors. At the phenotypic level, agreeableness and conscientiousness correlated positively with intelligence and neuroticism and psychoticism correlated negatively with intelligence. Multivariate genetic analyses revealed that some of the observed phenotypic correlations could be explained by common genetic factors.