Ratings of temperament in families of young twins

Abstract

We studied a sample of 576 pairs of twins in three age groups (0–2, 2–5, 5+ years), and obtained for each family a set of temperament ratings which provided isomorphic dimensions for parents and children (EASI Temperament Survey). Both parents were asked to rate independently themselves, their spouse and each of the twin children. The results confirm the findings of Lyon & Plomin (1981) that parental projection does not take place in the rating of each other. Only the mothers' rating of Emotionality shows any indications of projection in the rating of children, and parental agreement on children's temperament shows modest levels of reliability (r = 0·53). There is no evidence of assortative mating for temperament characteristics. The intra‐class correlations for monozygotic and dizygotic twins are consistent with Emotionality and Sociability being under some genetic control only in girls, Activity shows increasing genetic influences with age in both boys and girls, and Impulsivity indicates a lower level of genetically determined variance at all ages in both sexes. We concluded that, in common with recent studies on environment associations with temperament, the origin of individual differences needs to be studied separately in boys and girls. A more general case is made for the utility of twin studies that include data on other family members.