A twin and family study of personality in young children.

Emotionality, activity, sociability and impulsivity (EASI) and components of each trait were studied in a sample of 137 pairs of young twins (two to six years of age) and their parents (548 individuals). Parents rated themselves and their spouses on an adult version of the EASI Temperament Survey and rated both of their twins on a child version of the EASI. Patterns of both identical and fraternal twin correlations (twin study) and parent-child correlations (family study) were consistent with the hypothesis that the EASI traits are influenced by genetic factors, but the two studies disagreed in the magnitude of that influence.