Twin Temperament during the Transition from Infancy to Early Childhood

A multiple regression model for the analysis of twin data in which one twin's score is predicted from that of its co-twin, the coefficient of relationship, and the interaction term provides direct estimates of heritability (h 2) and the proportion of variance due to shared environmental influences (c 2). Several multiple-regression models were fitted to parental ratings of infant and toddler temperament for 306 pairs of twins. High estimates of h 2 were found for eight of the nine temperament scales, and three scales showed significant effects of c 2. No differential heritability was found between males and females across the infant and toddler years.