Developmental research of twin's temperament.

In the Louisville Twin Study, pairs of 3- and 4-year-old twins were provided with standardized competitive or cooperative tasks in a laboratory setting. Some tasks required a pair of twins to share toys; other fostered a more competitive engagement between the twins. Behavioral ratings identified temperament and social components at both ages, and between the two ages, there were transformations in the links between the components. Parental ratings of the twins' temperament at the same ages were moderately correlated with the laboratory observations, but the pattern of the relations changed from one age to the next. The combined sets of measures were subjected to twin analyses for 43 pairs of twins. The results are discussed in terms of the similarity of MZ and DZ pairs for the dimensions of temperament and the transformations of temperament.