18. Plomin, R., Campos, J., Corley, R., Emde, R. N., Fulker, D. W., Kagan, J., Reznick J. S., Robinson, J., Zahn-Waxler, C., & DeFries, J.C. (1990). Individual differences during the second year of life: The MacArthur Longitudinal Twin Study. In J. Colombo & J. Fagan (Eds.), Individual differences in infancy: Reliability, stability, prediction (pp 431-455). Hillsdale, NJ: Lawrence Erlbaum Associates.

This chapter describes the MacArthur Longitudinal Twin Study, a multivariate, longitudinal twin study that focuses on individual differences during the transition from infancy to early childhood. We report on preliminary findings in three areas: temperament, emotion, & cognition. Our assignment of measures to temperament, emotion, and cognition domains is not meant to imply that the variables are pure measures of a single domain or that these variables exhaust the multivariate diversity within each of the domains. Within the temperament domain, the emerging finding was that shyness and sociability are relatively independent. The multivariate nature of temperament no doubt extends far beyond these two dimensions and activity levels. Within the domain of emotion, the most interesting finding was that positive and negative tone are relatively independent dimensions of emotion as are reactivity to distress and empathy. In contrast, the domain of cognition indicated moderate overlap between mental development as assessed by the Bayley Mental Scales and language development as measured by the receptive and productive scales of the Sequenced Inventory of Communication Development. Across domains, measures of temperament showed no significant associations with measures of emotion or cognition at 14 months.