Key points are not available for this paper at this time.
Robert N. Emde, Robert Plomin, JoAnn Robinson, Robin Corley, John DeFries, David W. Fulker, J. Steven Reznick, Joseph Campos, Jerome Kagan, Carolyn Zahn-Waxler, Temperament, Emotion, and Cognition at Fourteen Months: The MacArthur Longitudinal Twin Study, Child Development, Vol. 63, No. 6 (Dec., 1992), pp. 1437-1455
Emde et al. (Tue,) studied this question.