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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
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Emde et al. (1992) studied this question.
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