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This study was based on the premise that much of the instability evident in research on infant emotionality/temperament is a function not so much of measurement error (as typically presumed) but lawful discontinuity. Infants who changed from high to low and from low to high levels of negative or positive emotionality between 3 and 9 months of age were compared with infants who remained stable during the period on distal measures of the family environment (prenatally and neonatally measured) and proximal measures of parent-infant interaction (3 months) thought to account for stability and change in infant emotionality and on 1-year infant-mother attachment security
Belsky et al. (Wed,) studied this question.