Temperament in full-term and preterm infants: stability over ages 6 to 24 months.

Temperament stability over successive ages in the first 2 years of life was evaluated for 109 full-term and 81 preterm infants who were assessed at 6, 9, 12, 18, and 24 months. At each age, the infant was engaged in a series of age-appropriate vignettes in the laboratory, using a structured sequence of activities. Ratings were made of emotional tone, attentiveness, activity, and orientation to staff. Correlations indicated that, for full-term infants, there was significant stability across ages (6 to 9 months, 9 to 12 months, 12 to 18 months, and 18 to 24 months) for all variables. For preterm infants, stability across ages generally was not observed until later infancy, or was sporadic. The findings indicated that, for full-term infants, stable aspects of temperament were apparent during the first year of life. In contrast, individual differences were not as clearly defined for preterm infants until later ages.