Predicting variation in the timing of language milestones in the second year: an events history approach.

In a longitudinal investigation of 40 child-mother dyads, we examined prediction from three indexes of children's own language: (1) vocal imitations, (2) first spontaneous words in production, and (3) receptive language starting at 0;9, and their mothers' verbal responsiveness at 0;9 and 1;1, to the developmental onset of three significant language milestones of the second year: (1) 50 words in productive language, (2) combinatorial speech, and (3) the use of language to express a memory. In these analyses, we utilized EVENTS HISTORY ANALYSIS, a statistical technique well suited to questions concerning when in development certain events begin and the extent to which predictors influence the timing of those events. The timing of children's first words in production, the timing of their achievement of 50 words in receptive language, and maternal responsiveness at 1;1 each contributed uniquely to variation in the timing of the three language milestones. When child and mother factors were considered together, the onset of the three language milestones differed by as much as 0;5 months for children in the lower and upper 10th percentiles of the predictor variables. The present findings contribute to generating and testing specific models about child and mother factors thought to explain variation in key aspects of children's second-year language development.

Twin temperament during the transition from infancy to early childhood.

A multiple-regression model for the analysis of twin data in which one twin's score is predicted from that of its co-twin, the coefficient of relationship, and the interaction term provides direct estimates of heritability (h2) and the proportion of variance due to shared environmental influences (c2). Several multiple-regression models were fitted to parental ratings of infant and toddler temperament for 306 pairs of twins. High estimates of h2 were found for eight of the nine temperament scales, and three scales showed significant effects of c2. No differential heritability was found between males and females across the infant and toddler years.