Quantitative lunch -- Sean Womack via Zoom.

Twins regularly score nearly a standard deviation below the population mean on standardized measures of cognitive development in infancy, but exhibit average abilities by early childhood. Building on early observations of increases in mean intelligence scores over time (Wilson, 1974), the present study applies contemporary nonlinear growth methods to quantify the rate and shape of recovery of cognitive abilities in a large prospective sample of twins from 3 months to 15 years. Polynomial, exponential, and sigmoid growth models were fit to the data. The s-shaped Gompertz model fit the data best, yielding information on the average lower asymptote, total growth, rate of approach to the asymptote, and age of steepest growth. Twins in the present sample exhibited initial cognitive abilities 0.89 standard deviations below the population mean, but scored at the population mean by age 6. Cognitive growth was most rapid at 3.27 years. Biometric analyses revealed that shared environmental factors accounted for the majority of the variance in initial cognitive abilities as well as growth in cognitive abilities. Twins born prematurely scored significantly lower than full-term twins on cognitive assessments in infancy, but caught up by three years. Family SES was positively related to total growth in cognitive abilities. Children in low-SES homes exhibited a two year delay in their most rapid growth relative to children in high-SES homes. This ultimately led to an 8-point difference (0.53 standard deviations) in cognitive abilities between children in high-SES and low-SES homes. Findings highlight the importance of prenatal factors and family economic resources in cognitive development.