Birth weight effects on cognitive and non-cognitive development in early childhood: evidence from twins data

Empirical evidence has shown positive associations between birth weight and various outcomes, including health, educational attainment, earnings and cognitive development. However, most studies focus on later-life outcomes and rely on cross-sectional or sibling study designs, which have limited ability to control for unobserved variables that influence both birth weight and the outcomes of interest. This research aims to provide new empirical evidence on the effects of birth weight on cognitive and non-cognitive development, using data from singleton and twin births of children aged six months to seven years, based on a survey conducted in Chile. Results from Ordinary Least Squares models across families indicate positive associations between birth weight and developmental outcomes. However, first-difference models within twin pairs - which account for unobserved genetic and environmental factors - suggest that birth weight affects only language skills among the four developmental domains studied, and motor skills when focusing on the youngest children in the sample. The study also finds some evidence that birth weight may influence developmental outcomes indirectly through later measures of physical development. These findings should be interpreted as lower-bound estimates, as recent evidence suggests that twin studies tend to underestimate the true effects of birth weight.