The Quantity-Quality Trade-Off and the Formation of Cognitive and Non-Cognitive Skills

We estimate the impact of increases in family size on childhood and adult outcomes using matched mother-child data from the National Longitudinal Survey of Youth 1979. Using twins as an instrumental variable and panel data to control for omitted factors we find that families face a substantial quantity-quality trade-off: increases in family size decrease parental investment, decrease childhood cognitive abilities, and increase behavioral problems. The negative effects on cognitive abilities are much larger for girls while the detrimental effects on behavior are larger for boys. We also find evidence of heterogeneous effects by mother's AFQT score, with the negative effects on cognitive scores being much larger for children of mothers with low AFQT scores