While recent research finds strong evidence that birth order affects children's outcomes such as education and earnings … earlier born children have higher IQs. Our preferred estimates suggest differences between first-borns and second-borns of … birth order effects occur because later-born children are more affected by family breakdown. …

How do families influence the ability of children? Cognitive skills have been shown to be a strong predictor of … to a better understanding of children's long run outcomes. This paper uses a large dataset on the male population of … resulting from twin births have negative effects on the IQ of existing children. …