Older and Wiser? Birth Order and IQ of Young Men

While recent research finds strong evidence that birth order affects children’s outcomes such as education and earnings, the evidence on the effects of birth order on IQ is decidedly mixed. This paper uses a large dataset on the population of Norway and focuses on the effect of birth order and family size on IQ, an outcome not previously available in datasets of this magnitude. Importantly, we find a strong and significant effect of birth order on IQ, and our results suggest that earlier born children have higher IQs.