The Causal Effect of Education on Age at First Birth - the Use of Danish Twin Data

Mette Gerster, University of Southern Denmark
Mette Ejrnæs, University of Copenhagen

Numerous studies have documented a strong correlation between women's educational attainment and fertility. Such a correlation might reflect a causal effect, but it might also simply be due to selection arising because of unobserved confounding. We use the Danish Danish Twin Registry to estimate the causal effect of educational attainment on age at first birth by means of a fixed effects duration analysis. This approach exploits the fact that monozygotic twins share all of their genes along with their early childhood environment and therefore, intra-pair comparisons of the effect of education on AFB will control for such unobserved endowments possibly influencing both education and fertility. A comparison with a standard model will provide evidence as to whether selection mechanisms are in play. Furthermore, carrying out the same comparison for dizygotic twins will point to whether unobserved heterogeneity arises due to genetic or environmental factors, e.g. childhood conditions.