Ten days after our baby entered the world, the latest copy of the Quarterly Journal of Economics landed in my inbox. It includes a paper I hadn’t seen before – “From the Cradle to the Labor Market? The Effect of Birth Weight on Adult Outcomes”. Here’s the abstract, from a previous working paper version:
Lower birth weight babies have worse outcomes, both short-run in terms of one-year mortality rates and longer run in terms of educational attainment and earnings. However, recent research has called into question whether birth weight itself is important or whether it simply reflects other hard-to-measure characteristics. By applying within twin techniques using a unique dataset from Norway, we examine both short-run and long-run outcomes for the same cohorts. We find that birth weight does matter; very small short-run fixed effect estimates can be misleading because longer-run effects on outcomes such as height, IQ, earnings, and education are significant and similar in magnitude to OLS estimates. Our estimates suggest that eliminating birth weight differences between socio-economic groups would have sizeable effects on the later outcomes of children from poorer families.
Our lad was about 20% above the average birthweight.Â The Black, Devereux and Salvanes results suggest that he will therefore earn 2% more than an average birthweight baby.Â What they can’t work out is the causal channel. Does this happen because of some causal effect of health on wages, or because parents and schools invest more in bigger kids?