Twin births are often construed as a natural experiment in the social and natural sciences on the premise that their occurrence is quasi-random. We present new population-level evidence challenging this premise. Using data on about 18 million births in 72 countries, we find that maternal...

Twin births are often construed as a natural experiment in the social and natural sciences on the premise that the occurrence of twins is quasi-random. We present new population-level evidence that challenges this premise. Using individual data for 17 million births in 72 countries, we...

In vitro fertilization (IVF) has allowed women to delay birth and pursue a career, but it massively increasesthe risk of twin birth. We investigate the extent to which having twins hampers women's careers after birth. To do this, we leverage a single embryo transfer (SET) mandate for IVF...

We analyze long-term impacts of the 1967-1970 Nigerian Civil War, providing the first evidence of intergenerational impacts. Women exposed to the war in their growing years exhibit reduced adult stature, increased likelihood of being overweight, earlier age at first birth, and lower educational...

We investigate the importance of subjective expectations of returns to and effort costs of the two main investments that mothers make in newborns: breastfeeding and stimulation. We find heterogeneity across mothers in expected effort costs and expected returns for outcomes in the cognitive,...

Twin births are often construed as a natural experiment in the social and natural sciences on the premise that the occurrence of twins is quasi-random. We present new population-level evidence that challenges this premise. Using individual data for more than 18 million births (more than 500,000...

We investigate universalization of access to health in Brazil. We find large reductions in maternal, foetal, neonatal and post-neonatal mortality, a reduction in fertility and, possibly on account of selection, no change in the quality of births. Using rich administrative data, we investigate...

Twin births are often construed as a natural experiment in the social and natural sciences on the premise that the occurrence of twins is quasi-random. We present new population-level evidence that challenges this premise. Using individual data for 17 million births in 72 countries, we...

Twin births are often used to instrument fertility to address (negative) selection of women into fertility. However recent work shows positive selection of women into twin birth. Thus, while OLS estimates will tend to be downward biased, twin-IV estimates will tend to be upward biased. This is...

IVF allows women to delay birth and pursue careers, but IVF massively increases the risk of twin birth. There is limited evidence of how having twins influences women's post-birth careers. We investigate this, leveraging a single embryo transfer (SET) mandate implemented in Sweden in 2003,...