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 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 more than 18 million births (more than 500,000...

This paper suggests differential parental investment as a theoretical link between geographical conditions and comparative economic development, possibly accounting for the reversal of fortune in the process of development with respect to land productivity. The paper develops an evolutionary...

The lottery of birth draws some children into deprived environments and others into environments where they thrive. In a field experiment in rural India with 10-20 months old children we test two scalable interventions to reduce early disadvantages in health and mental development. We distribute...

The lottery of birth draws some children into deprived environments and others into environments where they thrive. In a field experiment in rural India with 10-20 months old children we test two scalable interventions to reduce early disadvantages in health and mental development. We distribute...

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...

Objective Better measurement of the health and cognitive benefits of breastfeeding by using sibling comparisons to reduce sample selection bias. Data We use data on the breastfeeding history, physical and emotional health, academic performance, cognitive ability, and demographic characteristics...