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...

We investigate women's fertility, labor, and marriage market responses to large declines in child mortality in the U.S. Fertility declined on the intensive margin as expected. However, despite the increasing value of having at least one child, a larger share of women remained childless. We...