Economists and demographers have long argued that fertility differs by income (differential fertility), and that social … security creates incentives for people to rear fewer children. Does the effect of social security on fertility differ by income …? How does social security change the cross-sectional relationship between fertility and income? Does social security …

The causal effects of fertility are a central focus in the social sciences, but the analysis is challenged by the … endogeneity of fertility choices. Earlier work has proposed several "natural experiments" from twin births or gender composition … rare (twins) and weak (gender composition) instrumental variables for fertility. This paper proposes a new "natural …