Twin births are an important instrumental variable for the endogenous fertility decision. However, in many economic settings, twins are not exogenous as dizygotic twinning is known to be correlated with maternal characteristics and fertility treatments. Following the medical literature, we...

English Abstract: We document increased old-age mortality rates among Swedish twin mothers compared to non-twin mothers. Results are based on administrative data on mortality for the years 1990 to 2010. We argue that twins are an unplanned shock to fertility in the cohorts of older women...

In the presence of heteroskedasticity, conventional standard errors (which assume homoskedasticity) can be biased up or down. The most common form of heteroskedasticity leads to conventional standard errors that are too small. When Wald tests based on these standard errors are insignificant,...

This paper demonstrates that popular linear fixed-effects panel-data estimators are biased andinconsistent when applied in a discrete-time hazard setting - that is, one in which the outcomevariable is a binary dummy indicating an absorbing state, even if the data-generating process isfully...

English Abstract: Assumptions that are sufficient to identify local average treatment effects (LATEs) generate necessary conditions that allow instrument validity to be refuted. The degree to which instrument validity is violated, however, probably varies across subpopulations. In this paper, we...