Fertility and the personal exemption

"One of the most commonly cited studies on the effect of child subsidies on fertility, Whittington, Alm, and Peters (1990), claimed a large positive effect of child tax benefits on fertility using time series methods. We revisit this question in light of recent increases in child tax benefits by replicating this earlier study and extending the analysis. We discuss two strong assumptions that were implicitly made in the original analysis and show that the earlier results vanish if either assumption fails to hold. Even if these assumptions hold, we show that the Whittington et al. results are not robust to more general measures of child tax benefits. While we do not find evidence that child tax benefits affect the level of fertility, we find some evidence that they affect fertility timing"--National Bureau of Economic Research web site.