All counties with more than 100,000 residents were included in the analysis. The researchers concluded:
This relationship between voting Republican and having more babies is growing stronger over time. In 2012, a 10% increase in votes for Romney within a county saw an expected increase of 0.05 in the total fertility rate, compared to 0.09 in 2024. In the past 12 years, the geographic relationship between voting Republican and having more babies has grown by 85 percent...
We get a clear picture of the fertility gap when we divide counties into five groups with equal population along partisan lines. The 20% most Republican counties have an aggregate total fertility rate of 1.76. The 20% most Democratic counties have an aggregate total fertility rate of 1.37, less than the EU.
