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Do changes in tax policy lead to more births?

In a recent op-ed for the Wall Street Journal, Rick Santorum proposed his "pro-growth and pro-family Economic Freedom Agenda."

"To help families, I'll triple the personal deduction for children and eliminate the marriage tax penalty," wrote Santorum.

But do changes in tax policy really lead to more births?

Kevin Drum, a politics blogger at Mother Jones, doesn't think so.

"If you want to reward people for having children just because you think it's the right thing to do, that's fine. But if you're actually trying to affect the number of kids we have, the evidence suggests it simply doesn't make any difference," said Drum.

Drum cited a 2010 National Bureau of Economic Research paper, in which the authors said they did not find evidence that child tax benefits affect the level of fertility.

The report noted the average value of child tax subsidies have skyrocketed, from under $850 in 1980 to more than $2,000 in 2005. Yet the general fertility rate is the same as it was in 1980. The stastics were made clear in a graph.

"This is just a chart showing that we've had sweeping waves of social and economic trends over the decades that totally swamp tweaks in the tax code," said Matthew Yglesias, a writer for Slate.

Because children are financially costly, of course a subsidy will make a difference to parents on the margin, Yglesias argued.

"But sometimes common sense is wrong, and sometime incentive effects, no matter how theoretically compelling, are small enough that they don't really matter in the real world," Drum countered.