The Reds and the Blues of having children

This is an interesting New York Times Op-Ed piece by David Brooks that was forwarded to me by my thesis adviser. It describes an interesting divide on the Red State/Blue State border: a difference in desired number of children. This relationship is most evident in this passage:

"You can see surprising political correlations. As Steve Sailer pointed out in The American Conservative, George Bush carried the 19 states with the highest white fertility rates, and 25 of the top 26. John Kerry won the 16 states with the lowest rates."

It's a pretty interesting article, although it seems to be written from the point of view of a natalist, as it does a lot to lavish goodwill. From the point of view of an economist, having experience studying the relationship between female income/rights and fertility, I find this passage to be the most important:

"Natalists resist the declining fertility trends not because of income, education or other socioeconomic characteristics. It's attitudes. People with larger families tend to attend religious services more often, and tend to have more traditional gender roles."

I would like to see research on this issue which takes into account the mother's income as opposed to a more tradition family income. What could be shrouded in this is a situation where we have well-educated mothers who assume "traditional roles" as housewives, and so have no obvious opportunity cost to having lots of children. The income effect is shrouded by a well-off husband. Of course, we'll be able to find examples to the contrary (many of my friends, for instance), as there are plenty of women who desire to have a high paying job AND lots of children (the feasibility of which may be questionable). However I bet the shrouded income effect dominates in the Red States.