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One study that illustrates how screwed up America's approach to family life is

Lady. Any more kids and you'll fall years behind at work.
Lady. Any more kids and you'll fall years behind at work.
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Women, you really can have both a family and a fulfilling career. You just have to do it just right. (Men, you get more freedom.) A new study from the Federal Reserve Bank of St. Louis looks into how having a family affects women and men. As it turns out, it's complicated.

The study (a hat-tip to Wonkblog's Ylan Q. Mui for highlighting it) focuses on academic economists and finds that moms are more productive than non-moms throughout their careers. But having a kid at the wrong time — or alone — or having too many kids — can make a mother far, far less productive.

What they studied

Researchers looked at the research output of economists, measuring the impacts of their publications by using RePEc, an online database of economics papers. They created indexes to measure the impact of those economists' research, then matched that data up with the more than 10,000 responses they received to surveys asking detailed questions about the economists' academic careers, as well as family lives — when children were born, how many there are, and how it affected their work lives.

What they found

First, the simplest finding: "We find in our entire sample of about 10,000 male and female economists that men's productivity is not associated with their family situation in an economically significant manner." In fact, they find a small uptick in productivity for untenured men who become fathers — an uptick that may be attributable to the "provider effect," says Krapf: these men may feel added pressure to produce once they have kids.

The situation is more complicated for women. First off, moms are more productive than non-moms throughout their careers. The below charts show childless, one-child, and multiple-child women's productivity as measured by a publication index the authors created for this report.

women productivity

(Source: Krapf et al.)

It's not all bad news: researchers found that a mom's first child is not significantly associated with a hit to the mother's productivity. But more kids change that outcome. The authors write that the results imply "a mother of three children has, on average, a research record reflecting a loss of four years of research output by the time all of her children have reached their teens." A mother of two, likewise, has a 2.5-year loss of output.

But even if a woman does only have one child, there are other factors that can drag on her productivity. Childrens' ages matter, too, for example. Moms of young children, for example, see their productivity drop off 15 to 17 percent, compared to childless women.

And family planning plays a huge role. Having a kid before age 30 is associated with a drag on productivity by 13 percent, and unintended pregnancy (which they define as pregnancies in unpartnered moms who were uninformed about their childcare options) pulls productivity down 13 to 17 percent. Meanwhile, there's no effect for women having kids in their early 30s, and only a small (but statistically insignificant) effect for women in their late 30s.

With all that taken into account, it appears there's a specific window in which to have the optimal family, so long as it's small: "Women who become mothers in the 30- to 34-year age bracket fare substantially better; having an only child at that time of their careers does not appear to be detrimental to their research productivity," the authors write.

So 29-to-33-year-old childless-and-married ladies should get cracking.

What it means

There are a few big questions this study raises: for example, despite the obvious productivity hits they suffer form having kids, moms seem to remain more productive throughout their academic careers. Why?

One reason for this, says one of the paper's authors, could be the types of women likely to have kids: "The most likely reason may be selection, i.e. women who are more productive in the first place may be more likely to become mothers," says Matthias Krapf, a professor at the University of Zurich.

But it also implies what many women already know: that they have to think really, really hard about how to manage their working lives once they have kids — more so than men do.

"All of these results suggest that a first child need not destroy any academic career plans. Female academics who carefully project ahead and responsibly orchestrate their private lives appear to be well able to cope with motherhood — at least when they have only one child," the authors write.

What it doesn't mean

First off, it would be hard to generalize this study to all working women in the US. This is a study of academics — people for whom it's likely easier to have kids than, say, for minimum wage workers, thanks to all sorts of factors like higher pay, job security, access to child care, and paid family leave.

Furthermore, it doesn't mean motherhood is exactly great for a woman's career. Several studies have found evidence of a motherhood penalty. In addition, despite the fact that it's illegal to discriminate against pregnant women, complaints about this type of discrimination are still commonplace, 36 years after it became illegal.

In addition, the authors point out that there could be something misleading in the data showing all those super-productive late-career moms.

"[O]ur results are sensitive to survivor bias, i.e., women who become most unproductive and quit the profession after becoming mothers are not included in our sample," writes Krapf. In other words, if kids really kill a woman's productivity, she might drop out, leaving only the most uber-productive moms at the office.