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May 07, 2015


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Anecdotal: I've heard a lot of people state they want more kids and I'm normally in the midst of geeks and techies. This is echoed by both men and women. The primary problem has been $.

(again anecdotal)

Perhaps its tied to the uptick in the economy?

The uptick theory, not so sure. Most American women are still having kids between 22 and 35, meaning this cohort's peak childbearing years were 1997 to 2010.


Doug M.

Maybe it's just that more women are getting postgraduate degrees, so that group is becoming more representative of all women.

Gareth: good hypothesis! I went to the census bureau and checked it. (See Table 1.)

Of women aged 40-44 in 2014, 13.8% had postgraduate degrees.

Of women aged 60-64 in 2014, 13.2% had postgraduate degrees. (These women were aged 40-44 in 1994.)

That's not a big enough change to affect the results.

Two possibilities come to the top of my head:

1) I suspect there is a change, that starts before this period, in people's perception (including women's own) about women being able to both be serous about a career and raise children. So women were more likely to select into one or the other (including after the fact, that is, once they had the degree, finding it hard to make time, or to date or etc.).

2) Fertility technology has improved. There was a group that wanted kids, but found that age related fertility decline made them unable, but the younger group was able to have children because of this technology.

Fair enough.

The 2008 recession lowered the returns to career, so many women in two-career families decided to take the "mommy track."

That seems improbable. This cohort of women was aged 34-38 in 2008; they would have had to have had astromical birth rates over a very short time (and at an age where most women have declining fertility) for the Great Recession to explain the change.

We can check more directly by looking at the age-specific birthrates from the Census Bureau from 2008 to 2014, but in this case I think it very unlikely that births to women in their late thirties accounted for most of the change.

On the other hand, it is quite possible that births to women over 30 accounted for most of the change and that might have been facilitated by reproductive technology, as per Bitsy's second hypothesis.

You know, somebody should call up the data and check the JKR-Bitsy hypotheses. At what age did postgrad-educated women born in 1970-74 start having children at higher rates than women born in 1950-54?

Googling, it looks like about 60,000 babies per year are born in the US thanks to IVF. That's more than I would have expected, but it's still only about 1.5% of the total ~4 million American babies per year.

Upon further googling, it appears the CDC claims that 11% of all American women have sought treatment for infertility at some point. That is /way/ higher than I would have expected, but digging a bit it appears that "sought treatment" is being defined broadly here, possibly including all women who ask their doctors for advice whether they go on to actually have treatments or not.

The overall success rate of fertility treatments seems to be around 60%. So even if all the women who "sought treatment" went on to make a serious attempt to have kids via fertility treatments -- IVF, DI, fertility drugs, what have you -- that's only about 7% more women having kids.

Of course, that's 7% of *all* women. Since about 20% of American women don't have children, 7% of all women = about a 9% increase in the number of childbearing women. So assuming successful fertility treatments result in an average family size as opposed to one kid and done -- a big assumption, but I've already spent about fifteen minutes googling stuff -- then fertility tech is increasing the size of each year's birth cohort by at most about 9%. Put another way, about every twelfth kid in an an average US kindergarten or preschool would be there because of fertility treatments.

That's not trivial! But OTOH it's not enough to be the answer here.

Doug M.

On the other hand, if IVF is disproportionately concentrated among highly-educated women, then it could be a big part of the explanation for the massive shift in that group ... which forms only 13.8% of the 1970-74 birth cohort. No?

Just saw this -- I was looking for a reason why a mutual acquaintance might argue Newfoundland fish were analogous to Greek money, scrolling through the back issues. Alas, I remain unenlightened.

I think factors in the decision to remain childless for one's life have changed. What they are materially, I don't know. Costs of child-raising certainly haven't dropped; neither have incomes for post-graduate women particularly risen; and as you've worked out, IVF just isn't numerically large enough.

On the other hand, I think it wouldn't take much difference in how people evaluate the metaphorical discount rate of future children to account for the shift. I think I've mentioned in email the crazy people in Boston who equate the lives of future individuals to present ones? They might be the statistical tail of a broader trend.

I think I've mentioned in email the crazy people in Boston who equate the lives of future individuals to present ones?

Eh? I don't think I've seen this one...link?

For post-grads, I'd be willing to bet it's [rising relative returns to education] + [assortative mating] + [more burden sharing].

- The costs of child-rearing haven't dropped, but the relative ability of post-grad households to cover them surely have. Lower UE, more earning power on average.

- That earning power also tends to get concentrated by virtue of assortative mating. I'd be willing to bet that most households with a woman with a post-grad degree will also feature a man with at least a bachelors.

- Surveys indicate that burden sharing in child-rearing has become a bigger deal for women as their ability to earn a living on their own has increased. But the scope for burden-sharing is limited in the un- or under-educated tier. High UE, residual machismo, etc. Higher up the food chain, at the extreme you either get a Leeman Kessler willing to play "Mr. Mom" (and quite successfully, FWICT) or you get enough income that the couple can afford higher-end child-care.

I'm late back to the party here, but Bernard has an interesting hypothesis. Might more assortive mating explain the rise?

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