How Many Baby Boys Did the Clean Air Act Save?

(Brand X Pictures)

Our latest Freakonomics podcast, “Misadventures in Baby-Making,” includes a discussion of how sex-selective abortion has led to 160 million missing females in Asia. Closer to home, however, researchers Nicholas J. Sanders and Charles F. Stoecker are focusing on a different problem: missing baby boys. In an effort to evaluate the effects of environmental policy on fetal health outcomes, the authors examine the “gender ratio of live births.”  From the abstract:

We present the gender ratio of live births as an under-exploited metric of fetal health and apply it to examine the effects of air quality on fetal health. Males are more vulnerable to side effects of maternal stress in utero, and thus are more likely to suffer fetal death due to pollution exposure. We demonstrate this metric in the context of the Clean Air Act Amendments of 1970 (CAAA) which provide a source of exogenous variation in county-level ambient total suspended particulate matter (TSPs).

The authors find surprisingly significant results:

We find a statistically and economically significant association between ambient TSP levels and the fraction of live births that are male: a one unit increase in annual ambient TSP levels is associated with approximately a 0.088 percentage point change in the probability of a live birth being male, and a standard deviation increase in the annual average TSPs (approximately 35 micrograms per cubic meter) is associated with a 3.1 percentage point change. These effects are larger when considering particularly vulnerable subgroups, such as less educated mothers, single mothers, and black children.

We convert this gender ratio change into a potential measure of fetal deaths prevented by the TSP reductions caused by the CAAA. We discuss a number of possible metrics, and estimate a range of 21,000 to 134,000 avoided fetal deaths, or 2 to 13 percent of the birth population in those counties.

That’s a pretty big range, but even the lower-bound is pretty striking: a minimum of 21,000 avoided fetal deaths as a result of the CAAA?  It certainly makes you wonder how many fetal deaths are currently being caused by ongoing air pollution — in the U.S. and elsewhere.

Mike B

This of course assumes that out of control population growth is a good thing. Perhaps fetal deaths from pollution is just a natural feedback mechanism that would help to restore some semblance of balance if left unchecked.


Your post of course assumes that out-of-control abortions are a good thing.

Oh wait, you aren't assuming that, just like the researchers aren't assuming anything, they are just making observations.

Still, polluted air does sound like a cheap way to limit the population of impoverished black males, which should keep the crime rate lower than it might otherwise be, and of course takes a load off the health industry. I mean no anti-pollution legislation has ever saved the nation any money, and obviously poor black women losing male foetuses is the only negative thing that could ever come from this type of pollution (As if pollution really exists!) so really it's a win-win. The only bad thing about this legislation is, yet again, those pesky meddling liberals are taking away good honest jobs from abortion doctors. Damn you socialism!


So eliminating the EPA actually has a cost? But Paul Ryan insists it's just a dispute over "regulation" and that Obama is being "petty" when he says the GOP is pushing for dirtier air.


It would be interesting to know whether the personhood law that is being considered could be used to shut down large polluters using this data. It helps make the argument that "pro-life" activists ought to be more concerned about our energy policy.


The pettyness and sarcasm from the comenters is refreshing, the fact that the third world Africa, as a rule, has no industry and dust is the pollution. So males for everybody? The industrial world has more femailes. My college student son will be happy to hear that.
The study sounds like blarney, and a waste of time and research money!!


Is this article saying 21,000-134,000 deaths prevented yearly by Clean Air Act or totally since it's inception?


This seems like quite a stretch to assume that the only progress that has been made in the last 40 years is Air Pollution!

Over that same period of time I'm sure that there was a declining number of mothers that were smoking while pregnant. I'm sure that there were at least a couple advances in pre-natal care since the 70s. But you know you are probably right its got to be the air thing . . .