Too Many Pesticides in the Water at the Indiana University School of Medicine?

The media has been abuzz lately over a new research paper by Dr. Paul Winchester of the Indiana University School of Medicine. It purports to find that babies conceived between June and August in Indiana perform worse on standardized tests.

I can believe that this conclusion might be true. Fifteen years ago, economists Josh Angrist and Alan Krueger found that the quarter of birth mattered for school performance, and we’ve written a New York Times column noting that birth-month effects are evident in the composition of World Cup soccer and professional hockey players (presumably because of age cutoffs when they’re children — the ones who just make the cutoff are the oldest and strongest, get the most playing time, and invest the most in getting good at the sport).

I haven’t actually read the new paper by Winchester et al. (I searched but couldn’t find a copy online; the paper is being presented May 7, so I suspect it’s not yet available on the Internet). Still, despite not having read it, I would be willing to bet a whole lot of money that the explanation they give for the test score gap is not correct. Quoting the press release:

Why might children conceived in June through August have the lowest ISTEP scores? “The fetal brain begins developing soon after conception. The pesticides we use to control pests in fields and our homes and the nitrates we use to fertilize crops and even our lawns are at their highest level in the summer,” said Dr. Winchester, who also directs Newborn Intensive Care Services at St. Francis Hospital in Indianapolis.

“Exposure to pesticides and nitrates can alter the hormonal milieu of the pregnant mother and the developing fetal brain,” said Dr. Winchester. “While our findings do not represent absolute proof that pesticides and nitrates contribute to lower ISTEP scores, they strongly support such a hypothesis.”

Pesticides? How many pregnant moms in Indiana are actively exposed to pesticides? I would be shocked if more than 5% of Indiana residents live or work on a farm. Maybe pesticides seep into the groundwater, but how seasonal are the levels? I would think the pesticides would only gradually make their way through the soil into wells or reservoirs.

Still, maybe I shouldn’t be so skeptical. After all, the press release goes on to say the following:

“I believe this work may lay the foundation for some of the most important basic and clinical research and public health initiatives of our time. To recognize that what we put into our environment has potential pandemic effects on pregnancy outcome and possibly on child development is a momentous observation, which hopefully will help transform the way humanity cares for its world,” said James Lemons, M.D., Hugh McK. Landon Professor of Pediatrics at the IU School of Medicine. Dr. Lemons is director of the section of neonatal-perinatal medicine at the IU School of Medicine and at Riley Hospital for Children of Clarian Health in Indianapolis.

I am not one to dismiss surprising and innovative theories out of hand. There are ways that one could make a compelling case for the pesticides argument. For instance, by comparing people in areas heavily affected by pesticides to those who are not. Or by examining two areas over time, one that dramatically reduces pesticides and another that does not. Or by actually measuring pesticide exposure on an individual basis. Or by examining those who move to the region from areas where there are no pesticides.

My guess is that this paper did none of these. My guess is that this paper documents a correlation — probably a weak one — and then simply asserts a causal pathway. A more likely explanation is that these kids conceived between June and August are relatively young for their grades (there is evidence that being young for your grade adversely affects your test scores).

We’ll have to wait and see what the paper says. Regardless, in stark contrast to the quality of reporting by Alan Schwarz on the research on discrimination by NBA referees, the way the press has blindly reported on this study is not the right way to cover science.


Ok, clearly the June thru August babies are the youngest in school and have some disadvantage.

But what about Dr. Winchester? He's a doctor. He's gone to school a whole lot. Has lots of degrees.

What's his excuse?


One major research study I would like to see funded do is a large scale multiple country (US, UK, Australia, Japan, Europe, South America) study for possible causal relationships between chemicals in the environment and diseases.

With a particular focus on food additives, cosmetics and hormones such as oestrogen. Its pure speculation, but I have wondered for a while whether the rise in certain diseases (austism comes to mind but ADHD as well) could show a correlation with the rise in the environmental concentration of these chemicals.

At the very least, the study would be useful for eliminating possible casual links.


"A more likely explanation is that these kids conceived between June and August are relatively young for their grades (there is evidence that being young for your grade adversely affects your test scores)."

Hey Doc, I have been 2 years younger than my grade since middle school. I'd say my test scores have been pretty good. Maybe I'm resistant to the effects of pesticide/youth?


See my latest Huffington Post blog on this very same topic, "The Season of Misconception," at:


I have an alternate theory. Could it be that higher scoring parents (and thus their children) are more likely to plan a pregnancy to avoid a summer birth? Being in the last trimester in the summer months I could imagine is much hotter and more uncomfortable than other months. This was the first thought that came to my mind when reading this, since I know my wife wants to avoid the above predicament.

This would mean that there would also be less total births in the summer - I don't know if this is true or not.


"A more likely explanation is that these kids conceived between June and August are relatively young for their grades"

The above kids would be born from March thru May. Most states (some have earlier cutoff dates) allow kids born up to December 31 to start school the calendar year in which they turn 5.

If one allows for parental "redshirting" of kids born late in the calendar year, November 1 on, kids conceived between June and August would be younger than a third of their classmates (those born November - December of the prior year & those born in January - February) and older than five-twelths of their classmates. I do not think that makes the kids conceived between June and August relatively young for their grades.

Also, how does the performance of kids conceived September to March (assuming those born in February - March not "red-shirted") compare to those conceived June and August?

Please revisit this topic after you have had a chance to review the underlying paper.

I am a big Freakonomics fan, have recommended your book to many, & enjoy your blog.

Lastly, what are your thoughts on revising the AMT to refocus on the reason it was originally passed - to ensure well-paid individuals cannot avoid paying taxes?



lol, i completely misread the article... nevermind


Two quick observations, not commenting about the paper until I have read it. The first is that a number of studies have shown that environmental concentrations of pesticides are actually seasonal and are at their highest in August and September, since they tend to build up all year until harvesting is done. (I know the Ohio State Ag college has done work on this.) Also, pesticides and fertilizers from agricultural runoff are pretty widely distributed through the environment, so the 5% guess is at least an order of magnitude low.

This does not mean that a causal link exists, it just undercuts Dr. Levitt's counter argument. Once again, I don't want to comment on the paper's conclusions and data until reading it.

But I don't mind offering another observation. It has been pretty well documents that people born in October in the northern hemisphere (April in the southern) live longer than other people. September is next. Then August and November. The fairly well but not completely tested theory about this is that third trimester diet for mothers contains the most fruit and vegetables in August - Sept - October. The lowest is March - April - May. It may well be that these scientists have accounted for this in their study, so I don't want to offer it as an alternative explanation, just an observation.



I think this is an interesting sociological phenomenon - science trolling by muckrakers. Like fast food, this reporting is simplistic, processed and meant for indulgence consumption. But because "research" still has (though won't for long)the power of authority people give it more credence than other fiction - though we're really talking about the reprocessing of research into garbage news.
Mass delusion is such a fascinating cultural phenomenon. One could write a book about the dynamics of the process by which a theory or scientific study is transformed into conventional wisdom as it wicks it's way through societal institutions to become something far removed from it's source.


I would be interested in understanding how this effects adulthood. Children aren't children for long, after all.

Are summer month/pesticide children more or less likely than other children, with the same test scores, to have higher divorce rates, lower job stability and growth, lower income or even to drive slow in the fast lane.

Now that I am over 40 I rarely reference my old grade school test scores - my benchmarks have changed a bit.


There is so much going on in summer that is different from other months; I don't think it's realistic to put this down to pesticides alone. It could be diet (burnt hot dogs anyone?), solar radiation, dehydration, lack of exercise or sunlight later in pregnancy (ie, during winter months), or any combination of these and dozens of other factors.

That said, I understand that pesticides (particularly herbicides) are used in most cities during the summer months to keep weeds down on sidewalks and in parks, and many people who have lawns will treat them as well. There would certainly be increased exposure to things like ant-killing sprays, wasp nest treatments, and bug spray - all of which could be considered pesticides, of a sort, if not widely-used industrial agricultural ones. I'd be surprised if they didn't have some effect on humans, but reserve judgement on how significant this effect is when compared to all the other things that can interfere with human development.



It would surprise me if you were right about this one. Most of Indiana is downwind from a farm and much of the state is downstream from one as well. In addition, it's common in suburban neighborhoods to treat lawns with a pest control/fertilizer blend in high enough concentrations to kill pets and sicken children. In short, your assumption that exposure to pesticides (in Indiana) requires living or working on a farm (in Indiana) is false, and so your subsequent conclusions are probably wrong as well.


an informational note: i grew up in indiana and our school system had the birth month cutoff in August (if born in Aug, you had the choice of which school year to go into). So Levitt's counter-proposal could have legs -- Jun-Jul children were certainly the youngest in each cohort where Aug was split either oldest or youngest, depending on parental choice.

Maybe a good check on the data would be to compare Sep kids to May kids (Sep being the oldest group in Indiana and May pretty young, with any pesticide effect likely controlled)


We seem to have a reading comprehension problem here: babies *conceived* between July and September are *born* between March and May, as joewehr said.

And more particularly, we have the reading comprehension problem of not actually having the article to read - reading test scores drop significantly when subjects speculate on the content of articles from their summaries.

All things considered, the amount of randomness that might affect such loosely coupled events as conception date and test scores indicates that either a massive amount of data was reduced or that the conclusions are crap.


Oops, you're right pparkman.

I will go with your last paragraph and still raise you my last question.


I think the best quote is by that James Lemmons fellow. You'd think the guy had cured cancer.

I believe this work may lay the foundation for some of the most important basic and clinical research and public health initiatives of our time

That should get some more funding, eh?


Wait pparkman, Indiana was using June 1 as the deadline and only recently in 2006 changed the admission deadline to August 1.

So perhaps the obvious reason holds?


Reading the comments it seems to me that states in the Midwest have early cutoff dates for starting school compared to at least the Northeast (I live in CT and Dec 31 is the cutoff). How did that come about? What were the reasons and are they still valid? Given the state of our K-12 education performance, maybe that merits funding!


>"the way the press has blindly reported on this study is not the right way to cover science."

The way the authors speculate in the press without making the study available for checking is not the right way to DO science.


The way the authors speculate in the press without making the study available for checking is not the right way to DO science.

Man, you are not aware of just how cocksure these Freakonomics dudes are. These are data Freakoids who know just how hard it is to get enough quality data to tease out even the most obvious correlations. How hard it is to "do good science" as Levitt is wont to say. Much less make broad conclusions about the causes of the correlations.

Levitt's brain is so quick on the data implications of such a "discovery" that that part just bore's him. Instead he immediately finds the fun in the chase to hunt down the fellow's a-bridge-too-far conclusions and to blow them sky high with the scathing verbage of this blog.

It's like telling a skeptic that you saw someone walking on water. When the laughter dies down. What is left?