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.