Kudos to Kent Sepkowitz for his very smart piece in yesterday s Daily Beast. The title alone Today s ADHD Blame Game: Pesticides suggest critical thinking about chemical toxicity something that is very rare in these days of one phony scare after another is being applied. Indeed Sepkowitz uses just that, and does so brilliantly.
In addition to debunking the obviously flawed theory of ADHD having anything to do with a very safe type of pesticide, he also demonstrates beautifully how phony chemical scares arise: through faulty logic, bad data, and the general lack of understanding of even the most fundamental knowledge of epidemiology especially as it pertains to cause and effect, and disease.
Sepkowitz picked the perfect example of how to be spectacularly unsuccessful in doing good science, but quite the opposite in spreading it around. He examined a study in the Environmental Health a journal best suited for the bottom of a bird cage, and one we have criticized in the past.
The study entitled Association of pyrethroid pesticide exposure with attention-deficit/hyperactivity disorder in a nationally representative sample of U.S. children, tries to establish a correlation between ADHD and exposure to bug spray. Then they suggest, although not directly, that the correlation is more than that a cause and effect.
ACSH s Dr. Josh Bloom explains, Correlations can be real or coincidental. It is not always easy to tell, but in general, if an observational study (using data from past studies) does not show a large effect, there probably isn t even a real correlation. Cause and effect requires much more stringent criteria and very good data. This study doesn t even meet the first criterion, which automatically precludes the second.
Sepkowitz hits the ground running as he discusses the difference between what the study authors would have you believe, and the reality of it.
The premise of the study is that kids with detectable levels of pyrethroid pesticides in their urine on the surface seem to have more ADHD. He says, [The study authors] found that kids with detectable pyrethroid were twice as likely to have ADHD as kids without; furthermore, and perhaps more convincing, the higher the level of pyrethroid, the greater the likelihood of ADHD. That clinches it, right? Of course not. Simple things are never simple and ADHD is nothing if not incredibly dense.
He proposes a few ridiculously idiotic (funny, actually) scenarios that could explain the study findings: Perhaps [people with AHDH] are really, really afraid of bugs, and cope by obsessively spraying and calling Orkin twice a month to boot. Maybe such bug-o-phobia is more common in people with ADHD or their parents. Maybe people with ADHD are more likely to lick sprayed surfaces as part of the overall collection of symptoms that constitutes ADHD. Maybe, maybe, maybe.
While Sepkowitz points out the impossibility a straightforward explanation from a very flawed study, Dr. Bloom easily noted the actually flaws.
He explains, To name a few: 1) It is a retrospective study that looked a kids for a period of one year; 2) The diagnosis of ADHD is rather subjective, and was determined by two different methods; 3) A positive result for the presence of the pesticide was considered to be whether it could be detected at all. This is utterly meaningless enough so to disqualify the study singlehandedly; 4) The magnitude of the effect was small; 5) It was seen in boys, but not girls. I could go on.
The conclusion from the study: Given the growing use of pyrethroid pesticides, these results may be of considerable public health import.
Dr. Bloom has a two word response to this. One of them is bull.