IQ, pesticides, special ed: LATimes article misses fundamental points of human study designs.

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http://www.environmentalhealthnews.org/ehs/blog/los-angeles-times-misses-feature\

s-of-pesticide-study-design

Article misses fundamental points of human study designs.

Posted by Volk at Apr 28, 2011 07:00 AM

The Los Angeles Times misinterprets four key aspects of studies that

find a mother's pesticide exposures during pregnancy can affect the

child's intelligence.

/Posted by Joe Braun and Volk/

A recent Los Angeles Times article

<http://articles.latimes.com/2011/apr/21/news/la-heb-pesticide-children-20110421\

>by

Marissa Cavallos described three new studies reporting that pesticide

exposure during pregnancy may be associated with lower IQ in children.

The three studies -- conducted in New York City and Salinas, Calif. --

measured pesticides in pregnant women and followed their children for up

to nine years. They found that children born to pregnant women with

higher pesticide concentrations had lower IQ scores.

Cavallos misses four important features of these studies: 1) effects of

small IQ shifts, 2) pesticide exposure measures 3) sources of pesticide

exposure and 4) consistency across studies.

First, she underestimates the effects of small IQ shifts. She states

that the pesticides are " slightly " harmful and that the 1 to 7 point

drop in IQ found in the studies was " small. " For an individual, these

changes may not be substantial. However, these are not trivial changes

in a population where small shifts in the mean IQ can have substantial

effects on the number of children who need special education.

Imagine two populations of one million children each. One population has

a mean IQ of 100. At the high and low ends of the distribution -- called

the tails -- about 23,000 people at the high end would be called gifted

(IQ greater than 130) and 23,000 people at the low end would be

intellectually disabled (IQ less than 70). In the other population the

mean IQ is 98 -- now 16,000 would be gifted and 31,000 would be

intellectually disabled. Even if pesticide exposure is only associated

with a two-point drop in IQ, that population would have thousands fewer

gifted and highly productive children and thousands more intellectually

disabled children who require additional resources for education. These

" slight " decreases in IQ can have profound effects on the education and

livelihoods of children.

Second...

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