Wednesday, May 25, 2011

Pesticides and the Rosenthal effect

There seems to be a rather sad group of people -- mostly on the political Left, apparently -- who are convinced that anything popular is bad. And they go to some lengths to prove it. Hence we have the unrelenting attacks on things as diverse as McDonald's and cellphones. No compromise by McDonald's ever suffices to blunt the attacks and no amount of evidence showing low levels of electromagnetic radiation to be harmless will ever convince. So the attacks go on. And among academics, the attacks take the form of "research".

And pesticides are one of the unexonerable villains for some people. The fact that an upsurge of pesticide use has coincided with an unprecedented expansion of lifespans doesn't cause a moment's doubt.

But this runs us slap bang into the Rosenthal effect: The fact that with the best will in the world, a researcher's expectations will influence what he finds in his research. It is because of that fact that "double-blind" studies are often conducted -- thus leaving as little room as possible for the reseacher to bias his results, wittingly or unwittingly.

So we come to the research report below. It is a very well-designed piece of research. It is far more "watertight" than most other studies in the field. But at least three of the authors are anti-pesticide activists and there appears to have been no effort to make the study "double-blind". That also makes it worthless in my view.
Prenatal Exposure to Organophosphate Pesticides and IQ in 7-Year Old Children

By Maryse F. Bouchard et al.


Context: Organophosphate (OP) pesticides are neurotoxic at high doses. Few studies have examined whether chronic exposure at lower levels could adversely impact children’s cognitive development.

Objective: To examine associations between prenatal and postnatal exposure to OP pesticides and cognitive abilities in school-age children.

Methods: We conducted a birth-cohort study (CHAMACOS) among predominantly Latino farmworker families from an agricultural community in California. We assessed exposure to OP pesticides by measuring dialkyl phosphate (DAP) metabolites in urine collected during pregnancy and from children at age 6 months and 1, 2, 3½ and 5 years. We administered the Wechsler Intelligence Scale for Children-IV to 329 seven-year old children. Analyses were adjusted for maternal education and intelligence, HOME score, and language of cognitive assessment.

Results: Urinary DAP concentrations measured during the 1st and 2nd half of pregnancy had similar relations to cognitive scores, thus we used the average of concentrations measured during pregnancy in further analyses. Averaged maternal DAP concentrations were associated with poorer scores for Working Memory, Processing Speed, Verbal Comprehension, Perceptual Reasoning, and Full Scale IQ. Children in the highest quintile of maternal DAP concentrations had an average deficit of 7.0 IQ-points compared with those in the lowest quintile. However, children’s urinary DAP concentrations were not consistently associated with cognitive scores.

Conclusions: Prenatal but not postnatal urinary DAP concentrations were associated with poorer intellectual development in 7-year-old children. Maternal urinary DAP concentrations in the present study were higher, but nonetheless within the range of levels measured in the general U.S. population.


What a laugh! The old traffic pollution bandwagon rolls again!

An amazingly naive study below. Some researchers into this topic have absorbed the lesson that they must control for social class variables if they are to be taken seriously but the guys below have just reinvented the wheel.

The study is in a "pay to publish" journal so it's what one has to expect, I guess. The journal concerned is also a government one so that is a second reason for expecting poor quality.

The authors found that people who lived near busy roads were dumber. But only dumb people would live near busy roads!
Traffic-Related Air Pollution and Cognitive Function in a Cohort of Older Men

By Melinda C. Power et al.


Background: Traffic-related particles induce oxidative stress and may exert adverse effects on central nervous system function, which could manifest as cognitive impairment.

Objective: We assessed the association between black carbon (BC), a marker of traffic-related air pollution, and cognition in older men.

Methods: A total of 680 men (mean ± SD, 71 ± 7 years of age) from the U.S. Department of Veterans Affairs Normative Aging Study completed a battery of seven cognitive tests at least once between 1996 and 2007. We assessed long-term exposure to traffic-related air pollution using a validated spatiotemporal land-use regression model for BC.

Results: The association between BC and cognition was nonlinear, and we log-transformed BC estimates for all analyses [ln(BC)]. In a multivariable-adjusted model, for each doubling in BC on the natural scale, the odds of having a Mini-Mental State Examination (MMSE) score ≤ 25 was 1.3 times higher [95% confidence interval (CI), 1.1 to 1.6]. In a multivariable-adjusted model for global cognitive function, which combined scores from the remaining six tests, a doubling of BC was associated with a 0.054 SD lower test score (95% CI, –0.103 to –0.006), an effect size similar to that observed with a difference in age of 1.9 years in our data. We found no evidence of heterogeneity by cognitive test. In sensitivity analyses adjusting for past lead exposure, the association with MMSE scores was similar (odds ratio = 1.3; 95% CI, 1.1 to 1.7), but the association with global cognition was somewhat attenuated (–0.038 per doubling in BC; 95% CI, –0.089 to 0.012).

Conclusions: Ambient traffic-related air pollution was associated with decreased cognitive function in older men.


There was actually something interesting in their data which they promptly "ironed out": The relationship was non-linear. That may suggest that a medium level of proximity to busy roads was beneficial to IQ! They actually did have something interesting to report but were too fixed onto their mental train-tracks to see it! They threw out the baby and kept the afterbirth. And the three leading researchers are from Harvard!

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