|
medpundit |
||
 |
 |
|
Thursday, April 17, 2003Canfield and Lanphear's team studied 172 children in the Rochester, N.Y., area, measuring blood lead levels at ages 6, 12, 18, 24, 36, 48 and 60 months. The children were tested for IQ at both 3 and 5 years of age. They found that a rise in lead levels from 1 mcg/dl to 10 was associated with a 7.4-point drop in IQ. An increase in lead levels from 10 to 30 mcg/dl was associated with an additional drop of only about two to three IQ points, in line with previous studies.... "People have been asking, `How low (a lead concentration) is low enough?"' said Dr. Richard Canfield of Cornell University, one of the leaders of the study. "The fact is, in our study, we found no evidence for a safe level. There is no safe level of exposure." The study shows no such thing. The researchers used the Stanford-Binet IQ test to assess the intelligence of three and five year olds. The test, although designed to be used from age two on up, is less accurate in preschool children. But, even more damning are the data themselves. The paper includes a graph (subscription required) of IQ’s against lead levels. The distribution is by no means linear, especially at lead levels less than 10 micrograms/deciliter, the current cut off for lead toxicity. IQ’s at the lowest levels of lead exposure (i.e. under 10micrograms/dl) range from the high 60’s to around 130, with a very widely dispersed distribution of plotted points between. Children with lead levels higher than ten, however, have a much narrower spread of IQ values. The plotted data points for levels below 10 micrograms/dl look more like a globule than a line. Looking at the graph, it’s clear that there’s no association between low lead levels and IQ. But, the researchers use averages to condense it into a nice downward sloping line to prove their hypothesis. It’s a shameful misuse of statistics, especially when you consider that the estimated cost of making all houses absolutely lead free is $32 billion. posted by Sydney on 4/17/2003 07:44:00 AM 0 comments 0 Comments: |
|
