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EC number: 239-290-0
CAS number: 15245-44-0
This communication addresses recent literature that purports the
existence of a supra-linear dose-response relationship between
environmental measures such as blood lead concentrations and IQ. The
authors found no convincing evidence from animal studies supporting this
relationship. Blood lead concentrations in the general population are
lognormally distributed, whereas raw scores from various IQ tests are
standardized to a normal distribution. The authors demonstrate that a
supra-linear slope is a required outcome of correlations between data
distributions where one is lognormally distributed and the other is
normally distributed. The required supra-linear nature of the IQ-blood
lead relationship will not necessarily change when confounders are
included in the analysis if the confounders themselves are also normally
distributed. The authors conclude, "The analysis shows that caution
should be taken in assigning biological significance to supra-linear
dose-response relationships in these instances. Detailed analyses of
such data sets should be conducted to determine if the magnitude of
supra-linear slopes are more or less than mathematically required, and
from there to consider biological significance."
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