Study Finds High Exposure to Dioxin Increases Cancer Riskreported the Associated Press on May 5, 1999. The article continued:
"Chemical workers exposed to high levels of dioxin have a 60 percent
increased chance of dying of cancer, but the chemical poses no added cancer
risk to the general population, a study says. Kyle Steenland, co-author
of the study appearing today in the Journal of the National Cancer Institute,
said the research suggests most people typically are not exposed to dangerous
levels of dioxin and that cancer appears to result only among those who
had extremely high and long-term exposures to the chemical 15 to 20 years
The researcher's conclusion is based on a pooling of the weak statistical
associations for specific cancers into a category called "all cancers."
Check out the study's results for "all cancers" and specific cancer
sites in Table 11.1
You'll notice that other than the statistical associations for bladder and larynx cancers, none of the reported statistical associations is statistically significant by virtue of its confidence intervals. (We don't know about the p-values because they weren't reported—or do we?)
The researchers try to circumvent this problem by combining data for the specific cancer sites into an "all cancer" category. But as Bruce Charlton pointed out earlier:
"The root of most instances of statistical malpractice is the breaking of mathematical neutrality and the introduction of causal assumptions into the analysis without scientific grounds. This amounts to performing science by sleight-of-hand: the quickness of statistics deceives the mind."
In this case, the researchers assumed that it was biologically possible
for dioxin to be a cancer-causing agent at all sites in the body—even though
there is really no persuasive evidence that it acts as a cancer-causing
agent even at one site. The "all cancers" category is a statistical trick
to enable the conclusion that dioxin is a cancer-causing substance.
A general rule that may be taken from the "all cancers" trick is, in epidemiologic studies, beware of statistical pooling intended to overcome data that provide the "wrong" answer.
Note from RJB--Two out of 19 tests are significantly different from 1 at the 5% level, according to the confidence limits shown. The probability of this occurring by chance, according to our studies on sampling statistics and the Central Limit Theorem, is almost 20%. Pooling of all the data gave a larger sample size, but one could question whether this is legitimate. Five of the categories give results, albeit insignificant, “suggesting” a protective effect of dioxin (relative risk<1), and even with pooling, the relative cancer risk from high level exposure to dioxin is barely significant at the 5% level. Moreover, who knows what other characteristics the subjects might have had in common?
Dioxins are a family of some 75 compounds that occur naturally from a number of processes, including forest fires. There is some evidence that higher levels resulting from human activities may be detrimental to human health. Do a google search to see some of the controversy. Here is a good overview: http://www.heartland.org/Article.cfm?artId=12374
Ben & Jerry assert in a brochure that "the only safe level of dioxin
is zero," which is impossible to achieve. Michael Gough and Steven
Milloy actually had dioxin levels in Ben & Jerry’s ice cream measured
by two independent labs and found one serving gave a dioxin exposure 200
times the “EPA safe level.” Nobody has questioned the findings. Instead,
various environmental groups have subjected Milloy to bitter personal attacks
for being "pro-industry."
here are a few references:
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