Truthiness with Numbers

By George Johnson | February 22, 2013 12:39 pm

Yesterday on Collide-a-scape, Keith Kloor, writing about climate change deniers and opponents of genetically modified food, used a nice turn of phrase: “veneer of science.” Positions that are rooted in politics or gut-level emotions are dressed up by citing and often distorting isolated studies, ignoring that in science what counts is the body of research, the preponderance of evidence.

That perfectly describes what is happening with the fluoride debate. There is nothing crazy about thinking that high levels of fluoride can be harmful. Fluorosis of the teeth is the one risk that has been established. For excessive exposure over the course of many years, there is disputed evidence of the possibility of a weakening of bones in adults. Any other effects are even more controversial and fall into the netherworld of epidemiological correlations that may be nothing more than statistical flukes. They become a worry when naturally occurring fluoride exceeds the EPA standard of 4 parts per million, a rarity in the United States. When that happens, regulators call for fluoride to be filtered from the water. A study published in 2006 by the National Academy of Sciences recommended a more conservative limit of no more than 2 parts per million. Judging by the numbers in the report, far less than 1 percent of the population is exposed to that much.

Again, as Paracelsus put it, the dose makes the poison. But the anti-fluoride activists blur over the distinction. They use the academy’s study to argue against the recommended (not mandated) practice of reducing tooth decay by bringing water with barely measurable amounts of fluoride up to a threshold — judged harmless by the preponderance of evidence — of 0.7 parts per million.

More recently the extremists have embraced a study published last year about the possibility of neurological effects from chronically high fluoride contamination. Developmental Fluoride Neurotoxicity, a collaboration of the Harvard School of Public Health and China Medical University, looked at 25 epidemiological studies from China and two from Iran. The smallest involved 20 subjects, the largest just over 300.

“Each of the articles reviewed,” the authors observed, “had deficiencies, in some cases rather serious ones, that limit the conclusions that can be drawn.” They noted that “the studies were generally of insufficient quality.” They were done by various researchers between 1989 and 2011 “according to the standards of science at the time.”

In each study — involving communities with seriously tainted water or where people burned coal, high in fluoride, inside their homes — there were indications that the children had IQs a few points lower than for the control groups. Confounding factors, like the possibility of lead and other contaminants, were not considered.

Seven different methods had been used to measure I.Q. — the Wechsler Intelligence Scale, Chinese Standardized Raven Test, Chinese Binet Test, Japan test . . . and another just called “Child mental work capacity.” Fluoride was also measured in various ways: milligrams per liter (of water or excreted urine), milligrams per kilogram of coal, percentage of children with dental fluorosis. Three studies didn’t give measurements, only distinguishing between high and low fluoride areas.

Taking the uncertainties and imperfections into account, the epidemiologists combined the data in a meta-analysis and concluded, with all the appropriate qualifications, that “the results support the possibility of an adverse effect of high fluoride exposure on children’s neurodevelopment.” (I’m adding the italics since this distinction is so stubbornly overlooked.) They called for further research.

Inquiring reporters received the following caveat:

“These results do not allow us to make any judgment regarding possible levels of risk at levels of exposure typical for water fluoridation in the U.S. On the other hand, neither can it be concluded that no risk is present.”

Which is the problem with all of these issues: you can never prove a negative. And that opens the door for truthiness with numbers. Scienciness.

__________

This is part 3 of three posts:

Fluoride Paranoia and Betteridge’s Law

Fluoride Paranoia, Part 2

Truthiness with Numbers

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Fire in the Mind

Whether a subtle new pattern shows up in an experiment on the Higgs boson, an epidemiological report about a suspected cancer cluster, or a double-blind trial purporting to demonstrate ESP, it can be maddeningly difficult to distinguish between what we see and what we think we see. "Fire in the Mind" takes a look at the big questions behind today’s science news.

About George Johnson

George Johnson writes about science for the New York Times, National Geographic Magazine, Slate, and other publications. His nine books include The Cancer Chronicles: Unlocking Medicine's Deepest Mystery (August 2013), The Ten Most Beautiful Experiments, A Shortcut Through Time, and Fire in the Mind. He is a winner of the AAAS Science Journalism Award and has twice been a finalist for the Royal Society science book prize. Co-founder and director of the Santa Fe Science Writing Workshop, he can be found on the Web at talaya.net. Twitter @byGeorgeJohnson.

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