Tuesday, February 08, 2005

Post Hoc Ergo Propter Hoc
This is unfortunate. If you'll read the article, you'll see its about a study that found an ostensible inverse correlation between multiple daily toothbrushings and obesity. In other words, they found that fat folks brush their teeth less often.

What's so unfortunate about that, you ask? While the merit of undertaking such a study (one wonders what it cost) is debatable, the more pernicious issue to my mind is the way in which the article seems to imply that there is a causative relationship between the two activities. Witness the opening line of the article:
If you want to keep trim, forget the diet books and gym membership -- you may be better off just brushing your teeth more often, according to a Japanese study.
Uh, no. While I haven't read the study, I can say with great confidence that it was not designed to test a causative relationship between obesity and dental hygene. The most likely explaination is obvious: people who care about their physical health will tend to care about their dentition. We needed a study for that?

Of course, the usual suspect in this kind of situation is the journalist. Many journalists, in my experience, have little compunction about writing on topics about which they know little, because hey, they're journalists - they've got their university degrees, eh? It stands to reason, that a less than scientifically fluent journalist might miss the subtle difference between correlation and causation, but egad - here we have a direct quote from the study:
"It's a sign that these people are careful about their health -- they want to maintain the appearance of their teeth and prevent bad breath," the paper said. "We think actively encouraging the habit of toothbrushing would play a role in maintaining health and would help prevent obesity."
It is this same slight of hand that is responsible for other canards such as ETS, the "gateway drug" hypothesis (scroll to middle of page), Erin Brockovich, etc.

posted by Malaclypse the Tertiary at 1:48 PM ·

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Deinonychus Antirrhopus
The Knowledge Problem
The Volokh Conspiracy
The Kolkata Libertarian
Andrew Sullivan
Little Green Footballs
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Libertarian Samizdata
Balloon Juice
Discount Blogger
Truck and Barter
Peking Duck
The Gweilo Diaries

Ludwig von Mises Institute
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Junk Science
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