Friday, August 15, 2008

Flawed Logic in Obesity Forecast

“In the future, everyone will be fat — or so warns a news study published online last month in the medical journal Obesity. About 66 percent of American adults are now overweight or obese, according to government estimates, and the report makes the dire prediction that by 2048 the figure will reach 100 percent. But that projection, which presumes a linear increase in the number of people who are overweight, is logically impossible, say several top statisticians. The reasons are outlined in one of my favorite columns, ‘The Numbers Guy,' written by the Wall Street Journal’s Carl Bialik. ‘Employing that same logic, 13 out of every 10 adult Americans by then won’t have landlines,’ Mr. Bialik wrote. ‘The phone forecast is impossible, of course, but it’s arguably no less solidly grounded than the obesity forecast.’ Mr. Bialik also interviewed top statistician Donald Berry, chairman of the department of biostatistics at the University of Texas M.D. Anderson Cancer Center. ‘Extrapolations are dangerous,’ Dr. Berry explained. ‘Especially dangerous is to assume that trends are linear. Otherwise we’d conclude that Olympic swimmers will one day have negative times, there will be more Internet users than people, and more people on Earth than molecules in the universe.’”

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