I love Carl Bialik’s “Numbers Guy” column in the Wall Street Journal and last week he had another gem, headlined, “Obesity Study Looks Thin.” Excerpt:
In 40 years, every single American could be overweight, according to a recent study. Employing that same logic, 13 out of every 10 adult Americans by then won’t have landlines.
The phone forecast is impossible, of course, but it’s arguably no less solidly grounded than the obesity forecast. The weight projection uses three data points spread out over nearly three decades to estimate a linear trend — then brazenly draws that line into the future.
The result: 86.3% of American adults will be overweight or obese in 2030, compared with 66.3% by the government’s latest estimate. By 2048, the percentage will reach 100%. The study doesn’t go beyond that date, but that upward trend would reach logical impossibility the following year.
“Extrapolations are dangerous,” says Donald Berry, chairman of the department of biostatistics at the University of Texas M.D. Anderson Cancer Center. “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.”
The problems with obesity are bad enough and clear enough. They don’t need a boost from statistical sensationalism.