Giving Bad Weight
Following up on Eric's recent post on obesity statistics: according to a nationwide phone survey, about one quarter of the residents of Oregon, Idaho, and Washington are obese, up from about one in ten in 1990.
Surprisingly, that's the good news.
The bad news is that the survey is flawed -- and the real obesity rate is almost certainly a lot higher.
According to a recent study, people simply don't tell the truth about their height and weight (the two ingredients in the obesity calculation) over the phone. Men tend to report that they're taller than they actually are, while women tend to shave a few pounds off their weight.
I doubt that people are outright lying, really. More likely, it's a combination of embarrassment and wishful thinking. I mean, we all like to think of themselves as taller and slimmer than we actually are. I know I do -- I think of myself as weighing what I did a decade ago. But I don't.
So the end result is that the actual obesity rate is significantly higher -- perhaps 8 or 9 percentage points higher -- than the phone-only data would lead you to believe. (This varies by location, sex, and demographics: apparently, certain groups of people are especially prone to exaggeration. See especially p. 63 of this pdf.)
So that means two things. First, the actual obesity rate in the Northwest US is probably closer to 1 in 3. And second, you should take phone survey data for what it's worth: a useful tool for understanding what's going on in the world, but far from the final word.
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