How Not to Be Wrong: The Power of Mathematical Thinking

by Jordan Ellenberg

But the Obesity paper conceals a worse crime against mathematics and common sense. Linear regression is easy to do—and once you’ve done one, it’s cake to do more. So Wang and company broke down their data by ethnic group and sex. Black men, for instance, were less likely to be overweight than the average American; and, more important, their rate of overweight was growing only half as quickly. If we superimpose the proportion of overweight black men on the proportion of overweight Americans overall, together with the linear regressions Wang et al. worked out, we get a picture that looks like this. Nice work, black men! Not until 2095 will all of you be overweight. In 2048, only 80% of you will be. See the problem? If all Americans are supposed to be overweight in 2048, where are those one in five future black men without a weight problem supposed to be? Offshore? That basic contradiction goes unmentioned in the paper. It’s the epidemiological equivalent of saying there are −4 grams of water left in the bucket. Zero credit.