What Drives Obesity? An Economist Takedown of The Economist

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Is higher obesity due to the rise in driving? Perhaps. It’s an intriguing hypothesis. But our friends at The Economist should know better than to report nonsensical correlations. Here’s the evidence they cite (drawn from this entirely unconvincing research paper published in Transport Policy):

Looks impressive, right?  (Well, apart from putting the explanatory variable on the vertical axis.) But before concluding that there’s anything here, let’s try a different variable, instead—my age:

Unlike the authors of the original paper, I didn’t even need to fiddle with the lag structure to get such a good fit, nor test alternative definitions of the variable. In fact, my variable fits even better than vehicle miles traveled.

Okay, I’m not arguing that my aging is causing higher obesity. Rather, when you see a variable that follows a simple trend, almost any other trending variable will fit it: miles driven, my age, the Canadian population, total deaths, food prices, cumulative rainfall, whatever.

Sure, The Economist offered the usual caveat that “correlation does not equal causation.” But this is so completely unconvincing as to warrant a different warning: “Not persuasive enough that you should bother reading this article.” I’m not saying the relationship doesn’t exist, simply that it makes more sense to highlight more persuasive research on this question.

P.S.: How cool is Stata’s “Economist” scheme? It lets stat-nerds like me replicate magazine-quality art.

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  1. Mike H says:

    Clearly, as people get fatter, it causes you to age. You should encourage everyone to diet and exercise, so you can live forever.

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  2. Joe says:

    In order to ascertain if Mr. Wolfers’ existence is the root cause of obesity in the US, I propose that he perform an experiment . . .

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  3. Confounding says:

    This is sadly not the first time this has happened in The Economist. I detailed one of their other mishaps here: http://confounding.net/2009/10/21/next-on-when-graphs-attack/

    It’s gotten to the point that I start automatically rethinking their graphs the moment I see them.

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  4. Michael says:

    It is almost certainly different in different regions. Englishmen who go to live in Scotland usually put on weight because there is a much higher availability of fatty food and it’s cold, but not so cold that proper clothing is a survival matter. Put the two together and you can not feel so cold by eating the readily available fats.

    Then you spend years looking for a way to lose it. But I’m getting there.

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  5. beef says:

    The miles driven stat is a proxy for a basket of life style choices. This stats implicitly represents many degrees of freedom in the analysis. It makes a suburban lifestyle (drive everywhere) endogenous to the argument. It kind of flippant to dismiss all value in this using ‘correlation != causality’.
    The Economist is hardly known for lack of editorial oversight, you might not like some of their conclusions and they are often proven wrong in the long run, but they rarely would publish something as simplistic as you posit.

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  6. aitch555 says:

    Huff on How to lie with Statistics showed STDs and consumption of coke were highly correlated for Vietnam…additional confounding variable was presence of US troops!

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