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.