It turns out that Americans' willingness to buy bulk toilet paper in cathedral-like warehouses correlates almost perfectly with their willingness to die in cars, which is either a devastating indictment of consumer capitalism or the universe's driest joke about supply chains. One went up by roughly 150 billion dollars between 2010 and 2022, the other by several thousand people, and they did it in perfect synchronisation, like a particularly grim dance partner who knows exactly when you're about to step backward. We have somehow tied the great American tradition of purchasing seventeen pounds of almonds to the great American tradition of not paying attention at intersections.
The real culprit is almost certainly economic activity itself, that invisible hand that both opens wallets and apparently relaxes grip on steering wheels. As the economy expanded, more people drove more miles—Costco's revenue grew largely because more of us existed and had disposable income, but that same economic growth meant more vehicles on highways, more commutes, more opportunities for the kind of split-second failures that turn traffic into tragedy. Consider that total vehicle miles driven in America increased by roughly 20 percent over this same period, a number so large and abstract it's almost impossible to picture, except as the equivalent of driving to the sun and back about 200 times, collectively, in one year, with half the drivers checking their phones.
We are pattern-recognition machines who occasionally mistake the shadow cast by a third thing for a relationship between two things, which is either humbling or horrifying depending on your mood. The correlation between Costco's expansion and traffic fatalities tells us almost nothing about either one, but everything about how easily we can mistake movement for meaning. We just really like to see shapes.
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Want to learn more about why correlations like “Costco annual revenue” vs “US traffic fatalities” don't prove causation? Read our guide to statistical thinking.