It is a curious fact, and one that probably says something deeply unflattering about the human brain, that as Americans have grown collectively wealthier and more inclined to purchase toilet paper in bulk, bicyclists have died in increasingly consistent numbers. There is something almost mathematically tragic about two completely unrelated phenomena deciding to synchronise perfectly for thirteen years, as though the universe were conducting an orchestra made entirely of spreadsheets. You would think Costco's expansion and cyclist fatalities would occupy entirely different moral universes. Apparently they do not.
The most obvious culprit, were we being honest with ourselves, is simply that both trends ride (as it were) on the back of broader economic and demographic currents. Between 2010 and 2022, the United States population grew by roughly 3.5 percent, the middle class rediscovered the bicycle as both commuting device and lifestyle choice, and Costco expanded from 432 locations to 581—each warehouse roughly the size of five football fields. What we are almost certainly watching is two different reflections of the same underlying growth: more people, more economic activity, more cars, more cyclists, more crashes. Urban cycling increased not because people became more virtuous but because gas prices climbed, bikes became trendy, and population density increased in exactly the places where people ride them.
The real insight here is not that Costco is killing cyclists, but that our pattern-recognition systems are so aggressively enthusiastic they will match absolutely anything to absolutely anything else given enough time and sufficient numerical alignment. Both datasets respond to the same demographic tide; neither causes the other. But knowing this changes almost nothing about how satisfying these 0.969 correlations feel. We are pattern-seeking creatures living in a world full of coincidences masquerading as meaning.
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Want to learn more about why correlations like “Costco annual revenue” vs “Bicyclist traffic fatalities” don't prove causation? Read our guide to statistical thinking.