US coal production

It turns out that as Americans dig less coal from the ground, mail carriers get bitten by dogs at almost precisely the same rate of decline, which suggests either that coal dust has been protecting postal workers from canine aggression all along, or that we have simply discovered the universe's most elaborate prank at the expense of pattern-seeking humans like ourselves. The correlation sits at 0.905, which is the kind of number that makes statisticians weep into their spreadsheets.

The actual culprit is almost certainly the economy itself, that great invisible hand that touches everything and occasionally bites. Coal production tends to follow broader industrial cycles and energy demand, which rises and falls with overall economic activity. Meanwhile, mail volume — and therefore the number of hours postal workers spend at people's doors — fluctuates with the same economic tides. Fewer packages during a slowdown means fewer encounters with dogs, fewer dog encounters mean fewer bites, and both trends slope downward together. Between 2016 and 2022, the US shipped roughly 150 billion packages, and somewhere in that vast churn of cardboard and canine anxiety, two completely unrelated industries accidentally synchronised their decline.

We are a species that will find a dance partner in any two columns of numbers, and this correlation is neither the first nor the last time we will stand in amazed confusion before a relationship that explains nothing about itself. The real lesson here is not about coal or dogs, but about the fact that the world is so densely connected that chaos and order are probably indistinguishable. Perhaps they always were.