That the federal prison population should track typewriter sales is precisely the sort of correlation the universe serves to remind you that patterns are everywhere and meaning is nowhere. One imagines a room full of inmates and a room full of hobbyists, both clattering away at machines nobody uses anymore. Click.
Typewriter sales have been in long-term decline for obvious reasons, with a small hobbyist revival occasionally poking the curve upward, while the federal prison population fell sharply in 2020 as covid early-release programs emptied overcrowded facilities to reduce outbreaks. Neither trend is caused by the other, and the lines only rhyme because both took particularly steep turns in the same pandemic year. The common variable is the calendar, not the keyboard.
So the correlation is the accidental harmony of two unrelated declines. Machines and cellblocks, both less crowded. The keys went quiet at roughly the same time.
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Want to learn more about why correlations like “Typewriters sold” vs “US federal prison population” don't prove causation? Read our guide to statistical thinking.