The U.S. birth rate and WeChat's monthly active users have, between 2016 and 2024, moved in near-perfect opposite directions at a correlation of -0.984. One of them is a quiet American slide from about 12 births per thousand to under 11. The other is a Chinese super-app climbing from 850 million users to over 1.3 billion. They are not, under any sane reading, in the same conversation. The data does not care.
U.S. births per thousand drifted steadily downward as the millennial cohort delayed or declined parenthood, a trend accelerated by rising housing costs, student debt, and pandemic uncertainty. WeChat climbed in parallel because Tencent kept absorbing payments, messaging, mini-programs, and everyday government services into a single app that a substantial fraction of humanity now opens dozens of times a day. Both curves are demographic in the broadest sense, but they describe two entirely different continents and entirely different decisions. The correlation is what happens when any two things changing monotonically are plotted against each other for long enough.
Nine years of two lines moving oppositely can describe two countries doing entirely different things at the same time. Americans had fewer children. A billion people checked WeChat again.
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Want to learn more about why correlations like “WeChat monthly active users” vs “U.S. birth rate” don't prove causation? Read our guide to statistical thinking.
