Lesson · 4 min Gentle

Correlation and Causation

In one line Two things moving together is a clue, not a cause.

Two things can rise and fall together without one causing the other. A correlation is a pattern. A cause is a reason the pattern happens. The pattern is the clue, not the verdict.

Hot weather increases ice cream sales and swimming. Swimming increases drownings. Ice cream and drowning correlate. Banning ice cream would not make the water safer. The third factor, heat, is doing the work.

Before you let a headline say “X causes Y,” ask: which way would the arrow point, what else moved at the same time, and what would the pattern look like if that hidden factor were removed?

Summer numbers

A town board sees ice cream sales and drowning calls climb every July. A sarcastic motion to “restrict cones” would get a laugh because the missing variable is obvious. The same shape of mistake is harder to see when the variables are a new app, a crime statistic, and a year when three other things changed too.

Try this today Take one “X causes Y” headline and name a third factor that could be behind both.