Math Through Sports
Cause or coincidence?
6 min · Two things moving together does not mean one moved the other.
- Correlation vs causation
The stat
Two things moving together does not mean one moved the other.
Learn the number
Correlation means two measurements tend to move together. Causation means one actually makes the other happen.
Correlation is easy to measure and causation is hard to prove — which is why so many confident sports takes are really just correlations.
Two common traps: a third factor driving both, and the direction being backwards.
Read the stat
A team wins 80% of games when their running back carries 25+ times.
- It sounds like heavy carries cause wins.
- Ask what else is true in those games: teams that are already ahead run the ball to protect a lead and burn clock.
- So being ahead causes the carries at least as much as the carries cause the lead.
- The third factor — game state — drives both numbers.
The correlation is real. The causal story attached to it is probably backwards.
Your turn
Ice-cream sales and drowning deaths rise together every summer. What is the third factor?
Explain what it means
When you see a stat like "the team is 9–1 when X happens", ask what else is true in those ten games before you believe X caused anything.
Make a prediction
Find a "team is undefeated when…" stat this week. Predict whether it holds up next game, and write down the third factor you suspect.
Review what happened
When it breaks, check whether the stat ever described a cause — or just described games the team was already winning.
Check your understanding
0 of 3 correct
Every question has to be right for this lesson to count as complete. Miss one and you can try it again.