Simpson’s Paradox

When the totals lie

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• A trend in every group can reverse in the combined data: Simpson’s paradox.
• It happens when group sizes and baseline rates differ, usually because of a confounder.
• Always ask what else differs between the groups you’re comparing.

Steps

1. Kidney stones
2. Which is better?
3. Simpson’s paradox
4. Berkeley, 1973
5. Make the reversal happen
6. Batting averages