Regression to the Mean: What to Expect Next Time

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Next time

The average

This result

Repeatability r 0 = pure luck, 1 = repeats exactly

A league of equally good players

Players

Games each a season

Chance of winning each game %

Look at the top

Enter your numbers, then press Calculate.

From the book, Chapter 11. Average 100, a result of 130, repeatability 0.6: best guess next time 118, so 12 points are expected back; a result of 70 points to 82. 100 equally good players, 20 coin-flip games each: last season’s top ten averaged 13.8 wins, and next season they’re expected to average 10.

Exact arithmetic, worked the way the book shows. Everything stays in your browser: no sign-up, nothing stored or sent.