Math Says Yes

Concept

Regression to the Mean

An extreme measurement is usually a mix of a stable, repeatable part and a one-off lucky part. Because the lucky part rarely shows up the same way twice, the next measurement of the same thing tends to land closer to the average. This is not a force that pulls things toward the middle. It is simply what selecting on luck looks like once you measure again.

Lessons

Dots at the extremes drifting back toward a central average band.

Extremes Drift Back to Average

Record-setting and rock-bottom results usually move toward the average next time, with no cause behind it.

Related Facts

4 min · medium

Front-runners drifting back toward the pack while trailing runners catch up toward the middle.

The best performers usually slip next time

A team's top scorers, a test's top students, and a clinic's sickest patients all tend toward the middle on the next measurement with no intervention at all, because the extreme result was part skill and part luck, and the luck rarely repeats.