What statistical phenomenon causes participants with extremely low pre-test scores to likely score closer to the average on a subsequent test, regardless of intervention?

Answer

Regression to the Mean.

Regression to the Mean describes the tendency for statistical outliers to move toward the average score upon retesting, an effect that a control group helps researchers filter out.

What statistical phenomenon causes participants with extremely low pre-test scores to likely score closer to the average on a subsequent test, regardless of intervention?
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