Key ideas

• Every performance reflects both stable factors, like skill, and temporary factors, like fatigue, confidence, and chance.
• An unusually great or poor performance often happens when temporary factors happen to line up for or against the person, and they are unlikely to line up the same way next time (e.g., a player who usually makes half his free throws going 10 for 10).
• Because of regression toward the mean, psychologists are cautious about drawing conclusions from a single unusually good or bad result.
• When participants are chosen for extreme scores, a control group shows how much change is just regression; only the extra improvement in the experimental group can be credited to the treatment.

Key terms

regression toward the mean

The tendency for unusually extreme performances to be followed by performances closer to that individual's typical performance.

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