![[empirical-rule.png|300]] The empirical rule is a theorem for [[Normal Distribution|normal distributions]] stating that approximately: - 68% of the observations lie within one [[Standard Deviation|standard deviation]] of the [[Mean|mean]]; - 95% of the observations lie within two standard deviations of the mean; - 99.7% of the observations lie within three standard deviations of the mean. Compared to [[Chebyshev's Inequality|Chebyshev's theorem]], the empirical rule produces much stronger predictions.