68–95–99.7 rule

Rare card · No. 56356

In statistics, the 68–95–99.7 rule, also known as the empirical rule or 68–95–99.7 rule for a normal distribution and sometimes abbreviated 3sr or 3 σ, is a shorthand used to remember the percentage of values that lie within an interval estimate in a normal distribution: approximately 68%, 95%, and 99.7% of the values lie within one, two, and three standard deviations of the mean, respectively. In mathematical notation, these facts can be expressed as follows, where Pr() is the probability function, Χ is an observation from a normally distributed random variable, μ (mu) is the mean of the distribution, and σ (sigma) is its standard deviation: Pr ( μ − 1 σ ≤ X ≤ μ + 1 σ )...

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