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Standard Deviation

Rule

Standard Deviation

Standard deviation is a commonly used measure of spread. It is a measure of how much a randomly selected value from a data set is expected to differ from the mean. To denote the standard deviation, the Greek letter σ\sigma is used, which is read as "sigma." To calculate a standard deviation, the rule σ=(x1xˉ)2+(x2xˉ)2++(xnxˉ)2n \sigma = \sqrt{ \dfrac{ (x_1 - \bar{x})^2 + (x_2 - \bar{x})^2 + \ldots + (x_n - \bar{x})^2}{n} } is used, where nn is the number of values in the data set and xˉ\bar{x} is the mean of the set.