In probability and statistics, the standard deviation, generally denoted σ ('sigma'), is the most commonly used measure of statistical dispersion which is measured with the same units as the data. It is calculated as the square root of the variance and is therefore always a non-negative number.
The standard deviation of a sample, as opposed to a population, is denoted s.
See also: mean, skewness, kurtosis, raw score, standard score.
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