STANDARD DEVIATION ()

(Statistics) A measure of the variability of a series of data about its mean value. The standard deviation is equal to the square root of the Variance, from which it is derived, and measures the sum of the differences between a series' values and its mean. The standard deviation for a large data set (the population standard deviation) is calculated as: s (sigma) = (Sum(xi : x)2/n)-2 (sigma) = (Sum(xi : x)2/n)-2; where: xi is an individual observation; x is the mean of all observations; and n is the number of observations. xi is an individual observation; x is the mean of all observations; and n is the number of observations. For smaller data sets (typically less than 50) the sample standard deviation (s) is calculated by replacing n with n: 1 in this equation.