VARIANCE

(Statistics) A measure of the spread or dispersion of a variable about its Mean or Arithmetic Mean value. The variance is calculated by taking the sum of the squares of the deviations, that is, the sum of the difference between the observed value and the series mean value, and dividing by the sample size (number of observations). The variance for a large data set (the population variance) is calculated as: s2 (sigma) = (xi : x)2/n (sigma) = (xi : x)2/n; 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 variance (s2) is calculated by replacing n with n: 1 in this equation. The positive square root of the variance is called the Standard Deviation. Both the variance and the standard deviation are non-negative, by definition.