The variance formula is S2 =1/n [(x1-x) 2+(x2-x) 2+...+(xn-x) 2], and the standard deviation formula is sample standard deviation = square root of arithmetic variance = s = sqrt ((x668)). Variance is a measure of dispersion when probability theory and statistical variance measure random variables or a set of data. The standard deviation, also called mean square deviation in Chinese environment, is the square root of the arithmetic mean value deviating from the mean square, and is expressed by σ. The standard deviation is the arithmetic square root of variance.