Standard Deviation

The standard deviation (this term was first used by Pearson, 1894) is a commonly used measure of variation. The standard deviation of a population of values is computed as:

s = [S(xi-m)2/N]1/2

where

m 

is the population mean

N  

is the population size

The sample estimate of the population standard deviation is computed as:

s = [S(xi-x-bar)2/(n-1)]1/2

where

x-bar  

is the sample mean

n  

is the sample size

See also, Descriptive Statistics Overview.