standard deviation

The standard deviation (σ) is a measure of spread in \term{statistics}. It is caclualted by taking the square root of the \term{variance}, which is itself the average of the square of difference of values from their \term{arithmetic mean}. The standard deviation of a simple set of N numbers x_i> with mean μ is:
      σ   =   √ ( Σ (x_i>− μ)²  /  N )