Scientific Volume Imaging

Standard deviation

The standard deviation σ of a series of values x_i is calculated as

$$\sigma\ =\ \sqr{\frac{1}{N} \sum (x_i - x_{avg})^2}$$

with x_avg the average of all the x_i, and N the total number of values.

Its squared value σ² is an estimator of the variance.

See http://en.wikipedia.org/wiki/Standard_deviation and http://en.wikipedia.org/wiki/Variance