Variance

The square of the difference from the mean for each data value, summed and divided by one less than the number of values. An expression of the so-called "second moment" which describes the variability around the mean. The square root of the variance is the standard deviation.

for the data series: x₁, x₂, x₃,....,x_N the variance is:

See also: Mean, Standard Deviation, Standard Error, Statistic.