Variance

The variance is a widely used measure of variability. It is defined as the mean squared deviation of scores from the mean. The formula for variance computed in an entire population is

where σ^{2}
represents the variance, μ is the mean,
and N is the number of scores.

When computed in a sample in order to estimate the variance in the population, the population is

where s^{2} is the estimate of variance,
M is the sample mean, and N is the number of scores in the sample.

See also standard deviation.