The variance is a widely used measure of variability. It is defined as the mean squared deviation of scores from the mean. The forumla for variance computed in an entire populaton is
where σ2 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 forumula is
where s2 is the estimate of variance M is the sample mean, and N is the number of scores in the sample.
See also standard deviation.