Probability And Statistics

This article/section deals with mathematical concepts appropriate for late high school or early college.

Variance is a measure in statistics of the dispersion of a set of values (represented as ). It is defined as

where the expected value of X is E(X).

The formula for variance must not be confused with the formula

which is the formula for a point estimate of the true variance from a sample of size n. As such this estimator itself has a variance which, as the formula indicates, decreases as the sample size increases.