Variance

The variance of a random variable $X$ is: $Var(X)=E(X-E(X){)}^2$

It measures how spread out the values of a random variable are from its expected value (mean).

Context

Variance is one of the most important measures in statistics. For example, two datasets can have the same mean but very different variances: $\{4,5,6\}$ has low variance while $\{0,5,10\}$ has high variance. The square root of variance is the standard deviation.

See Also

• event
• sample space
• conditional probability