Editing Estimator (section)

===Variance===
The [[variance]] of <math>\widehat{\theta}</math> is the expected value of the squared sampling deviations; that is, <math>\operatorname{Var}(\widehat{\theta}) = \operatorname{E}[(\widehat{\theta} - \operatorname{E}[\widehat{\theta}]) ^2]</math>. It is used to indicate how far, on average, the collection of estimates are from the ''expected value'' of the estimates. (Note the difference between MSE and variance.) If the parameter is the bull's-eye of a target, and the arrows are estimates, then a relatively high variance means the arrows are dispersed, and a relatively low variance means the arrows are clustered. Even if the variance is low, the cluster of arrows may still be far off-target, and even if the variance is high, the diffuse collection of arrows may still be unbiased. Finally, even if all arrows grossly miss the target, if they nevertheless all hit the same point, the variance is zero.