The bias of an estimator θ^~ is defined as B(θ^~) congruent 〈θ^~ 〉 - θ. It is therefore true that θ^~ - θ | = | (θ^~ - 〈θ^~ 〉) + (〈θ^~ 〉 - θ) | = | (θ^~ - 〈θ^~ 〉) + B(θ^~). An estimator for which B = 0 is said to be unbiased estimator.

biased estimator | estimator | unbiased estimator