A sample statistic that estimates a population parameter. The value of the estimator is referred to as a point estimate. There are several different types of estimators.

- If the expected value of the estimator equals the population parameter, the estimator is an unbiased estimator.
- If the expected value of the estimator does not equal the population parameter, it is a biased estimator.
- If the expected value of the estimator approaches the population value as the sample size increases, it is an asymptotically unbiased estimator.

Synonyms:

Biased estimator, Unbiased estimator