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Biased Estimator

An biased estimator is one which delivers an estimate which is consistently different from the parameter to be estimated. In a more formal definition we can define that the expectation E of a biased estimator is not equal to the parameter. In principle we can differentiate between two types of bias:

Note that an unbiased statistic is not necessarily an accurate statistic. If the variance of a statistic is high it can still be unbiased.

Last Update: 2006-Jšn-17