Definition: In statistics and probability theory, a biased estimator is an estimator that has some bias. In other words, it can be expected to produce estimates with values closer or farther from the population parameters than if the estimator were unbiased. Bias refers to how well an estimate performs under different conditions of data. For example, in a situation where all observations are perfectly equal in size (i.e., no measurement error), the bias is zero. However, when there's some degree of variability among observations, the bias