In research, the amount by which the true value of a metric differs from the value that would be obtained if a given research design were executed repeatedly, as opposed to a difference due to sampling variability. This occurs, for example, when those being measured do not accurately represent the target population. Also occurs when there is a predisposition or prejudice in favor of or against a thing, idea, concept, person or group in comparison with another, in a way that produces either an unfavorable or distorted perspective or interpretation. (See “Bias, Cognitive”; “Bias, Selection”; “Bias, Response).”