A cognitive bias is a pattern of deviation in judgment that occurs in particular situations. Implicit in the concept of a “pattern of deviation” is a standard of comparison; this may be the judgment of people outside those particular situations, or may be a set of independently verifiable facts. The existence of some of these cognitive biases has been verified empirically in the field of psychology.

Cognitive biases are instances of evolved mental behavior. Some are presumably adaptive, for example, because they lead to more effective actions in given contexts or enable faster decisions when faster decisions are of greater value. Others presumably result from a lack of appropriate mental mechanisms, or from the misapplication of a mechanism that is adaptive under different circumstances.

Cognitive bias is a general term that is used to describe many distortions in the human mind that are difficult to eliminate and that lead to perceptual distortion, inaccurate judgment, or illogical interpretation.[1]