How can bias influence scientific conclusion?

A cognitive bias is a pattern of poor judgment, often triggered by a particular situation. Identifying "poor judgment," or more precisely, a "deviation in judgment," requires a standard for comparison, i.e. "good judgment". In scientific investigations of cognitive bias, the source of "good judgment" is that of people outside the situation hypothesized to cause the poor judgment, or, if possible, a set of independently verifiable facts. The existence of most of the particular cognitive biases listed below has been verified empirically in psychology experiments.

Cognitive biases, like many behaviors, are influenced by evolution and natural selection pressure. Some are presumably adaptive and beneficial, for example, because they lead to more effective actions in given contexts or enable faster decisions, when faster decisions are of greater value for reproductive success and survival. Others presumably result from a lack of appropriate mental mechanisms, i.e. a general fault in human brain structure, or from the misapplication of a mechanism that is adaptive (beneficial) 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.