What is "confirmation bias"

n. (context psychology English) A cognitive bias towards confirmation of the hypothesis under study.

Confirmation bias, also called confirmatory bias or myside bias, is the tendency to search for, interpret, favor, and recall information in a way that confirms one's preexisting beliefs or hypotheses, while giving disproportionately less consideration to alternative possibilities. It is a type of cognitive bias and a systematic error of inductive reasoning. People display this bias when they gather or remember information selectively, or when they interpret it in a biased way. The effect is stronger for emotionally charged issues and for deeply entrenched beliefs. People also tend to interpret ambiguous evidence as supporting their existing position. Biased search, interpretation and memory have been invoked to explain attitude polarization (when a disagreement becomes more extreme even though the different parties are exposed to the same evidence), belief perseverance (when beliefs persist after the evidence for them is shown to be false), the irrational primacy effect (a greater reliance on information encountered early in a series) and illusory correlation (when people falsely perceive an association between two events or situations).

A series of experiments in the 1960s suggested that people are biased toward confirming their existing beliefs. Later work re-interpreted these results as a tendency to test ideas in a one-sided way, focusing on one possibility and ignoring alternatives. In certain situations, this tendency can bias people's conclusions. Explanations for the observed biases include wishful thinking and the limited human capacity to process information. Another explanation is that people show confirmation bias because they are weighing up the costs of being wrong, rather than investigating in a neutral, scientific way.

Confirmation biases contribute to overconfidence in personal beliefs and can maintain or strengthen beliefs in the face of contrary evidence. Poor decisions due to these biases have been found in political and organizational contexts.Tuchman (1984) described a form of confirmation bias at work in the process of justifying policies to which a government has committed itself: "Once a policy has been adopted and implemented, all subsequent activity becomes an effort to justify it" (p. 245).

In the context of a discussion of the policy that drew the United States into war in Vietnam and kept the U.S. military engaged for 16 years despite countless evidences that it was a lost cause from the beginning, Tuchman argued:

Wooden-headedness, the source of self-deception is a factor that plays a remarkably large role in government. It consists in assessing a situation in terms of preconceived fixed notions while ignoring or rejecting any contrary signs. It is acting according to wish while not allowing oneself to be deflected by the facts. It is epitomized in a historian's statement about Philip II of Spain, the surpassing wooden head of all sovereigns: "no experience of the failure of his policy could shake his belief in essential excellence." (p.7)

Folly, she argued, is a form of self-deception characterized by "insistence on a rooted notion regardless of contrary evidence" (p.209)