Confirmation bias

Confirmation bias is a type of statistical bias describing the tendency to search for or interpret information in a way that confirms one's preconceptions. In inductive inference, confirmation bias is a type of cognitive bias toward confirmation of the hypothesis under study. To compensate for this observed human tendency, the scientific method is constructed so that we must try to disprove our hypotheses. See falsifiability.

Confirmation bias is a phenomenon wherein decision makers have been shown to actively seek out and assign more weight to evidence that confirms their hypothesis, and ignore or underweigh evidence that could disconfirm their hypothesis. As such, it can be thought of as a form of selection bias in collecting evidence.

Among the first to investigate this phenomenon was Wason (1960), whose subjects were presented with three numbers (a triple):

and told that triple conforms to a particular rule. They were then asked to discover the rule by generating their own triples and use the feedback they received from the experimenter. Every time the subject generated a triple, the experimenter would indicate whether the triple conformed to the rule (right) or not (wrong). The subjects were told that once they were sure of the correctness of their hypothesized rule, they should announce the rule.

While the actual rule was simply “any ascending sequence,” the subjects seemed to have a great deal of difficulty in inducing it, often announcing rules that were far more complex than the correct rule. More interestingly, the subjects seemed to only test “positive” examples; that is, triples that subjects believed would conform to their rule and thus confirm their hypothesis. What the subjects did not do was attempt to falsify their hypotheses by testing triples that they believed would not conform to their rule. Wason referred to this phenomenon as the confirmation bias, whereby subjects systematically seek evidence to confirm rather than to deny their hypotheses.

The confirmation bias was Wason’s original explanation for the systematic errors made by subjects in the Wason selection task. In essence, the subjects were only choosing to examine cards that could confirm the given rule rather than disconfirm it.

Some have argued that confirmation bias may be the cause of self-perpetuating and self-fulfilling social beliefs.

This bias may occur at least partially because negatives are inherently more difficult to process mentally than positives.

More recent studies, however, have shown that while confirmation bias tends to be present as an initial condition, the repeated presentation of disconfirmatory data induces changes in theoretical thinking. In other words, the initial disconfirmatory data are regarded as the result of error, or some other externally attributed factor; it is only after similar results or data are repeatedly obtained that a change in causal reasoning strategies occurs.