Confirmation bias is the tendency to search for, interpret, favor, and remember evidence that supports existing beliefs. Someone affected by it may welcome information that agrees with a prior view while dismissing, overlooking, or reinterpreting evidence that conflicts with it.
The bias can appear in everyday decisions, political arguments, financial judgments, medical reasoning, and scientific work. For example, a person convinced that a treatment works may notice every improvement after using it but discount cases in which it fails. Searching only for confirming examples can make a weak belief feel strongly supported.
English psychologist Peter Wason helped establish the term through studies of hypothesis testing in the 1960s. Later researchers argued that some of his findings may reflect a broader “positive test strategy”: people often test a working idea in the easiest way rather than actively seeking disconfirming evidence.
Confirmation bias is not the same as a self-fulfilling prophecy. In a self-fulfilling prophecy, expectations help cause the predicted result; confirmation bias concerns how people gather, interpret, or remember information. Deliberately looking for strong counterexamples is one way to reduce its influence.