When a person reaches a conclusion (by making a decision or accepting a belief as true), he or she will actively seek information that confirms this idea, while disregarding evidence that does not support it. This psychological theory is called confirmation bias, or positive test strategy, and is a common, unconscious behavior. The term "confirmation bias" was first coined by Peter Wason in 1960, although the idea was noted earlier by Francis Bacon who said, "It is the peculiar and perpetual error of the human understanding to be more moved and excited by affirmatives than by negatives." Thus, a person will readily accept evidence that supports an idea, while subjecting conflicting data to critical evaluation.
In a study by Lord, Ross, and Lepper, 24 proponents and 24 opponents of the death penalty read studies that were for or against it. None of the subjects changed their initial opinions, no matter which studies they read. In fact, the subjects tended to become more polarized in their views, either incorporating the new information into their initial view or trying to discredit the studies by finding flaws.
Furthermore, this theory appears in every day situations, and demonstrates that personal biases can affect results. For instance, individuals who believe in psychic readings will attempt to match their lives to their readings. Later, they tend to remember the parts of the reading that fit, while forgetting the parts that did not. People use selective memory and selective thinking to confirm their beliefs, which diminishes their objectivity.
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