Confirmation bias is the tendency of people’s minds to seek out information that supports the views they already hold. It also leads people to interpret evidence in ways that support their pre-existing beliefs, expectations, or hypotheses.
People easily accept new information that is consistent with their beliefs, but are skeptical of information that contradicts their beliefs. In one study, teachers were told that certain students were especially promising… even though the students were really chosen at random. Based on this false belief, teachers gave more praise and attention to the chosen students… who improved more because of the teachers’ expectations. In other words, the confirmation bias can create self-fulfilling prophecies.
For example, when physicians have an idea about a patient’s diagnosis, they may focus on evidence that supports their theory while they undervalue evidence that supports an equally plausible alternative diagnosis.
Likewise, police officers who accept stereotypes that link young black men to crime may gather and process clues in a one-sided way when investigating a crime with a black suspect. As Nobel-prize winner Daniel Kahneman warns, even scientists who commit to a theory tend to disregard inconsistent facts, concluding that the facts are wrong, not the theory.
So the confirmation bias can easily lead us to reach inaccurate –and even unethical– conclusions. It’s essential to recognize our vulnerability to confirmation bias, and actively guard against it by being open to evidence that is not consistent with our beliefs and theories.