確証バイアス

Confirmation bias is the tendency to seek out or interpret information in a way that confirms an existing belief. When investigating a topic, people selectively attend to evidence supporting their preconceptions while ignoring contradictory data. This selective search falsely validates prevailing beliefs without awareness, preventing objective evaluation of alternative hypotheses.

When people are motivated to defend a preferred idea, they deliberately discount or ignore contradictory information, interpret stories to reinforce personal opinions, and ask questions prompting specific answers. This motivated reasoning strengthens confirmation bias, as emotional investment makes people resistant to evidence challenging their preconceptions.

An employer expecting a job applicant to be incompetent treats them negatively, causing the applicant to disengage. The employer then interprets the applicant's withdrawn behavior as evidence of incompetence, reinforcing the initial stereotype. The employer overlooks early competent responses, focusing only on later disengaged behavior that resulted from their own biased treatment.

Confirmation bias reinforces stereotypes by causing people to notice behavior confirming their expectations while ignoring contradictory evidence. For example, if you believe your professor is unkind, you notice rude instances but overlook pleasant interactions. This selective attention strengthens stereotypic beliefs and can lead to prejudice and discrimination in social interactions.

Both confirmation bias and the representativeness heuristic decision making involve using limited information to make judgments. Confirmation bias causes selective attention to supporting evidence, while the representativeness heuristic relies on how closely something matches a mental prototype. Together, they can lead to flawed conclusions when people ignore base rates and contradictory data.

To thoroughly test viewpoints, people should explore both sides—evidence for and against their perspectives—before establishing conclusions. This balanced approach requires actively seeking contradictory information rather than selectively attending to supporting evidence. Conscious effort to consider alternative hypotheses helps reduce the automatic tendency to confirm existing beliefs.

Confirmation bias operates largely outside conscious awareness. People believe they are objectively investigating topics while unconsciously filtering information. This automatic process happens without intention or awareness of being misleading, making it difficult to recognize in oneself and requiring deliberate strategies to counteract its effects on judgment and decision-making.