Confirmation bias is the tendency to seek, interpret, favor, and recall information in a way that confirms one's prior beliefs or hypotheses. It is perhaps the most pervasive and consequential cognitive bias, operating across domains from scientific reasoning to political judgment to everyday belief maintenance. Confirmation bias does not necessarily reflect motivated reasoning — it can result from cognitive processes that favor positive testing and similarity-based retrieval.
Forms of Confirmation Bias
Confirmation bias operates at multiple stages of information processing. In information search, people preferentially seek evidence that could confirm their hypothesis (positive test strategy) rather than evidence that could disconfirm it. In interpretation, ambiguous evidence is construed as consistent with existing beliefs. In memory, belief-consistent information is better remembered than belief-inconsistent information. These biases at each stage compound to create a powerful self-reinforcing cycle.
Wason's 2-4-6 Task
Wason (1960) demonstrated confirmation bias using a number-sequence task. Participants were told that 2-4-6 follows a rule and asked to discover it by generating test sequences and receiving feedback. Most participants hypothesized specific rules (e.g., "increasing by 2") and tested only confirming instances (4-6-8, 10-12-14). Few tested disconfirming instances (1-3-5 or 1-2-3) that would have revealed the actual rule was simply "any ascending sequence." The positive test strategy — testing instances consistent with one's hypothesis — is a fundamental driver of confirmation bias.
When beliefs are emotionally invested (political opinions, self-concept, group identity), confirmation bias intensifies through motivated reasoning. People actively argue against threatening information, apply higher evidential standards to belief-inconsistent evidence, and selectively expose themselves to congenial information sources. Political polarization, persistence of conspiracy theories, and resistance to attitude change all reflect the combined effects of cognitive confirmation bias and motivational processes that protect valued beliefs.