Confirmation Bias
We search for, interpret, and remember information in ways that confirm what we already believe.
Origin & History
Confirmation Bias was formally described by psychologist Peter Wason in his 1960 card-selection experiment. Participants were given a rule to test and consistently selected only cards that could confirm the rule — ignoring cards that could have disproven it. Wason called this 'verification bias.' The term 'confirmation bias' was popularized by cognitive psychologist Raymond Nickerson in a 1998 review article that documented its pervasiveness across decision-making contexts.
Real-World Examples
A manager who believes an employee underperforms documents every mistake and discounts every success as luck. Colleagues who hold no prior belief rate the same employee as a top performer. The manager's file shows only negatives.
Once a physician anchors on an initial diagnosis, subsequent symptoms are interpreted as consistent with it — even when they contradict it. Diagnostic errors often trace back to confirmation bias operating on the first assessment.
Investors who have decided to buy a stock selectively read positive research and dismiss negative analysis as biased or incomplete. The decision was made; the research became post-hoc justification.
Why It Matters
Confirmation Bias is arguably the most pervasive cognitive bias because it distorts information at every stage: what we seek, how we interpret what we find, and what we remember afterward. The result is that experience and evidence strengthen rather than challenge prior beliefs. The most effective countermeasure is the practice of steelmanning — deliberately constructing the strongest version of the opposing view — before reaching any conclusion. If you can't articulate why you might be wrong, you probably haven't looked hard enough.
Related Laws
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The tendency to search for, interpret, and remember information in ways that confirm our existing beliefs — while discounting or ignoring contradicting evidence.
By actively seeking disconfirming evidence: deliberately looking for information that could prove you wrong, and treating the quality of that search as a measure of the quality of your conclusion.
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