Confirmation Bias
Edited by Paweł Raja, PhD · Published
Definition
Confirmation Bias is the tendency to search for, interpret and remember information in ways that confirm what you already believe, while giving less weight to evidence against it.
- Also known as:
- Confirmatory bias, Myside bias
- Category:
- Judgment & Belief
- Impact:
- High
- Landmark study:
- Wason (1960)
- Evidence here:
- 8 cited studies
Why it happens: the psychology of confirmation bias
Confirmation bias is not a single error but a family of them (Nickerson, 1998). People seek information that fits a belief they already hold, interpret ambiguous evidence in its favor, and remember supporting facts better than contradicting ones.
Peter Wason's (1960) 2-4-6 task showed the search side. Asked to discover a rule that the sequence 2-4-6 obeys, most participants tested only sequences that fitted their own hypothesis (such as 8-10-12) and rarely tried sequences that could prove it wrong — so they confidently announced rules that were too narrow.
Lord, Ross and Lepper (1979) showed the interpretation side. Supporters and opponents of capital punishment read the same pair of studies and each judged the study agreeing with them to be better designed. Exposure to mixed evidence made both groups more extreme.
Motivation plays a role: people reason more critically about conclusions they dislike (Kunda, 1990). But the bias also arises without motivation, simply because testing a hypothesis by looking for confirming cases is cognitively easier. A meta-analysis by Hart and colleagues (2009) found a consistent, moderate preference for information that agrees with one's views.
Confirmation Bias examples
In a classic Stanford study, supporters and opponents of the death penalty read the same mixed evidence; each side rated the studies supporting its view as more convincing and came away more polarized than before.
- Money: an investor who likes a company reads its good news closely and skims past warning signs in the same report.
- Health: a doctor who settles on a diagnosis early may order tests that can confirm it rather than tests that could rule it out.
- Health: someone convinced a supplement works remembers the good days after taking it and forgets the bad ones.
- Work: in Snyder and Swann's (1978) experiments, people asked to find out whether someone was an extravert chose questions about parties and socializing, while people testing for introversion asked about quiet activities — each set of questions invited confirming answers.
- Science and reasoning: in Wason's (1960) 2-4-6 task, most people tested only number sequences that fitted their own guess about the rule, so they never discovered it was simply 'any ascending numbers'.
- Law: an investigator who decides early on a suspect can read every new piece of ambiguous evidence as pointing to that person.
- Everyday life: people choose news sources and social feeds that agree with them, then treat the agreement as evidence they are right.
How to avoid confirmation bias
- Ask what would change your mind, and look for exactly that evidence. Testing a belief means trying to falsify it, not collecting more support.
- Consider the opposite. Listing reasons your view could be wrong is one of the few debiasing techniques with consistent experimental support.
- Steel-man the other side: state the strongest version of the opposing argument before rejecting it.
- Separate searching from judging. Decide what evidence you will look at, and how you will weigh it, before you know what it says.
How to design for it (nudge strategy)
Build disconfirmation into the process: require a 'case against' section in proposals, assign a rotating devil's advocate, and present the strongest opposing evidence alongside the recommended option.
Ethical use: design for choices people would endorse on reflection — a nudge, not sludge. Be transparent and keep opting out easy.
Key studies
In the 2-4-6 task, most people tested only confirming cases and so failed to discover the true rule.
Wason, P. C. (1960). On the failure to eliminate hypotheses in a conceptual task. Quarterly Journal of Experimental Psychology, 12(3), 129–140. DOI →
People testing whether someone was an extravert (or an introvert) preferentially chose interview questions that would confirm that hypothesis.
Snyder, M., & Swann, W. B., Jr. (1978). Hypothesis-testing processes in social interaction. Journal of Personality and Social Psychology, 36(11), 1202–1212. DOI →
People on both sides of the death-penalty debate rated agreeing evidence as stronger, and mixed evidence polarized them further.
Lord, C. G., Ross, L., & Lepper, M. R. (1979). Biased assimilation and attitude polarization: The effects of prior theories on subsequently considered evidence. Journal of Personality and Social Psychology, 37(11), 2098–2109. DOI →
Reviewed evidence that the desire to reach a particular conclusion shapes how people search for and evaluate information.
Kunda, Z. (1990). The case for motivated reasoning. Psychological Bulletin, 108(3), 480–498. DOI →
The standard review of confirmation bias across science, medicine, law and everyday reasoning.
Nickerson, R. S. (1998). Confirmation bias: A ubiquitous phenomenon in many guises. Review of General Psychology, 2(2), 175–220. DOI →
Across many studies, people showed a moderate preference for information that supports their existing views.
Hart, W., Albarracín, D., Eagly, A. H., Brechan, I., Lindberg, M. J., & Merrill, L. (2009). Feeling validated versus being correct: A meta-analysis of selective exposure to information. Psychological Bulletin, 135(4), 555–588. DOI →
Key research
- Errors in Probabilistic Reasoning and Judgment BiasesDaniel J. Benjamin · Handbook of Behavioral Economics: Applications and Foundations 1 (2019)
- Managing Self-Confidence: Theory and Experimental EvidenceMarkus M. Möbius, Muriel Niederle, Paul Niehaus, Tanya S. Rosenblat · Management Science (2022)
Related biases
Confirmation Bias: frequently asked questions
What is confirmation bias in simple terms?
Confirmation bias is seeing what you expect to see: favoring information that supports what you already believe and discounting information that challenges it.
What are some examples of confirmation bias?
Reading only reviews that praise a product you have already decided to buy; a detective focusing on evidence against the first suspect; people on opposite sides of a debate both finding the same mixed evidence convincing.
Who discovered confirmation bias?
The English psychologist Peter Wason coined the term in the 1960s after his 2-4-6 and selection-task experiments, although the tendency had been described much earlier, including by Francis Bacon in 1620.
What is the difference between confirmation bias and motivated reasoning?
Motivated reasoning is driven by wanting a particular conclusion to be true. Confirmation bias can happen without any such desire, simply because looking for confirming cases is the easiest way to test an idea.
How do you avoid confirmation bias?
Actively look for evidence that would disprove your view, write down the best counter-argument, invite people who disagree, and set your evaluation criteria before you see the data.
Cite this page
Raja, P. (Ed.). (2026, 8 Oct 2026). Confirmation Bias. Behavioral Economics Lab. https://www.behavioraleconomicslab.com/biases/confirmation-bias