Confirmation bias is the tendency to notice, seek out and believe information that fits what you already think — while giving far less weight to whatever would prove you wrong.
Peter Wason ran the founding 1960 experiment. The phrase became standard later, through 1970s work and Nickerson's 1998 review article. Whether Wason himself coined it in his later writing or others fixed the name is disputed.
// Where it sits
It starts in which question you ask - and carries on through how you read the answer.
What it really means
Peter Wason's 1960 experiment is one of the cleanest demonstrations of a bias ever built, and its cleverness is that it strips out everything people usually blame. No politics. No ego. No money. Just three numbers on a card — 2, 4, 6 — and an instruction: work out the rule by proposing triples of your own, and I'll tell you yes or no.
Almost everyone forms the same hypothesis immediately: even numbers ascending by two. And then almost everyone tests it the same way. 8-10-12. Yes. 20-22-24. Yes. 100-102-104. Yes. Three confirmations, growing confidence, wrong answer. The actual rule was any three ascending numbers, and the single test that would have exposed it — trying something the hypothesis forbids, like 1-2-3 — is the one hardly anyone runs.
That's what makes confirmation bias worse than the usual telling of it. It isn't wilfully ignoring inconvenient facts; that would be easier to catch. It's that the mind, asked to test an idea, reliably generates the experiments the idea will pass. Every result comes back positive, which feels exactly like being right. And expertise doesn't rescue you — it mostly enlarges the pool of evidence you can select from.
Where it comes from
The Latin is literal about it: confirmare is 'to make firm, strengthen'. English narrowed the noun long before the psychology arrived — by the late 14th century confirmation meant verification and supporting evidence, which is the sense Wason's term uses.
Myths & misconceptions
Confirmation bias means deliberately ignoring evidence you don't like.
It's mostly unconscious. Wason's participants weren't cheating — they generated tests their hypothesis would pass, a habit researchers call a positive test strategy. You can be sincerely trying to be fair and still do it.
Intelligent, well-educated people are largely immune.
Wason's subjects were intelligent young adults and most still failed. Later research finds it in analysts, clinicians and scientists — expertise gives you more evidence to use selectively, not less bias.
Compare & contrast
Confirmation bias vs motivated reasoning
Confirmation bias is about which evidence you look at; motivated reasoning is about wanting a particular answer. The distinction matters because you can show confirmation bias with nothing at stake at all — Wason's number triples had no emotional content whatsoever.
| // | Confirmation bias | Motivated reasoning |
|---|---|---|
| Driven by | Test strategy | Desired conclusion |
| Needs a stake | No | Yes |
| Conscious | Rarely | Sometimes |
| Fix | Test the opposite | Name the want |
How it connects
- Cognitive Dissonanceone cheap way to end dissonance is to stop encountering the evidence that caused it.
- Barnum EffectBarnum supplies a vague statement; confirmation bias goes hunting for the memories that fit it.
Tell it apart
Questions people ask
- What is confirmation bias in simple terms?
- It's the habit of collecting evidence that agrees with you. Decide a new colleague is disorganised and you'll register every missed deadline while quietly discounting the three reports they filed early — and finish the month more certain than you started.
- What was the 2-4-6 experiment?
- Wason showed people 2, 4, 6 and asked them to work out the rule by testing triples. Almost everyone tested 8-10-12, 20-22-24 — sequences fitting their guess of 'even numbers going up in twos'. The real rule was 'any three ascending numbers'. Trying 1-2-3 would have cracked it instantly. Hardly anyone tried.
- How do you counter it?
- Test what would prove you wrong rather than what would prove you right. Before buying the car you've fallen for, don't search its name plus 'review' — search its name plus 'problems', and set the question as 'what would make me walk away?'