Psychology › Thinking, memory & biases › Heuristics and biases
Confirmation bias
1960 (Wason)· Finding or experiment
Well replicatedStrong, repeated evidence.
Confirmation bias is the tendency to seek, notice and remember evidence that supports what we already believe.
See it on the Psychology map →What it says
In 1960 Peter Wason gave people the number series 2-4-6 and asked them to find the rule behind it. Most tested only examples that fit their guess, such as 8-10-12, and grew confident in wrong rules; the true rule was simply 'any ascending numbers'. Later studies found people rate supporting evidence as stronger, prefer news that agrees with them, and remember hits better than misses. Science uses control groups and blind testing partly to counter it.
Why it matters
It keeps bad decisions alive: buyers and investors collect reasons a deal is good. Deliberately building the case against, as in serious due diligence, is the main remedy.
Think of it like
Like ordering a building inspection and reading only the pages that say the roof is fine.
The evidence
Well replicated across many tasks and fields, from Wason's puzzles to studies of doctors, detectives and investors; reviewed by Raymond Nickerson in 1998.
Open questions
Researchers debate whether it is purely a flaw: testing ideas you expect to hold is often efficient, and arguing in groups can cancel individual bias out.
Connections (2)
▸Confirmation bias is usually filed under Heuristics and biasesWell replicated
The connection
Confirmation bias came from Peter Wason's reasoning research, not from Kahneman and Tversky, but it fits the same pattern: a reasonable mental strategy, testing what you expect, that produces systematic errors. Textbooks and reviews of judgment now treat it as one of the core biases.
Who showed it and when
Wason at University College London, 1960 (the 2-4-6 task) and 1966 (the card selection task); reviewed by Raymond Nickerson in 1998.
The evidence
It appears in standard catalogs of judgment biases and in decision research alongside anchoring and availability.
Open questions
It is not tied to one heuristic; researchers debate whether it is a single bias or a family of habits in search, interpretation and memory.
▸Cognitive dissonance (Festinger) is one proposed driver of Confirmation biasMixed evidence
The connection
Festinger predicted people protect their decisions by seeking supportive information and avoiding the rest. A 1957 study found new car owners read more ads for the model they had just bought. That selective exposure is one source of confirmation bias, though the bias also arises from plain reasoning shortcuts.
Who showed it and when
Festinger's 1957 theory and Danuta Ehrlich and colleagues' 1957 car-buyer study; a 2009 meta-analysis by William Hart and colleagues pooled about 90 studies.
How solid is it?
The 2009 meta-analysis found people were about twice as likely to pick information agreeing with their views, especially when strongly committed.
Open questions
How much confirmation bias is emotionally motivated, as dissonance theory says, versus a cold reasoning habit, as Peter Wason's 1960 rule-discovery task suggested.