Confirmation bias
The tendency to look for, favour and remember evidence that fits what we already believe, and to overlook evidence that does not.
Confirmation bias is the habit of noticing, seeking and remembering the evidence that supports what we already think, while giving less weight to evidence against it. It is usually automatic, not deliberate dishonesty.
An everyday example: after reading that a horoscope 'fits', we remember the lines that matched and forget the ones that did not.
In a famous 1960 experiment, the psychologist Peter Wason told people that the numbers 2, 4, 6 followed a hidden rule and asked them to find it by testing their own sets of three numbers. The rule was simply 'any three numbers in increasing order', yet many people announced far more specific rules, because they mostly tested examples that fitted their own guess, such as 11, 13, 15, rather than ones that could prove it wrong.
A common misconception is that testing examples that fit your idea is always a mistake. It is not: such tests can be informative. The trap is never trying the test that could show you are wrong.
See it in action
Coming up in future stories
- The Dead Man Who Fooled Hitler 30 April 1943 · off Huelva, Spain