In a variation on the “Wason selection task”, students in a research study were asked to test the rule “if a card has D on one side, it has a 3 on the other”. They were then shown four cards, which had either a letter (D or F) or a number (3 or 7) on them, and were asked which cards they would turn over to validate the rule.  The correct answer was the D and 7 cards. If a D card had anything other than a 3 on the other side, the rule was disconfirmed; ditto if a 7 had a D on the other side.

Most students got it wrong – they said they would look at the F and 3 cards*.  Their error was in seeking to confirm the rule, rather than disconfirm it. But a rule is only a rule if it applies across the board; therefore, all you have to do is find one instance where it doesn’t apply and the rule is invalidated.

The hopeful thing about this study is that if students were asked what cards they had to turn over to falsify the rule, they usually got it right. Moral of the story: it’s not all that hard to overcome our biases. There’s hope for humanity yet.

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* Neither the F nor 3 card had any bearing on the question because nothing on the other side could disconfirm the rule.

Reference:

Feist, Gregory J. (2006) The Psychology of Science and the Origins of the Scientific Mind. New Haven: The University Press