Confirming the Confirmation Bias

Suppose someone deals out four cards, each with a letter on one side and a number on the other. Only one side of each card is showing, as depicted here. Your task is to find out whether the following rule is true: “If a card has a vowel on one side, then it has an even number on the other side.” Which two cards do you need to turn over to find out? The majority of people say they would turn over the E and the 6, but they are wrong. You do need to turn over the E (a vowel), because if the number on the other side is even, it confirms the rule, and if it is odd, the rule is false. However, the card with the 6 tells you nothing. The rule does not say that a card with an even number must always have a vowel on the other side. Therefore, it doesn’t matter whether the 6 has a vowel or a consonant on the other side. The card you do need to turn over is the 7, because if it has a vowel on the other side, that would disconfirm the rule. People do poorly on this problem because they are biased to look for confirming evidence and to ignore the possibility of disconfirming evidence