Task

Participants are presented with a conditional statement of "if P then Q" type and instructed to indicate which of four cards (P, not-P, Q, and not-Q) they would turn in order to test this statement (participants report whether or not they would turn over each card). Note that the P card is both confirming and disconfirming while the Q card is only confirming.

Items (4)

Only nondeontic items are used.

Item 1

Each of the cards below has a number on one side and a letter on the other side. Which card(s) must be turned over to decide whether the following rule is true or false: If a card has a D on one side, then it has a 5 on the other side.

Cards: D, 7, 5, K
Confirming card: 5 (Q)
Disconfirming card: 7 (not-Q)

Screenshot (French version of the item):

Item 2

Each of the cards below has a number on one side and a color on the other side. Which card(s) must be turned over to decide whether the following rule is true or false: If a card has an even number on one side, then its opposite side is red.

Cards: 3, 8, red, orange
Confirming card: red (Q)
Disconfirming card: orange (not-Q)

Screenshot (French version of the item):

Item 3

Each of the envelopes below is sealed or not and bears a stamp. Which envelope(s) must be turned over to decide whether the following rule is true or false: If an envelope is sealed, then it has a 50-cent stamp on it.

Cards: sealed, unsealed, 50-cent stamp, 40-cent stamp
Confirming envelope: 50-cent stamp (Q)
Disconfirming envelope: 40-cent stamp (not-Q)

Screenshot (French version of the item):

Item 4

Each of the student copies below has a mark out of 20 on the front and a comment on the back. Which copy(s) must be turned over to decide whether the following rule is true or false: If a copy has a score greater than 16, then it has the comment "Excellent".

Copies: 18, Good, Excellent, 15
Confirming copy: Excellent (Q)
Disconfirming copy: Good (not-Q)

Screenshot (French version of the item):

Scoring

In each item, the confirmation bias score is the difference between the response (Yes = 1 vs. No = 0) to the confirming card (Q) and the response to the disconfirming card (not-Q). The total score is calculated as the average of the four scores.