Age-trend-related differences in tasks involving conjunctive probabilistic reasoning.

Conjunctive probabilistic reasoning has been studied at different ages to ascertain whether the conjunction fallacy is due to a task demand misinterpretation. Such a misinterpretation might occur because a task that requires a comparison between a superordinate class A and a subordinate class A&B is mistakenly interpreted as requiring a comparison between the two complementary subordinate classes of A (i.e., A&B and A&notB). Children (7- and 10-year-olds) and adults were required to make conjunctive probability judgments about problems for which explicit objective probabilities were provided. The total number of A items was kept constant and the frequencies of the A&B and of the A&notB items varied across problems. When the number of A&B items was smaller than the number of A&notB items, the frequency of congruent responses increased with age. When the number of A&B items was greater or equal to that of the A&notB items, the frequency of correct answers decreased.