HOW ALIKE IS IT VERSUS HOW LIKELY IS IT - A DISJUNCTION FALLACY IN PROBABILITY JUDGMENTS

One event cannot be more probable than another that includes it. Judgi ng P(A & B) to be higher than P(A) has been called the conjunction fal lacy. This study examined a disjunction fallacy. Ss received brief cas e descriptions and ordered 7 categories according to 1 of 4 criteria: (a) probability of membership, (b) willingness to bet on membership, ( c) inclination to predict membership, and (d) suitability for membersh ip. The list included nested pairs of categories (e.g., Brazil-South A merica). Ranking a category more probable than its superordinate, or b etting on it rather than its superordinate, is fallacious. Prediction, however, may be guided by maximizing informativeness, and suitability need conform to no formal rule. Hence, for these 2 criteria, such a r anking pattern is not fallacious. Yet ranking of categories higher tha n their superordinates was equally common on all 4 criteria. The resul ts support representativeness against alternative interpretations.