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. Judging P(A &amp; B) to be higher<br>than P(A) has been caIled the conjunction fallacy- This study examined a disjullctioll fallaQ&lt; Ss<br>received brief case descriptions and ordered 7 categories according to 1 of 4 criteria: (a) probability<br>of membership, (b) wiIlingness to bet on membership, (c) inclination to predict membership, and (d)<br>suitability for membership. The list included nested pairs of categories (e.g., Brazil-South America).<br>Ranking a category more probable than its superordinate, or betting on it rather than its superordinate,<br>is fallacious. Prediction, however, may be guided by maximizing informativeness, and suitability<br>need conform to no formal rule. Hence, for these 2 criteria, such a ranking pattern is not<br>fallacious. Yet ranking of categories higher than their superordinates was equally common on all 4<br>criteria. The results support representativeness against alternative interpretations.