The Conjunction Fallacy: Differential Incidence as a Function of Descriptive Frames and Educational Context
Abstract The frequency of the conjunction fallacy, in which individuals report that the conjunction of two events is more rather than less likely than one of the events alone, was assessed in college students when questions were asked with and without a “framing description,” when nothing was known about the person being judged, in questions presented in a more qualitative format, and between groups studying different subjects. The frequency of the fallacy varied sharply across student groups and groups differed in their susceptibility to contextual effects. Importantly, the conjunction fallacy occurred for about one-quarter of subjects even when the framing description was eliminated and the question worded to facilitate a logical approach. Experiment 2 found that subjects’ descriptions of their problem-solving strategies appeared largely unrelated to their performance. In Experiment 3, logic students performed the task near the end of their course; a substantial number, 43%, committed the fallacy. In Experiment 4, 41% of students committed the fallacy even without the framing description.