Conjunction fallacy

This bias arises because people often rely on heuristic thinking instead of probabilistic reasoning. When presented with a narrative that seems more representative of real-world knowledge, individuals tend to favor it, despite it being statistically less probable. This simplification caters to the human need to make quick judgements rather than complex analyses.

• A famous example introduced by Tversky and Kahneman involves a fictional woman named Linda. When participants are asked whether Linda, who is described as a philosophy major and socially active, is more likely to be a bank teller or a bank teller who is also a feminist, the majority incorrectly choose the latter despite it being a less likely conjunction of traits.
• In a medical context, a patient might believe they have a rare disease because their symptoms align with those described for that disease plus their unique traits, rather than the far more common condition with a few overlapping symptoms.

Some argue that the conjunction fallacy arises not solely from cognitive errors but also from misunderstandings in the framing of problems. They suggest that some instances attributed to the fallacy may involve different interpretations by respondents, where they focus on relevance or typicality instead of strict probability.