The conjunction fallacy is a reasoning error in which people judge the probability of two events occurring together, a conjunction, to be greater than the probability of one of those events occurring alone, even though this is logically impossible under the rules of probability. It was demonstrated most famously by the psychologists Amos Tversky and Daniel Kahneman in their 1983 "Linda problem," in which participants given a detailed description of a fictional woman ranked the statement that she was "a bank teller and active in the feminist movement" as more probable than the plain statement that she was "a bank teller," even though the former is a strict subset of the latter. Tversky and Kahneman attributed the fallacy to the representativeness heuristic, in which a scenario that matches a stereotype or is internally coherent feels more probable regardless of its actual logical or statistical structure.
Facts
Core ClaimIn the original Linda problem experiment, the majority of participants judged the conjunction, that Linda is a bank teller and active in the feminist movement, as more probable than the plain statement that she is a bank teller, even though a conjunction can never be more probable than either of its parts alone. 1 First Described Year Connections
Associated With
Demonstrated with Kahneman in the 'Linda problem' as part of their heuristics-and-biases research.
Demonstrated with Tversky in the 'Linda problem' as part of their heuristics-and-biases research.
In Branch
Sources
1. Wikipedia: Conjunction fallacy
Wikimedia FoundationLinda problem subsection, majority result
The majority of those asked chose option 2. However, this is logically impossible: if Linda is a bank teller active in the feminist movement, then she is a bank teller.
Tversky and Kahneman (1983) subsection
Tversky and Kahneman followed up their original findings with a 1983 paper that looked at dozens of new problems, most of these with multiple variations.
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