Conjunction fallacy

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Fundamental laws of probability state that a subset cannot be more likely than a larger set that includes the subset. In other words – conjunction canon be more probable than any of its description. However, using representativeness heuristics, people make judgements according to the degree to which a specific description corresponds to a broader category within their minds.

Conjunction fallacy describes how conjunction is judged to be more probable than a single component descriptor. In people’s mind, sometimes conjunction appears more representative than component descriptor. Intuitively thinking, something appears to be more correct.


Assume several descriptions in order of the probability that they describe Linda. (1) She is a teacher in an elementary school. (2) She works in a book store and takes yoga classes. (3) She is active in a feminist movement. (4) She is a psychiatric social worker. (5) She is member of League of Women Voters. (6) She is a bank teller. (7) She is an insurance salesperson. (8) She is a bank teller who is active in activist movement

False probabilities allocations can be triggered by greater availability of conjunction than of its unique descriptors. Conjunction creates more intuitive matches with vivid events and acts than a component of that conjunction. Thus, conjunction is likely to be perceived falsely as more probable than the component. Conjunction fallacy leads us to poorly predict outcomes which makes us ill prepared to cope with unanticipated events.

Adapted from

Bazerman, M.H. and Moore, D.A., 1994. Judgment in managerial decision making (p. 226). New York: Wiley.

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