© POSbase 2005 The Conjunction Fallacy Please read the following scenario: (by Tversky & Kahneman, 1983)Tversky & Kahneman, 1983 Linda is 31 years old, single, outspoken and very bright. At university she studied philosophy. As a student she was deeply concerned with issues of discrimination and social justice and also participated in anti-nuclear demonstrations. Now rank the eight statements on the following slide from most to least likely. For the most likely statement enter 1, for the most likely of the remaining seven statements enter 2, and so forth, and for the least likely statement enter 8. Contributor

© POSbase 2005 The Conjunction Fallacy Linda is a teacher in elementary school. Linda works in a bookstore and takes Yoga classes. Linda is active in the feminist movement. Linda is a psychiatric social worker. Linda is a member of the League of Woman Voters. Linda is a bank teller. Linda is an insurance salesperson. Linda is a bank teller and is active in the feminist movement. (1 = most likely, 8 = least likely)

© POSbase 2005 As can be seen, the conjunctive probability that Linda is both a bank teller and active in the feminist movement is necessarily smaller or equal the probability that Linda is a bank teller. Violating this conjunction rule, 85% of the participants in Tversky and Kahneman‘s original study ranked „ Linda is a bank teller and is active in the feminist movement“ higher than „Linda is a bank teller“. The Conjunction Fallacy Linda is a bank teller and is active in the feminist movement Linda is a bank teller Linda is active in the feminist movement

© POSbase 2005 Violating this conjunction rule, 85% of the participants in Tversky and Kahneman‘s original study ranked „ Linda is a bank teller and is active in the feminist movement“ higher than „Linda is a bank teller“. The Conjunction Fallacy

© POSbase 2005 The authors explained this violation of a normative rule in terms of the representativeness heuristic, but other explanations have been put forward, such as: Linguistic misunderstandings (Morrier & Borgida, 1984); Signed summation (Yates & Carlson, 1986); Frequentist interpretations (Fiedler, 1988);Fiedler, 1988 Applying the wrong probabilistic rule (Wolford et al., 1990); Mental models (Johnson-Laird et al., 1999). The Conjunction Fallacy