Conjunction Fallacy

If you don't simplify your assumptions, you can fall into a couple of traps, described in our next mental models. First, most people are, unfortunately, hardwired to latch onto unnecessary assumptions, a predilection called the conjunction fallacy, studied by Amos Tversky and Daniel Kahneman, who provided this example in the October 1983 Psychological Review: Linda is 31 years old, single, outspoken, and very bright. She majored in philosophy. As a student, she was deeply concerned with issues of discrimination and social justice, and also participated in anti-nuclear demonstrations. Which is more probable? 1. Linda is a bank teller. 2. Linda is a bank teller and is active in the feminist movement. In their study, most people answered that number 2 is more probable, but that's impossible unless all bank tellers are also active in the feminist movement. The fallacy arises because the probability of two events in conjunction is always less than or equal to the probability of either one of the events occurring alone, a concept illustrated in the Venn diagram on the next page.