Conjuction Error Conjunction Fallacy Examine the following personality

Conjuction Error

• Conjunction Fallacy • Examine the following personality sketch: • Bill is 34 years old. He is intelligent, but • • • unimaginative, compulsive and generally lifeless. In school, he was strong in mathematics but weak in social studies and humanities. Which statement is more probable: A. Bill is an accountant that plays jazz for a hobby, or B. Bill plays jazz for a hobby?

Conjunction Fallacy solution • From elementary probability theory, the probability of a conjunction P(Accountant + Jazz) cannot exceed the probability of either of its constituents, P(Accountant) or P(Jazz). This is the conjunction rule. However, it is often the case that the conjunction is more representative of its class than either of its constituents, or more available in some way, and therefore judgements of its probability are subject to one of the representativeness or availability heuristics.

• In the example, choice A was erroneously selected by 92% of subjects including those who were informed in matters of statistics.

Definition: Conjunction Fallacy • Under some circumstances people make more extreme predictions for the joint occurrence of events than for a single event that is part of the joint event. • This is an error in thinking, as a combination of events cannot occur more often than one event in the combination.