Linda is single, outspoken and deeply engaged with social issues. Which of the following is more likely? That Linda is a bank manager: or that Linda is a bank manager who is an active feminist?
This is one of the best-known problems in behavioural economics. Many people say that the second option is more likely. Yet, the standard response goes, this cannot be. The rules of probability tell us the probability that both A and B are true cannot exceed the probability that either A or B is true. It is less likely that someone is a female Jamaican Olympic gold medallist than that a person is female, or that a person is Jamaican, or that a person is a gold medallist. Yet even people trained in probability make a mistake with the Linda problem.
Or is it a mistake? Little introspection is required to understand what is going on. Respondents do not interpret the question as one about probability. They think it is a question about believability. The description of Linda that ends with the statement “Linda is a bank manager” is designed to be incongruous. The addition – “and an active feminist” begins to restore coherence. The story becomes more believable, even if less probable. No one gets the Jamaican problem wrong because every part of the story makes sense.