Representativeness Heuristic - Consequences of Rule Violation

Consequences of Rule Violation

The representativeness heuristic violates one of the fundamental properties of probability: extensionality. For example, participants were provided with a description of Linda who resembles a feminist. Then participants were asked to evaluate the probability of her being a feminist, the probability of her being a bank teller, or the probability of being both a bank teller and feminist. Probability theory dictates that the probability of being both a bank teller and feminist (the conjunction of two sets) must be less than or equal to the probability of being either a feminist or a bank teller. However, participants judged the conjunction (bank teller and feminist) as being more probable than being a bank teller alone.

The use of the representativeness heuristic will likely lead to violations of Bayes' Theorem. Bayes' Theorem states:

However, judgments by representativeness only look at the resemblance between the hypothesis and the data, thus inverse probabilities are equated:

As can be seen, the base rate P(H) is ignored in this equation, leading to the base rate fallacy. This was explicitly tested by Dawes, Mirels, Gold and Donahue (1993) who had people judge both the base rate of people who had a particular personality trait and the probability that a person who had a given personality trait had another one. For example, participants were asked how many people out of 100 answered true to the question "I am a conscientious person" and also, given that a person answered true to this question, how many would answer true to a different personality question. They found that participants equated inverse probabilities (e.g., ) even when it was obvious that they were not the same (the two questions were answered immediately after each other).