Typical Reasoning
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Experiment Summary
On each trial the participant was given a brief description of a person, and then asked to judge how likely (on a scale of 0 to 7) it was that the person has a particular job or hobby. The higher the rating, the more likely.
Independent Variable(s)
There were two independent variables: whether the activity is typical or atypical for a person's occupation, and whether there was one or two activities.
Dependent Measure(s)
The rating (0 to 7) the participant gave.
Expected Results
For single events, participants gave higher ratings for the typical event than for the atypical event. For the conjunctions, participants gave higher ratings for the typical than for the atypical conjunction. Participants also rated conjuctions with typical activities as more likely than single typical events. When relying on objective probabilities, the conjunctions were rated as less likely than the single events, because it should be less likely that two events occur than just one of those events.
Theoretical Significance
Tversky and Kahneman (1983) are well known for their research showing that people's estimates of probability are often very different from the objective probabilities. The reason, they argue, is that people often use heuristics to help them estimate the answer. Heuristics can be seen as sacrificing some accuracy for an increase in speed. By using heuristics, people can very quickly come up with an answer that is usually good enough for day to day purposes. These heuristics, however, can lead to incorrect judgments.
One of the most striking errors is known as the conjunction fallacy. In its most simple form, it says that people think that having both A and B occur is more likely than having just A occur or just B occur. According to objective probabilities, the probability of two events occuring has to be less than the probabilities of either of the events happening by themselves. In some circumstances, however, people are more likely to say the conjunction (having both events occur) is more likely.
