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The probabilities of unique events
Sangeet S Khemlani1, Max Lotstein, Phil Johnson-Laird
1Navy Center for Applied Research in Artificial Intelligence, Naval Research Lab, Washington, District of Columbia, United States of America. skhemlani@gmail.com
Plos One
|October 12, 2012
Summary
Estimating probabilities for unique events is challenging. This study introduces a theory where intuitive and deliberative systems influence probability judgments, leading to predictable errors in conjunction probability estimates.
Area of Science:
- Cognitive Psychology
- Decision Science
- Probability Theory
Background:
- The probability of unique events is often considered meaningless by theorists.
- Psychological investigation into estimating probabilities of unique events is limited.
- Existing models do not fully capture how individuals estimate probabilities of singular occurrences.
Purpose of the Study:
- To propose and test a new theory of probability estimation for unique events.
- To investigate the interplay between intuitive and deliberative cognitive systems in probability judgment.
- To explain systematic biases in estimating conjunction probabilities.
Main Methods:
- Development of a computational model simulating intuitive and deliberative estimation processes.
- Conducting two experiments to observe human probability judgments.
- Analyzing verbal and numerical probability estimates for violations of probability calculus.
Main Results:
- Individuals tend to "split the difference" when estimating conjunction probabilities, deviating from normative rules.
- These systematic errors persist even when individuals provide non-numerical, qualitative probability estimates.
- Experimental findings corroborate the predictions of the proposed dual-system theory.
Conclusions:
- Probability estimation for unique events is influenced by a dual cognitive system: an intuitive, non-numerical component and a deliberative, numerical component.
- The theory provides a framework for understanding systematic biases in probability judgments, particularly for conjunctions.
- Further research can explore the parameters of these intuitive and deliberative systems in various contexts.
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