The probabilities of unique events.
Many theorists argue that the probabilities of unique events, even real possibilities such as President Obama's re-election, are meaningless. As a consequence, psychologists have seldom investigated them. We propose a new theory (implemented in a computer program) in which such estimates depend on an intuitive non-numerical system capable only of simple procedures, and a deliberative system that maps intuitions into numbers. The theory predicts that estimates of the probabilities of conjunctions should often tend to split the difference between the probabilities of the two conjuncts. We report two experiments showing that individuals commit such violations of the probability calculus, and corroborating other predictions of the theory, e.g., individuals err in the same way even when they make non-numerical verbal estimates, such as that an event is highly improbable.
Navy Center for Applied Research in Artificial Intelligence, Naval Research Lab, Washington, District of Columbia, United States of America. skhemlani@gmail.com
Sangeet S
SS
Khemlani
Max
M
Lotstein
Phil
P
Johnson-Laird
D002755:Choice Behavior; D003198:Computer Simulation; D003657:Decision Making; D006801:Humans; D008960:Models, Psychological; D011336:Probability; D011338:Probability Theory; D012984:Software