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In expected utility theory, a lottery is a discrete distribution of probability on a set of ''states of nature''. The elements of a lottery correspond to the probability that a certain outcome arises from a given state of nature.〔Mas-Colell, Andreu, Michael Whinston and Jerry Green (1995). ''Microeconomic theory''. Oxford: Oxford University Press. ISBN 0-19-507340-1〕 In economics, individuals are assumed to rank lotteries according to a rational system of preferences, although it is now accepted that people make irrational choices systematically. Behavioral economics studies what happens in markets in which some of the agents display human complications and limitations.〔Mullainathan, Sendhil., & Thaler, Richard. (2000). 'Behavioral Economics'. NBER Working Paper No. 7948, p. 2.〕 == Choice under risk == According to Expected Utility Theory, people choose among risky alternatives or scenarios using a criterion that combines three dimensions: the subjective estimate of the probabilities of the possible outcomes, the gambling preferences, and the ranking of prizes and penalties. The combination of the last two dimensions is made through a utility attached to them by a function called Bernoulli utility. Then this abstract measure is combined with the dimension of subjective probabilities exactly through a linear combination of each of these Bernoulli utilities. The weights for these linear combination are the subjective probabilities. For example, let there be three states of nature, "beautiful and eventful trip by car", "staying home", and "death by car accident". Their consequences and bernoulli utilities are: * Beautiful and eventful trip by car = $4 = 16 utils * Staying home = $3 = 9 utils * Death by car accident = $2 = 4 utils If people had to choose the best of two scenarios A and B, each of which assigns probabilities to the states of nature, how would they do it? A theory of choice under risk starts by letting people have preferences on the set of lotteries over these kind of states of nature. If preferences over lotteries are complete and transitive, they are called rational. As a result of computing the expected utility from scenarios A and B, rational people should pick the one with the highest expected utility. Rankings of alternatives made under uncertainty can be represented by Cardinal utility, but they are not Ordinal. The assumption about combining linearly the individual Bernoulli utilities and making the resulting number be the criterion to be maximized can be justified of the grounds of the independence axiom. Therefore, Expected utility theory depends on the empirical validity of the independence axiom. The preference relation satisfies independence if for any three simple lotteries p, q, r, and any number E(0,1) it holds that: if and only if Indifference maps can be represented in the simplex. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lottery (probability)」の詳細全文を読む スポンサード リンク
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