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RiskandUncertaintyII BenjaminChiao March31,2011(afterclassversion)LectureNotesforUndergraduate LevelInformationEconomics,ShanghaiUniversityofFinanceand Economics 1/19 IDe…nitionsofRiskAttitudes IMeasurementofRiskAttitudes IComparisonofDistributions 2/19 IDe…nitionsofRiskAttitudes ! IMeasurementofRiskAttitudes IComparisonofDistributions 3/19 IDe…nitionsofRiskAttitudes ! 4/19 RiskAversev.RiskLoving ISetting IMonetaryoutcomes.Denotemoneyasacontinuousrandom variablexdistributedaccordingtothecumulativedistribution functionF(x). IThelotteryspaceisallpossiblec.d.fovernonnegative amountofmoneyL ISothecontinuousversionoftheEUtheoremgives: U(F)=u(x)dF(x)(1) Z ITheBernoulliutilityfunctionu(x)isassumedtobeincreasing andcontinuous. IAndalsoboundedness(referstotheSt.Petersburg-Menger paradox) 5/19 RiskAttitudeDe…nitions IDe…nitionArisklovingpersonweaklyprefersalotteryF() overthelotterythatgivesasureoutcomehavingthevalue thesameastheexpectedvaluexdF(x). IIfthepersonisindi¤erent,he’scalledRriskneutral IIfthepersonpreferstheotherdirection,he’scalledriskaverse IIntheexpectedutilitycontext,itfollowsfromtheabovethata riskaversepersonsatis…estheJensen’sinequality(orconcavity ofu): F:u(x)dF(x)u(xdF(x))(2) 8ZZ ISeeFigure. 6/19 IDe…nition ICertaintyequivalentc(F,u)istheamountofmoneythat satis…es u(x)dF(x)=u(c(F,u))(3) Z IThatis,youareindi¤erenttotakingcorthegambleF. ISeeFig. IExercise1:Provethatapersonisriskaversei¤ c(F,u)xdF(x)  R 7/19 IDe…nition IProbabilitypremiumπ(x,e,u)istheprobabilitythatsatis…es, foralle>0, 11 u(x)=(+π(x,e,u))u(x+e)+(π(x,e,u))u(xe) 22 IGivenasureoutcomex,theprobabilitypremiumπ(x,e,u)is theprobabilityyouwouldsubstractfrom1/2ofprobabilityof gettingaslightlyworseo¤outcome(xe)andaddtoa1/2 probabilityofgettingaslightlybettero¤outcome(x+e)so thatyouareindi¤erentbetweenthisandx. ISeeFig. IExercise2:Provethatapersonisriskaversei¤π(x,e,u)0  8/19 IDe…nitionsofRiskAttitudes IMeasurementofRiskAttitudes ! IComparisonofDistributions 9/1