heuristics and biases

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1、±±±±±±±±±±±±±±±±±±±±±±±CHAPTERHEURISTICSANDBIASES±±±±±±5±±±±±5.1INTRODUCTIONOnecriticismthatisleviedagainsttraditionalmodelsineconomicsandfinanceisthattheyaresometimesformulatedasifthetypicaldecision-makerwereanindi-vidualwithunlimitedcerebralRAM.Suchadecision-makerwouldconsiderallrel-evantinformati

2、onandcomeupwiththebestchoiceunderthecircumstancesinaprocessknownasconstrainedoptimization.Normalhumansareimperfectandinformationrequirementsareforsomemodelsegregious.Areweaskingtoomuch?Takethecapitalassetpricingmodel(CAPM),amodelfamousandimportantenoughthatWilliamSharpewonthe1990NobelPrizeforEconomi

3、cSciencesforthiscontribution.Thismodelassumesthatinvestorsarecapableofstudyingtheuniverseofsecuritiesinordertocomeupwithallrequiredmodelinputs.Theseinputsincludeexpectedreturnsandvariancesforallsecurities,aswellascovariancesamongallsecurities.Onlythenistheinves-torabletomakeappropriateportfoliodecis

4、ions.Thischapterfocusesonhowpeoplemakedecisionswithlimitedtimeandinformationinaworldofuncertainty.Itbeginsinthenextsectionbydiscussingcertaincognitivelimitationsthatmayrendertheexpectationsofsomemodelsun-reasonable.Perceptionandmemoryareimprecisefiltersofinformation,andthewayinwhichinformationispres

5、ented,thatis,theframe,influenceshowitisre-ceived.Becausetoomuchinformationisdifficulttodealwith,peoplehavedevel-opedshortcutsorheuristicsinordertocomeupwithreasonabledecisions.Unfortunately,sometimestheseheuristicsleadtobias,especiallywhenusedoutsidetheirnaturaldomains.Aclassofheuristicsimpactingpre

6、ferencesprimarilyviacomfort-seekingisdiscussedinSection5.3.InSection5.4,wediscussseveralheur-isticsdesignedtoestimateprobability.Themostimportantoftheseisrepresenta-tivenessinitsvariousmanifestations.Inthenextsection,weturntoanchoring,thetendencytochangeone’sviewmoreslowlythanisappropriate.Section5.

7、6dis-cussesamajorcritiqueoftheheuristicsandbiasesprogram,theso-called“fastandfrugal”heuristicsviewthatarguesthatheuristicsactuallyworksurprisinglywell.8384CHAPTER5Finally,inthelastsection,welookaheadt