《微观经济学》清华大学课件 Ch3 Preferences消费者偏好.ppt

ChapterThree Preferences消费者偏好 WhereAreWeintheCourse Wearestudyingthe1stofthethreeblocksofmicroeconomics Consumerbehavior productiontheory andmarketequilibriumWithinthe1stblock weareworkingonthe2ndofthethreecomponents choiceset preference andconsumerdemand WhatDoWeMeanbyPreference 偏好 Itreferstotheorderedrelationshipamongalternativechoicesgivenbyaneconomicagent Inmosteconomicliterature consumerpreferenceistreatedastheultimateexogenouselement PreferenceRelations Comparingtwodifferentconsumptionbundles xandy strictpreference xismorepreferredthanisy weakpreference xisasatleastaspreferredasisy Indifference xisexactlyaspreferredasisy Notations denotesstrictpreference denotesindifference denotesweakpreference p PreferenceRelations xyandyximplyx y xyand notyx implyxy p AssumptionsaboutPreferenceRelations Completeness Foranytwobundlesxandyitisalwayspossibletomakethestatementthateitherxyoryx AssumptionsaboutPreferenceRelations Reflexivity Anybundlexisalwaysatleastaspreferredasitself i e xx AssumptionsaboutPreferenceRelations Transitivity Ifxisatleastaspreferredasy andyisatleastaspreferredasz thenxisatleastaspreferredasz i e xyandyzxz IndifferenceCurves无差异曲线 或 无差异集 Takeareferencebundlex Thesetofallbundlesequallypreferredtox istheindifferencecurvecontainingx thesetofallbundlesy x Sinceanindifference curve isnotalwaysacurveabetternamemightbeanindifference set IndifferenceCurves x2 x1 x x x x x x IndifferenceCurves x2 x1 zxy p p x y z IndifferenceCurves x2 x1 x AllbundlesinI1arestrictlypreferredtoallinI2 y z AllbundlesinI2arestrictlypreferredtoallinI3 I1 I2 I3 IndifferenceCurves x2 x1 WP x thesetofbundlesweaklypreferredtox WP x includesI x x I x IndifferenceCurves x2 x1 SP x thesetofbundlesstrictlypreferredtox doesnotincludeI x x I x IndifferenceCurvesCannotIntersect 不相交 x2 x1 x y z I1 I2 FromI1 x y FromI2 x z Thereforey z IndifferenceCurvesCannotIntersect x2 x1 x y z I1 I2 FromI1 x y FromI2 x z Thereforey z ButfromI1andI2weseeyz acontradiction p SlopesofIndifferenceCurves Whenmoreofacommodityisalwayspreferred thecommodityisagood Ifeverycommodityisagoodthenindifferencecurvesarenegativelysloped SlopesofIndifferenceCurves Better Worse Good2 Good1 Twogoodsanegativelyslopedindifferencecurve SlopesofIndifferenceCurves Iflessofacommodityisalwayspreferredthenthecommodityisabad SlopesofIndifferenceCurves Better Worse Good2 Bad1 Onegoodandonebadapositivelyslopedindifferencecurve ExtremeCasesofIndifferenceCurves PerfectSubstitutes Ifaconsumeralwaysregardsunitsofcommodities1and2asequivalent thenthecommoditiesareperfectsubstitutesandonlythesumofthetwocommoditiesinbundlesdeterminestheirpreferencerank order ExtremeCasesofIndifferenceCurves PerfectSubstitutes x2 x1 8 8 15 15 Slopesareconstantat 1 I2 I1 BundlesinI2allhaveatotalof15unitsandarestrictlypreferredtoallbundlesinI1 whichhaveatotalofonly8unitsinthem ExtremeCasesofIndifferenceCurves PerfectComplements Ifaconsumeralwaysconsumescommodities1and2infixedproportion e g one to one thenthecommoditiesareperfectcomplementsandonlythenumberofpairsofunitsofthetwocommoditiesdeterminesthepreferencerank orderofbundles ExtremeCasesofIndifferenceCurves PerfectComplements x2 x1 I2 I1 45o 5 9 5 9 Sinceeachof 5 5 5 9 and 9 5 contains5pairs eachislesspreferredthanthebundle 9 9 whichcontains9pairs PreferencesExhibitingSatiation Abundlestrictlypreferredtoanyotherisasatiationpointorablisspoint Whatdoindifferencecurveslooklikeforpreferencesexhibitingsatiation IndifferenceCurvesExhibitingSatiation x2 x1 Better Better Better Satiation bliss point IndifferenceCurvesforDiscreteCommodities Acommodityisinfinitelydivisibleifitcanbeacquiredinanyquantity e g waterorcheese Acommodityisdiscreteifitcomesinunitlumpsof1 2 3 andsoon e g aircraft shipsandrefrigerators IndifferenceCurvesforDiscreteCommodities studythisyourself Supposecommodity2isaninfinitelydivisiblegood gasoline whilecommodity1isadiscretegood aircraft Whatdoindifference curves looklike IndifferenceCurvesWithaDiscreteGood studythisyourself Gas oline Aircraft 0 1 2 3 4 Indifference curves arecollectionsofdiscretepoints Well BehavedPreferences Apreferencerelationis well behaved ifitismonotonicandconvex Monotonicity Moreofanycommodityisalwayspreferred i e nosatiationandeverycommodityisagood Well BehavedPreferences Convexity 凸性 Mixturesofbundlesare atleastweakly preferredtothebundlesthemselves E g the50 50mixtureofthebundlesxandyisz 0 5 x 0 5 y zisatleastaspreferredasxory Well BehavedPreferences Convexity x2 y2 x1 y1 x y z tx1 1 t y1 tx2 1 t y2 ispreferredtoxandyforall0 t 1 Well BehavedPreferences Convexity x2 y2 x1 y1 x y Preferencesarestrictlyconvexwhenallmixtureszarestrictlypreferredtotheircomponentbundlesxandy z Well BehavedPreferences WeakConvexity x y z Preferencesareweaklyconvexifatleastonemixturezisequallypreferredtoacomponentbundle x z y Non ConvexPreferences x2 y2 x1 y1 z Better Themixturezislesspreferredthanxory MoreNon ConvexPreferences x2 y2 x1 y1 z Better Themixturezislesspreferredthanxory MarginalRate of Substitution 边际替代率 Theslopeofanindifferencecurveisitsmarginalrate of substitution MRS 边际替代率 HowcanaMRSbecalculated MarginalRateofSubstitution x2 x1 x MRSatx istheslopeoftheindifferencecurveatx MarginalRateofSubstitution x2 x1 MRSatx islim Dx2 Dx1 Dx10 dx2 dx1atx Dx2 Dx1 x MarginalRateofSubstitution x2 x1 dx2 dx1 dx2 MRS dx1so atx MRSistherateatwhichtheconsumerisonlyjustwillingtoexchangecommodity2forasmallamountofcommodity1 x MRS Ind CurveProperties Better Worse Good2 Good1 Twogoodsanegativelyslopedindifferencecurve MRS 0 MRS Ind CurveProperties Better Worse Good2 Bad1 Onegoodandonebadapositivelyslopedindifferencecurve MRS 0 MRS Ind CurveProperties Goo