消费者偏好PPT课件教材讲义

ChapterThreePreferences消费者偏好WhereAreWeintheCourse?

Wearestudyingthe1stofthethreeblocksofmicroeconomics:Consumerbehavior,productiontheory,andmarketequilibriumWithinthe1stblock,weareworkingonthe2ndofthethreecomponents:choiceset,preference,andconsumerdemandWhatDoWeMeanbyPreference?(偏好)

Itreferstotheorderedrelationshipamongalternativechoicesgivenbyaneconomicagent.Inmosteconomicliterature,consumerpreferenceistreatedastheultimateexogenouselement.PreferenceRelationsComparingtwodifferentconsumptionbundles,xandy:strictpreference:xismorepreferredthanisy.weakpreference:xisasatleastaspreferredasisy.Indifference:xisexactlyaspreferredasisy.Notations

denotesstrictpreference;

~denotesindifference;denotesweakpreference;

p~fwww.ZQZL.cn中国最庞大的数据库下载PreferenceRelationsxyandyximplyx~y.xyand(notyx)implyxy.~f~f~f~fpAssumptionsaboutPreferenceRelationsCompleteness:Foranytwobundlesxandyitisalwayspossibletomakethestatementthateither

xy

or

yx.~f~fAssumptionsaboutPreferenceRelationsReflexivity:Anybundlexisalwaysatleastaspreferredasitself;i.e.

xx.~fAssumptionsaboutPreferenceRelationsTransitivity:If

xisatleastaspreferredasy,and

yisatleastaspreferredasz,then

xisatleastaspreferredasz;i.e.

xyandyzxz.~f~f~fIndifferenceCurves

无差异曲线(或,无差异集)Takeareferencebundlex’.Thesetofallbundlesequallypreferredtox’istheindifferencecurvecontainingx’;thesetofallbundlesy~x’.Sinceanindifference“curve”isnotalwaysacurveabetternamemightbeanindifference“set”.IndifferenceCurvesx2x1x”x”’x’~x”~x”’x’IndifferenceCurvesx2x1z

x

yppxyzIndifferenceCurvesx2x1xAllbundlesinI1arestrictlypreferredtoallinI2.yzAllbundlesinI2arestrictlypreferredto

allinI3.I1I2I3IndifferenceCurvesx2x1WP(x),thesetof

bundlesweaklypreferredtox.

WP(x)

includes

I(x).xI(x)IndifferenceCurvesx2x1SP(x),thesetof

bundlesstrictlypreferredtox,

doesnot

includeI(x).xI(x)IndifferenceCurvesCannotIntersect!(不相交!)x2x1xyzI1I2FromI1,x~y.FromI2,x~z.Thereforey~z.IndifferenceCurvesCannotIntersect

x2x1xyzI1I2FromI1,x~y.FromI2,x~z.Thereforey~z.ButfromI1andI2weseeyz,a

contradiction.pSlopesofIndifferenceCurvesWhenmoreofacommodityisalwayspreferred,thecommodityisagood.Ifeverycommodityisagoodthenindifferencecurvesarenegativelysloped.SlopesofIndifferenceCurvesBetterWorseGood2Good1Twogoods

anegativelyslopedindifferencecurve.SlopesofIndifferenceCurvesIflessofacommodityisalwayspreferredthenthecommodityisabad.SlopesofIndifferenceCurvesBetterWorseGood2Bad1Onegoodandone

badapositivelyslopedindifferencecurve.ExtremeCasesofIndifferenceCurves;PerfectSubstitutesIfaconsumeralwaysregardsunitsofcommodities1and2asequivalent,thenthecommoditiesareperfectsubstitutesandonlythesum

ofthetwocommoditiesinbundlesdeterminestheirpreferencerank-order.ExtremeCasesofIndifferenceCurves;PerfectSubstitutesx2x1881515Slopesareconstantat-1.I2I1BundlesinI2allhaveatotal

of15unitsandarestrictlypreferredtoallbundlesin

I1,whichhaveatotalof

only8unitsinthem.ExtremeCasesofIndifferenceCurves;PerfectComplementsIfaconsumeralwaysconsumescommodities1and2infixedproportion(e.g.one-to-one),thenthecommoditiesareperfectcomplementsandonlythenumberofpairsofunitsofthetwocommoditiesdeterminesthepreferencerank-orderofbundles.ExtremeCasesofIndifferenceCurves;PerfectComplementsx2x1I2I145o5959Sinceeachof(5,5),(5,9)and(9,5)contains5pairs,eachislesspreferredthanthebundle(9,9)

whichcontains9pairs.

PreferencesExhibitingSatiationAbundlestrictlypreferredtoanyotherisasatiationpointorablisspoint.Whatdoindifferencecurveslooklikeforpreferencesexhibitingsatiation?IndifferenceCurvesExhibitingSatiationx2x1BetterBetterBetterSatiation

(bliss)

pointIndifferenceCurvesforDiscreteCommoditiesAcommodityisinfinitelydivisibleifitcanbeacquiredinanyquantity;e.g.waterorcheese.Acommodityisdiscreteifitcomesinunitlumpsof1,2,3,…andsoon;e.g.aircraft,shipsandrefrigerators.IndifferenceCurvesforDiscreteCommodities

(studythisyourself)Supposecommodity2isaninfinitelydivisiblegood(gasoline)whilecommodity1isadiscretegood(aircraft).Whatdoindifference“curves”looklike?IndifferenceCurvesWithaDiscreteGood

(studythisyourself)Gas-olineAircraft01234Indifference“curves”

arecollectionsof

discretepoints.Well-BehavedPreferencesApreferencerelationis“well-behaved”ifitismonotonicandconvex.Monotonicity:Moreofanycommodityisalwayspreferred(i.e.nosatiationandeverycommodityisagood).Well-BehavedPreferencesConvexity(凸性):Mixturesofbundlesare(atleastweakly)preferredtothebundlesthemselves.E.g.,the50-50mixtureofthebundlesxandyis

z=(0.5)x+(0.5)y.

zisatleastaspreferredasxory.Well-BehavedPreferences--Convexity.x2y2x1y1xyz=(tx1+(1-t)y1,tx2+(1-t)y2)ispreferredtoxandyforall0<t<1.Well-BehavedPreferences--Convexity.x2y2x1y1xyPreferencesarestrictlyconvex

whenallmixturesz

arestrictly

preferredtotheir

component

bundlesxandy.zWell-BehavedPreferences--WeakConvexity.x’y’z’Preferencesareweaklyconvexifatleastonemixturezisequallypreferredtoacomponentbundle.xzyNon-ConvexPreferencesx2y2x1y1zBetterThemixturez

islesspreferredthanxory.MoreNon-ConvexPreferencesx2y2x1y1zBetterThemixturez

islesspreferredthanxory.MarginalRate-of-Substitution

(边际替代率)Theslopeofanindifferencecurveisitsmarginalrate-of-substitution(MRS)(边际替代率)HowcanaMRSbecalculated?MarginalRateofSubstitutionx2x1x’MRSatx’istheslopeofthe

indifferencecurveatx’MarginalRateofSubstitutionx2x1

MRSatx’is

lim{Dx2/Dx1}

Dx10

=dx2/dx1atx’Dx2Dx1x’MarginalRateofSubstitutionx2x1dx2dx1dx2=MRS´dx1so,atx’,MRSistherateatwhichtheconsumerisonlyjustwillingtoexchangecommodity2forasmallamountofcommodity1.x’MRS&Ind.CurvePropertiesBetterWorseGood2Good1Twogoods

anegativelyslopedindifferencecurveMRS<0.MRS&Ind.CurvePropertiesBetterWorseGood2Bad1Onegoodandone

badapositivelyslopedindifferencecurveMRS>0.MRS&Ind.CurvePropertiesGood2Good1