北大微观经济学课件(英文版)ch3 Preferences

2020/3/19中级微观经济学ChapterThreePreferences偏好2020/3/19中级微观经济学StructureDescribepreferencesIndifferencecurves(无差异曲线)Well-behavedpreferencesMarginalrateofsubstitution(边际替代率)2020/3/19中级微观经济学RationalityinEconomicsBehavioralPostulate:Adecisionmakeralwayschoosesitsmostpreferredalternativefromitssetofavailablealternatives.Sotomodelchoicewemustmodeldecision-makers’preferences.2020/3/19中级微观经济学PreferenceRelationsComparingtwodifferentconsumptionbundles,xandy:–strictpreference(严格偏好):xismorepreferredthanisy(xy).–Indifference(无差异):xisexactlyaspreferredasisy(x~y).–weakpreference(弱偏好):xisasatleastaspreferredasisy(xy).p~f2020/3/19中级微观经济学PreferenceRelationsPreferencerelationsareordinalrelations;i.e.theystateonlytheorderinwhichbundlesarepreferred.2020/3/19中级微观经济学PreferenceRelationsxyandyximplyx~y.~f~f2020/3/19中级微观经济学PreferenceRelationsxyandyximplyx~y.xyand(notyx)implyxy.~f~f~f~fp2020/3/19中级微观经济学AssumptionsaboutPreferenceRelationsCompleteness(完备性):Foranytwobundlesxandyitisalwayspossibletomakethestatementthateitherxyoryx.~f~f2020/3/19中级微观经济学AssumptionsaboutPreferenceRelationsReflexivity(反身性):Anybundlexisalwaysatleastaspreferredasitself;i.e.xx.~f2020/3/19中级微观经济学AssumptionsaboutPreferenceRelationsTransitivity(传递性):Ifxisatleastaspreferredasy,andyisatleastaspreferredasz,thenxisatleastaspreferredasz;i.e.xyandyzxz.~f~f~f2020/3/19中级微观经济学IndifferenceCurvesTakeareferencebundlex’.Thesetofallbundlesequallypreferredtox’istheindifferencecurvecontainingx’;thesetofallbundlesy~x’.Sinceanindifference“curve”isnotalwaysacurveabetternamemightbeanindifference“set”.2020/3/19中级微观经济学IndifferenceCurvesx2x1x”x”’x’~x”~x”’x’2020/3/19中级微观经济学IndifferenceCurvesx2x1zxyppxyz2020/3/19中级微观经济学IndifferenceCurvesx2x1xAllbundlesinI1arestrictlypreferredtoallinI2.yzAllbundlesinI2arestrictlypreferredtoallinI3.I1I2I32020/3/19中级微观经济学x2x1I(x’)xI(x)WP(x),thesetofbundlesweaklypreferredtox.WeaklyPreferredSet(弱偏好集)2020/3/19中级微观经济学WeaklyPreferredSet(弱偏好集)x2x1WP(x),thesetofbundlesweaklypreferredtox.WP(x)includesI(x).xI(x)2020/3/19中级微观经济学StrictlyPreferredSet(严格偏好集)x2x1SP(x),thesetofbundlesstrictlypreferredtox,doesnotincludeI(x).xI(x)2020/3/19中级微观经济学IndifferenceCurvesCannotIntersectx2x1xyzI1I2FromI1,x~y.FromI2,x~z.Thereforey~z.ButfromI1andI2weseeyz,acontradiction.p2020/3/19中级微观经济学SlopesofIndifferenceCurvesWhenmoreofacommodityisalwayspreferred,thecommodityisagood.Ifeverycommodityisagoodthenindifferencecurvesarenegativelysloped.2020/3/19中级微观经济学SlopesofIndifferenceCurvesGood2Good1Twogoodsanegativelyslopedindifferencecurve.2020/3/19中级微观经济学SlopesofIndifferenceCurvesIflessofacommodityisalwayspreferredthenthecommodityisabad.2020/3/19中级微观经济学SlopesofIndifferenceCurvesGood2Bad1Onegoodandonebadapositivelyslopedindifferencecurve.2020/3/19中级微观经济学ExamplesPerfectsubstitutes(完全替代)Perfectcomplements(完全互补)Satiation(餍足)Discretegoods(离散商品)2020/3/19中级微观经济学ExtremeCasesofIndifferenceCurves;PerfectSubstitutesIfaconsumeralwaysregardsunitsofcommodities1and2asequivalent,thenthecommoditiesareperfectsubstitutesandonlythetotalamountofthetwocommoditiesinbundlesdeterminestheirpreferencerank-order.2020/3/19中级微观经济学ExtremeCasesofIndifferenceCurves;PerfectSubstitutesx2x1881515Slopesareconstantat-1.I2I1BundlesinI2allhaveatotalof15unitsandarestrictlypreferredtoallbundlesinI1,whichhaveatotalofonly8unitsinthem.2020/3/19中级微观经济学ExtremeCasesofIndifferenceCurves;PerfectComplementsIfaconsumeralwaysconsumescommodities1and2infixedproportion(e.g.one-to-one),thenthecommoditiesareperfectcomplementsandonlythenumberofpairsofunitsofthetwocommoditiesdeterminesthepreferencerank-orderofbundles.2020/3/19中级微观经济学ExtremeCasesofIndifferenceCurves;PerfectComplementsx2x1I145o5959Eachof(5,5),(5,9)and(9,5)contains5pairssoeachisequallypreferred.2020/3/19中级微观经济学ExtremeCasesofIndifferenceCurves;PerfectComplementsx2x1I2I145o5959Sinceeachof(5,5),(5,9)and(9,5)contains5pairs,eachislesspreferredthanthebundle(9,9)whichcontains9pairs.2020/3/19中级微观经济学PreferencesExhibitingSatiationAbundlestrictlypreferredtoanyotherisasatiationpointorablisspoint.Whatdoindifferencecurveslooklikeforpreferencesexhibitingsatiation?2020/3/19中级微观经济学IndifferenceCurvesExhibitingSatiationx2x1Satiation(bliss)point2020/3/19中级微观经济学IndifferenceCurvesExhibitingSatiationx2x1BetterSatiation(bliss)point2020/3/19中级微观经济学IndifferenceCurvesExhibitingSatiationx2x1BetterSatiation(bliss)point2020/3/19中级微观经济学IndifferenceCurvesforDiscreteCommoditiesAcommodityisinfinitelydivisibleifitcanbeacquiredinanyquantity;e.g.waterorcheese.Acommodityisdiscreteifitcomesinunitlumpsof1,2,3,…andsoon;e.g.aircraft,shipsandrefrigerators.2020/3/19中级微观经济学IndifferenceCurvesforDiscreteCommoditiesSupposecommodity2isaninfinitelydivisiblegood(gasoline)whilecommodity1isadiscretegood(aircraft).Whatdoindifference“curves”looklike?2020/3/19中级微观经济学IndifferenceCurvesWithaDiscreteGoodGas-olineCar01234Indifference“curves”arecollectionsofdiscretepoints.2020/3/19中级微观经济学Well-BehavedPreferencesApreferencerelationis“well-behaved”ifitis–Monotonic(单调)andconvex(凸状).Monotonicity:Moreofanycommodityisalwayspreferred(i