ch3 现代经济学偏好.docx

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1、ChapterThreePreferences偏好RationalityinEconomics◆BehavioralPostulate:Adecisionmakeralwayschoosesitsmostpreferredalternativefromitssetofavailablealternatives.◆Sotomodelchoicewemustmodeldecision-makers’preferences.PreferenceRelations◆Preferencerelationsareordi

2、nalrelations;i.e.theystateonlytheorderinwhichbundlesarepreferred.Structure◆Describepreferences◆Indifferencecurves(无差异曲线)◆Well-behavedpreferences◆Marginalrateofsubstitution(边际替代率)PreferenceRelations◆Comparingtwodifferentconsumptionbundlesxandy:–strictprefer

3、ence(严格偏好):xis≺y).–Indifference(无差异):xisexactlyaspreferredasisy(x~y).–weakpreference(弱偏好):xisasatleastaspreferredasisy(x~y).morepreferredthanisy(xPreferenceRelations◆x~yandy~ximplyx∼y.1PreferenceRelations◆x~yandy~ximplyx∼y.◆x~yand(notx~y)implyx≺y.Assumption

4、saboutPreferenceRelations◆Reflexivity(反身性):Anybundlexisalwaysatleastaspreferredasitself;i.e.x~x.IndifferenceCurves◆Takeareferencebundlex’.Thesetofallbundlesequallypreferredtox’istheindifferencecurvecontainingx’;thesetofallbundlesy∼x’.◆Sinceanindifference“cu

5、rve”isnotalwaysacurveabetternamemightbeanindifference“set”.AssumptionsaboutPreferenceRelations◆Completeness(完备性):Foranytwobundlesxandyitisalwayspossibletomakethestatementthateitherorx~yy~x.AssumptionsaboutPreferenceRelations◆Transitivity(传递性):Ifxisatleasta

6、spreferredasyandyisatleastaspreferredaszthenxisatleastaspreferredasz;i.e.x~yandy~zx~z.IndifferenceCurvesx2x’x’∼x”∼x”’x”x”’x12IndifferenceCurvesx2xz≺x≺yzyx1IndifferenceCurvesI1AllbundlesinIarex21xstrictlypreferredtoallinI2.zI2AllbundlesinI2areyI3strictlypre

7、ferredtoallinI3.x1WeaklyPreferredSet(弱偏好集)x2WP(x)thesetofxbundlesweaklypreferredtox.I(x)I(x’)x1StrictlyPreferredSet(严格偏好集)x2SP(x),thesetofxbundlesstrictlypreferredtox,doesnotincludeI(x)I(x).x1WeaklyPreferredSet(弱偏好集)x2xWP(x),thesetofbundlesweaklypreferredt

8、ox.WP(x)includesI(x)I(x).x1IndifferenceCurvesCannotIntersectxIFromI1,x∼y.FromI2,x∼z.2I12Thereforey∼z.ButfromI1andI2weseey≺z,acontradiction.xyzx13SlopesofIndifferenceCurvesSlopesofIndifferenceCurves◆Wh