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1、ChapterThreePreferences偏好RoadMap•Describepreferences•Indifferencecurves(无差异曲线)•Well-behavedpreferences•Marginalrateofsubstitution(边际替代率)RationalityinEconomics•BehavioralPostulate:Adecision-makeralwayschoosesitsmostpreferredalternativefromitssetofavailablealternatives.•Sotomodel
2、choicewemustmodeldecision-makers’preferences.PreferenceRelations•Comparingtwodifferentconsumptionbundles,xandy:–strictpreference(严格偏好):xismoreπpreferredthanisy(xy).–Indifference(无差异):xisexactlyaspreferredasisy(x~y).–weakpreference(弱偏好):xisasatleastaspreferredasisy(xy).φ~Prefere
3、nceRelations•Preferencerelationsareordinalrelations;i.e.theystateonlytheorderinwhichbundlesarepreferred.PreferenceRelations•xyandyximplyxφφ∼y.~~PreferenceRelations•xyandyximplyxφφ∼y.~~π•xyand(notyx)implyxy.φφ~~AssumptionsaboutPreferenceRelations•Completeness(完备性):Foranytwobundl
4、esxandyitisalwayspossibletomakethestatementthateitherxyφor~yx.φ~AssumptionsaboutPreferenceRelations•Reflexivity(反身性):Anybundlexisalwaysatleastaspreferredasitself;i.e.xx.φ~AssumptionsaboutPreferenceRelations•Transitivity(传递性):Ifxisatleastaspreferredasy,andyisatleastaspreferredas
5、z,thenxisatleastaspreferredasz;i.e.xyandyzxz.φφφ~~~CounterExample•A,B,C,=>x,y,z,•A:xyzφ~φ~•B:yzxφ~φ~•C:zxyφ~φ~•Votingsystem:•xy,yz,zx.φφ~φ~~IndifferenceCurves•Takeareferencebundlex’.Thesetofallbundlesequallypreferredtox’istheindifferencecurvecontainingx’;thesetofallbundlesy∼x’.
6、•Sinceanindifference“curve”isnotalwaysacurveabetternamemightbeanindifference“set”.IndifferenceCurvesxx2xx’’∼∼xx””∼∼xx”’”’x’xx””xx”’”’xx1IndifferenceCurvesππxx2zzxxyyxzyxx1IndifferenceCurvesI1AllbundlesinIare1x2xstrictlypreferredtoallinI.2zI2AllbundlesinIare2ystrictlypreferredto
7、I3allinI.3x1WeaklyPreferredSet(弱偏好集)x2WP(x),thesetofxbundlesweaklypreferredtox.I(x)I(x’)x1WeaklyPreferredSet(弱偏好集)x2WP(x),thesetofxbundlesweaklypreferredtox.WP(x)includesI(x)I(x).x1StrictlyPreferredSet(严格偏好集)x2SP(x),thesetofxbundlesstrictlypreferredtox,doesnotincludeI(x)I(x).x1
8、IndifferenceCurvesCannotIntersectxx2I2FromIFromI1,x,x∼
