微观经济之交换.pptx

微观经济之交换.pptx

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ChapterThirty,Exchange交换,Contents,TheEdgeworth（艾奇沃斯）BoxParetoimprovingtradeParetoEfficientAllocationTheCore（核心）TradeinacompetitivemarketWalrasLawofgeneralequilibrium（一般均衡）FirstFundamentalTheoremofWelfareEconomics（福利经济学第一定理）SecondFundamentalTheoremofWelfareEconomics（福利经济学第二定理）,Exchange,Twoconsumers,AandB.Theirendowmentsofgoods1and2areE.g.Thetotalquantitiesavailable,and,and,unitsofgood1,unitsofgood2.,and,are,Exchange,EdgeworthandBowleydevisedadiagram,calledanEdgeworthbox,toshowallpossibleallocationsoftheavailablequantitiesofgoods1and2betweenthetwoconsumers.,StartinganEdgeworthBox,StartinganEdgeworthBox,Width=,StartinganEdgeworthBox,Width=,Height=,StartinganEdgeworthBox,Width=,Height=,Thedimensionsoftheboxarethequantitiesavailableofthegoods.,FeasibleAllocations,Whatallocationsofthe8unitsofgood1andthe6unitsofgood2arefeasible?

HowcanallofthefeasibleallocationsbedepictedbytheEdgeworthboxdiagram?

Onefeasibleallocationisthebefore-tradeallocation;i.e.theendowmentallocation.,Width=,Height=,Theendowmentallocationis,and,TheEndowmentAllocation,Width=,Height=,TheEndowmentAllocation,OA,OB,6,8,TheEndowmentAllocation,OA,OB,6,8,4,6,TheEndowmentAllocation,OA,OB,6,8,4,6,2,2,TheEndowmentAllocation,OA,OB,6,8,4,6,2,2,Theendowmentallocation,TheEndowmentAllocation,Moregenerally,TheEndowmentAllocation,TheEndowmentAllocation,OA,OB,Theendowmentallocation,OtherFeasibleAllocations,denotesanallocationtoconsumerA.denotesanallocationtoconsumerB.Anallocationisfeasibleifandonlyif,and,FeasibleReallocations,OA,OB,FeasibleReallocations,OA,OB,FeasibleReallocations,Allpointsinthebox,includingtheboundary,representfeasibleallocationsofthecombinedendowments.Whichallocationswillbeblockedbyoneorbothconsumers?

Whichallocationsmakebothconsumersbetteroff?

AddingPreferencestotheBox,OA,ForconsumerA.,AddingPreferencestotheBox,Morepreferred,ForconsumerA.,OA,AddingPreferencestotheBox,ForconsumerB.,OB,AddingPreferencestotheBox,Morepreferred,ForconsumerB.,OB,AddingPreferencestotheBox,Morepreferred,ForconsumerB.,OB,AddingPreferencestotheBox,OA,ForconsumerA.,AddingPreferencestotheBox,OA,OB,EdgeworthsBox,OA,OB,Pareto-Improvement,AnallocationoftheendowmentthatimprovesthewelfareofaconsumerwithoutreducingthewelfareofanotherisaPareto-improvingallocation.WherearethePareto-improvingallocations?

EdgeworthsBox,OA,OB,Pareto-Improvements,OA,OB,ThesetofPareto-improvingallocations,Pareto-Improvements,Sinceeachconsumercanrefusetotrade,theonlypossibleoutcomesfromexchangearePareto-improvingallocations.ButwhichparticularPareto-improvingallocationwillbetheoutcomeoftrade?

Pareto-Improvements,OA,OB,ThesetofPareto-improvingreallocations,Pareto-Improvements,Pareto-Improvements,Pareto-Improvements,TradeimprovesbothAsandBswelfares.ThisisaPareto-improvementovertheendowmentallocation.,Pareto-Improvements,Newmutualgains-to-traderegionisthesetofallfurtherPareto-improvingreallocations.,TradeimprovesbothAsandBswelfares.ThisisaPareto-improvement（帕累托改进）overtheendowmentallocation.,Pareto-Improvements,FurthertradecannotimprovebothAandBswelfares.,Pareto-Optimality（帕累托最优）,BetterforconsumerB,BetterforconsumerA,Pareto-Optimality,AisstrictlybetteroffbutBisstrictlyworseoff,BisstrictlybetteroffbutAisstrictlyworseoff,Pareto-Optimality,AisstrictlybetteroffbutBisstrictlyworseoff,BisstrictlybetteroffbutAisstrictlyworseoff,BothAandBareworseoff,BothAandBareworseoff,Pareto-Optimality,TheallocationisPareto-optimalsincetheonlywayoneconsumerswelfarecanbeincreasedistodecreasethewelfareoftheotherconsumer.,Pareto-Optimality,TheallocationisPareto-optimalsincetheonlywayoneconsumerswelfarecanbeincreasedistodecreasethewelfareoftheotherconsumer.,TheMarginalRatesofSubstitutionAreEqual.,Pareto-Optimality,WhereareallofthePareto-optimalallocationsoftheendowment?

Pareto-Optimality,OA,OB,Pareto-Optimality,OA,OB,AlltheallocationsmarkedbyaarePareto-optimal.,Pareto-Optimality,Thecontractcurve（契约线）isthesetofallPareto-optimalallocations.,Pareto-Optimality,OA,OB,AlltheallocationsmarkedbyaarePareto-optimal.,Thecontractcurve,Pareto-Optimality,Buttowhichofthemanyallocationsonthecontractcurvewillconsumerstrade?

Thatdependsuponhowtradeisconducted.Inperfectlycompetitivemarkets?

Byone-on-onebargaining?

TheCore（核心）,OA,OB,ThesetofPareto-improvingreallocations,TheCore,OA,OB,TheCore,OA,OB,Pareto-optimaltradesblockedbyB,Pareto-optimaltradesblockedbyA,TheCore,OA,OB,Pareto-optimaltradesnotblockedbyAorBarethecore.,TheCore,ThecoreisthesetofallPareto-optimalallocationsthatarewelfare-improvingforbothconsumersrelativetotheirownendowments.Rationaltradeshouldachieveacoreallocation.,TheCore,Butwhichcoreallocation?

Again,thatdependsuponthemannerinwhichtradeisconducted.,TradeinCompetitiveMarkets,Considertradeinperfectlycompetitivemarkets.Eachconsumerisaprice-takertryingtomaximizeherownutilitygivenp1,p2andherownendowment.Thatis,.,TradeinCompetitiveMarkets,OA,ForconsumerA.,TradeinCompetitiveMarkets,Sogivenp1andp2,consumerAsnetdemandsforcommodities1and2are,and,TradeinCompetitiveMarkets,And,similarly,forconsumerB,TradeinCompetitiveMarkets,ForconsumerB.,OB,TradeinCompetitiveMarkets,Sogivenp1andp2,consumerBsnetdemandsforcommodities1and2are,and,TradeinCompetitiveMarkets,Ageneralequilibriumoccurswhenpricesp1andp2causeboththemarketsforcommodities1and2toclear;i.e.,and,TradeinCompetitiveMarkets,OA,OB,TradeinCompetitiveMarkets,OA,OB,CanthisPOallocationbeachieved?

TradeinCompetitiveMarkets,OA,OB,BudgetconstraintforconsumerA,TradeinCompetitiveMarkets,OA,OB,BudgetconstraintforconsumerA,TradeinCompetitiveMarkets,OA,OB,BudgetconstraintforconsumerB,TradeinCompetitiveMarkets,OA,OB,BudgetconstraintforconsumerB,TradeinCompetitiveMarkets,OA,OB,But,TradeinCompetitiveMarkets,OA,OB,and,TradeinCompetitiveMarkets,Soatthegivenpricesp1andp2thereisanexcesssupplyofcommodity1excessdemandforcommodity2.Neithermarketclearssothepricesp1andp2donotcauseageneralequilibrium.,TradeinCompetitiveMarkets,OA,OB,SothisPOallocationcannotbeachievedbycompetitivetrading.,TradeinCompetitiveMarkets,OA,OB,WhichPOallocationscanbeachievedbycompetitivetrading?

TradeinCompetitiveMarkets,Sincethereisanexcessdemandforcommodity2,p2willrise.Sincethereisanexcesssupplyofcommodity1,p1willfall.Theslopeofthebudgetconstraintsis-p1/p2sothebudgetconstraintswillpivotabouttheendowmentpointandbecomelesssteep.,TradeinCompetitiveMarkets,OA,OB,WhichPOallocationscanbeachievedbycompetitivetrading?

TradeinCompetitiveMarkets,OA,OB,WhichPOallocationscanbeachievedbycompetitivetrading?

TradeinCompetitiveMarkets,OA,OB,WhichPOallocationscanbeachievedbycompetitivetrading?

TradeinCompetitiveMarkets,OA,OB,BudgetconstraintforconsumerA,TradeinCompetitiveMarkets,OA,OB,BudgetconstraintforconsumerA,TradeinCompetitiveMarkets,OA,OB,BudgetconstraintforconsumerB,TradeinCompetitiveMarkets,OA,OB,BudgetconstraintforconsumerB,TradeinCompetitiveMarkets,OA,OB,So,TradeinCompetitiveMarkets,OA,OB,and,TradeinCompetitiveMarkets,Atthenewpricesp1andp2bothmarketsclear;thereisageneralequilibrium.Question1:

Arepricesp1andp2determinedindependentlyatequilibrium?

Question2:

Doestheequilibriumexist?

WalrasLaw（瓦尔拉斯法则）,WalrasLawisanidentity;i.e.astatementthatistrueforanypositiveprices（p1,p2）,whethertheseareequilibriumpricesornot.,WalrasLaw,Everyconsumerspreferencesarewell-behavedso,foranypositiveprices（p1,p2）,eachconsumerspendsallofhisbudget.ForconsumerA:

ForconsumerB:

WalrasLaw,Summinggives,WalrasLaw,Rearranged,Thatis,.,WalrasLaw,Thissaysthatthesummedmarketvalueofexcessdemandsiszeroforanypositivepricesp1andp2-thisisWalrasLaw.,ImplicationsofWalrasLaw,SupposethemarketforcommodityAisinequilibrium;thatis,Then,implies,SooneimplicationofWalrasLawforatwo-commodityexchangeeconomyisthatifonemarketisinequilibriumthentheothermarketmustalsobeinequilibrium.Ingeneral,iftherearekmarkets,thenonlyk-1pricesaredeterminedatequilibrium.I.e.,thegeneralequilibriumdeterminesonlyrelativeprices.,ImplicationsofWalrasLaw,ImplicationsofWalrasLaw,Whatif,forsomepositivepricesp1andp2,thereisanexcessquantitysuppliedofcommodity1?

Thatis,Then,implies,ImplicationsofWalrasLaw,SoasecondimplicationofWalrasLawforatwo-commodityexchangeeconomyisthatanexcesssupplyinonemarketimpliesanexcessdemandintheothermarket.,ExistenceofEquilibrium,Requirethattheaggregateexcessdemandfunctionsbeacontinuousfunction,whichinturnrequirethatEachindividualsdemandfunctionbecontinuous,orEachconsumerissmallrelativetothemarket.,TradeinCompetitiveMarkets,TradingincompetitivemarketsachievesaparticularPareto-optimalallocationoftheendowments.ThisisanexampleoftheFirstFundamentalTheoremofWelfareEconomics.,FirstFundamentalTheoremofWelfareEconomics,Giventhatconsumerspreferencesarewell-behaved,tradinginperfectlycompetitivemarketsimplementsaPareto-optimalallocationoftheeconomysendowment.,TheEquilibriumwithMonopoly,SeeFig.30.5intextbook.,TheEquilibriumwithMonopoly,Figure30.6inbook.,ImplicitAssumptions,Noconsumptionexternality（外部效应）AgentsbehavecompetitivelyEquilibriumexists,MarketSocialism:

TheDebate,Langevs.HayekSocialismwitheconomicplanningS