6规模经济、不完全竞争和国际贸易

1YOUAREWELCOME!2InternationalEconomics国际经济学主讲：余道先[e-mail]3Chapter6EconomiesofScale，ImperfectCompetition,andInternationalTrade规模经济、不完全竞争和国际贸易4IntroductionEconomiesofScaleandInternationalTrade:AnOverviewEconomiesofScaleandMarketStructureTheTheoryofImperfectCompetitionMonopolisticCompetitionandTradeDumpingTheTheoryofExternalEconomiesExternalEconomiesandInternationalTradeSummaryPreview5IntroductionCountriesengageininternationaltradefortwobasicreasons:Countriestradebecausetheydiffereitherintheirresourcesorintechnology.Countriestradeinordertoachievescaleeconomiesorincreasingreturnsinproduction.6Introduction（cont.）TheRicardianandHeckscher-Ohlinmodelsalsorelyoncompetitiontopredictthatallincomefromproductionispaidtoownersoffactorsofproduction:no“excess”ormonopolyprofitsexist.Butwheneconomiesofscaleexist,largefirmsmaybemoreefficientthansmallfirms,andtheindustrymayconsistofamonopolyorafewlargefirms.Productionmaybeimperfectlycompetitiveinthesensethatexcessormonopolyprofitsarecapturedbylargefirms.7Introduction（cont.）Twomodelsofinternationaltradeinwhicheconomiesofscaleandimperfectcompetitionplayacrucialrole:Monopolisticcompetitionmodel（垄断竞争模型）Dumpingmodel（倾销模型）8EconomiesofScaleandInternationalTrade:AnOverviewModelsoftradebasedoncomparativeadvantage(e.g.Ricardianmodel)usedtheassumptionsofconstantreturnstoscaleandperfectcompetition:Increasingtheamountofallinputsusedintheproductionofanycommoditywillincreaseoutputofthatcommodityinthesameproportion（增加生产某商品所需的所有要素的投入会使该产品的产量同比例增加）.9EconomiesofScaleandInternationalTrade:AnOverviewInpractice,manyindustriesarecharacterizedbyeconomiesofscale(alsoreferredtoasincreasingreturns).Productionismostefficient,thelargerthescaleatwhichittakesplace（规模越大，生产效率越高）.10Underincreasingreturnstoscale:Outputgrowsproportionatelymorethantheincreaseinallinputs（产出的增长比例比要素投入增加的比例高）.Averagecosts(costsperunit)declinewiththesizeofthemarket（随着市场规模的扩张，平均成本（单位成本）降低）.EconomiesofScaleandInternationalTrade:AnOverview11EconomiesofScaleandInternationalTrade:AnOverviewTable6-1:RelationshipofInputtoOutputforaHypotheticalIndustry12EconomiesofScaleandMarketStructureEconomiesofscalecanbeeither:ExternalThecostperunitdependsonthesizeoftheindustrybutnotnecessarilyonthesizeofanyonefirm.（单位成本取决于产业规模，而并不一定由单一厂商的规模决定）Anindustrywilltypicallyconsistofmanysmallfirmsandbeperfectlycompetitive.（一个产业是由许多小厂商组成的，而且是完全竞争的）13EconomiesofScaleandMarketStructureInternalThecostperunitdependsonthesizeofanindividualfirmbutnotnecessarilyonthatoftheindustry.（单位成本是由单个厂商的规模决定的，而并不一定是由其所在产业的规模决定的）Themarketstructurewillbeimperfectlycompetitivewithlargefirmshavingacostadvantageoversmall.Bothtypesofscaleeconomiesareimportantcausesofinternationaltrade.（上述两种规模经济都是引起国际贸易的重要原因）14ImperfectcompetitionFirmsareawarethattheycaninfluencethepriceoftheirproduct.Theyknowthattheycansellmoreonlybyreducingtheirprice.Eachfirmviewsitselfasapricesetter,choosingthepriceofitsproduct,ratherthanapricetaker.Thesimplestimperfectlycompetitivemarketstructureisthatofapuremonopoly,amarketinwhichafirmfacesnocompetition.TheTheoryofImperfectCompetition15Monopoly:ABriefReviewMarginalrevenueTheextrarevenuethefirmgainsfromsellinganadditionalunitItscurve,MR,alwaysliesbelowthedemandcurve,D.Inordertosellanadditionalunitofoutputthefirmmustlowerthepriceofallunitssold(notjustthemarginalone).（为了多销售一单位产出，厂商必须降低所有(而不是最后一单位)出售产品的价格）TheTheoryofImperfectCompetition16TheTheoryofImperfectCompetitionFigure6-1:MonopolisticPricingandProductionDecisionsDCost,CandPrice,PQuantity,QMonopolyprofitsACPMQMMRMCAC17MarginalRevenueandPriceMarginalrevenueisalwayslessthantheprice.Assumethatthedemandcurvethefirmfacesisastraightline:Q=A–BxP(6-1)ThentheMRthatthefirmfacesisgivenby:MR=P–Q/B(6-2)TheTheoryofImperfectCompetition18TheTheoryofImperfectCompetitionAverageandMarginalCostsAverageCost(AC)istotalcostdividedbyoutput.MarginalCost(MC)istheamountitcoststhefirmtoproduceoneextraunit.Whenaveragecostsdeclineinoutput,marginalcostisalwayslessthanaveragecost.19Supposethecostsofafirm,C,taketheform:C=F+cxQ(6-3)Thisisalinearcostfunction.Thefixedcostinalinearcostfunctiongivesrisetoeconomiesofscale,becausethelargerthefirm’soutput,thelessisfixedcostperunit.Thefirm’saveragecostsisgivenby:AC=C/Q=F/Q+c(6-4)TheTheoryofImperfectCompetition20Figure6-2:AverageVersusMarginalCostTheTheoryofImperfectCompetitionAveragecostMarginalcost120345624681012141618202224CostperunitOutput21MonopolisticCompetition（垄断竞争）Monopolisticcompetitionisamodelofanimperfectlycompetitiveindustrywhichassumesthat：Eachfirmisassumedtobeabletodifferentiateitsproductfromitsrivals.（每个厂商均能生产与竞争对手有差异的产品）Eachfirmisassumedtotakethepriceschargedbyitsrivalsasgiven.（每个厂商把竞争对手的价格作为既定价格）TheTheoryofImperfectCompetition22Arethereanymonopolisticallycompetitiveindustriesintherealworld?（在现实中，是否存在垄断竞争行业？）Someindustriesmaybereasonableapproximations(e.g.,theautomobileindustryinEurope)Themainappealofthemonopolisticcompetitionmodelisnotitsrealism,butitssimplicity.TheTheoryofImperfectCompetition23AssumptionsoftheModelI