管经-管理经济学课件

第12章：具有市场力企业的决策LearningObjectivesDefinemarketpoweranddescribemeasurementofmarketpowerExplainwhyentrybarriersarenecessaryforlongrunmarketpoweranddiscussmajortypesofentrybarriersFindtheprofit‐maximizingoutput,price,andinputusageforamonopolistandmonopolisticcompetitorEmployempiricallyestimatedorforecasteddemand,averagevariablecost,andmarginalcosttocalculateprofit‐maximizingoutputandpriceformonopolisticormonopolisticallycompetitivefirmsSelectproductionlevelsatmultipleplantstominimizethetotalcostofproducingagiventotaloutputforafirm垄断Monopoly市场只有一个企业生产和销售没有相近替代品的差异化产品或服务新企业被阻止进入市场TheBiggestContract

intheentirehistoryofGazpromThe30-yearcontractstipulatesthat38billioncubicmetersofRussiangaswillbeannuallysuppliedtoChinaTheAntitrustCaseAgainstMicrosoftSoftwarepioneer,monopolist,orboth?IsGoogleaMonopoly?

In2011,Microsoftfiledacomplaintwith

theEuropeanCommissionthatGoogle

wasusingitsdominantpositionasan

Internetsearchenginetocreatean

effectivemonopolybyexcludingcompetitors.Googlearguesthatitsdominantmarketshareisduetothehigherqualityofitssearchengine,notanyattemptsthecompanyhasmadetoreducetheaccessofothersearchenginestoonlinecontent.市场力MarketPower企业提高价格而不失去全部销售量的能力任何面临向下倾斜需求曲线的企业都具有一定的市场力使得企业能够定价高于平均成本并且获取经济利润

（如果需求和成本情况允许）市场界定市场界定：在一定的地理区域内，识别所有的竞争厂商和竞争产品及服务。一个市场由所有生产相似产品的厂商构成。一个正确定义的市场，必须能够包括所有消费者认同可以相互替代的产品和服务。可以通过价格上升的影响来界定相近替代品：如果对市场的定义十分狭隘，那么价格的上升会使厂商的销量和利润大幅下降，说明市场界定过小；扩大市场范围，直到利润上升为止。如可口可乐的市场（DrPepperin1986）市场力的度量市场力的程度与需求价格弹性反向相关企业需求越缺乏弹性，企业的市场力就越大企业产品越缺乏相应的替代品，需求价格弹性（绝对值）越小，企业的市场力越大当完全弹性需求（水平需求）时，企业没有市场力市场力的度量勒纳指数（Lernerindex）估计价格水平与完全竞争条件下价格的偏离范围

：市场力的度量勒纳指数完全竞争条件下等于零随着市场力水平的提高而增加也等于

–1/E，表明指数（市场力）与需求价格弹性反向相关需求价格弹性（绝对值）越小，指数越大，市场力水平也越高市场力的度量如果消费者认为两种产品是可以替代的，那么需求的交叉价格弹性

(EXY)

为正产品的交叉价格弹性越高，两种产品的替代性越强，生产这两种产品的公司拥有的市场力就越弱集中度的衡量（赫芬达尔-赫希曼指数）TheDepartmentofJusticeandtheFederalTradeCommissionMergerGuidelinesMEASUREOFCONCENTRATION(Herfindahl-HirschmanIndex,HHI)1firm,100%marketshare(amonopoly):HHI=1002=10,0002firms,eachwitha50%marketshare:HHI=502+502=5,0004firms,withmarketsharesof30%,30%,20%,and20%:

HHI=302+302+202+202=2,60010firms,eachwithmarketsharesof10%:HHI=10(102)=1,000合并标准MERGERSTANDARDS合并后的HHI指数低于1,000.该市场不是集中的,因此合并不会遭到挑战；合并后的HHI指数介于1,000和1,800之间.这些市场的集中度不高，如果合并使HHI指数的提高低于100，这一合并不会受到挑战；如果合并使HHI指数提高大于100，则可能受到挑战.合并后HHI指数高于1,800.这些市场是高度集中的。使HHI指数提高低于50的合并，不会受到挑战；提高幅度在50到100之间的合并可能受到挑战；提高幅度超过100的合并必然受到挑战.1992年兼并指南下的兼并安全港安全不安全不安全安全安全不安全安全安全安全兼并后的HHIHHI增长1800100010050市场力的决定因素新厂商进入市场，会增加替代品的数量，从而削弱目前企业的市场力只有当存在比较强的进入壁垒时，市场中的厂商才能拥有较高水平的市场力强进入壁垒阻碍了新厂商的进入，从而保证了市场现存厂商的利润常见的进入壁垒政府设置的壁垒特许权或执照（电力、自来水、出租车等）专利和版权等自然垄断NaturalMonopoly（或者，规模经济Economiesofscale）在与产品需求相关的产量范围内，如果厂商的长期平均成本曲线是呈下降趋势的，那么会产生很强的进入壁垒沉没成本的进入壁垒Withanaturalmonopoly,theaveragetotalcostcurve

isstillfallingwhenitcrosses

thedemandcurve(pointA).Ifonlyonefirmisproducing

electricpowerinthemarket,anditproduceswherethe

averagecostcurve

intersectsthedemandcurve,averagetotalcostwillequal

$0.04perkilowatt-hourof

electricityproduced.Ifthemarketisdivided

betweentwofirms,eachproducing15billion

kilowatt-hours,theaveragecostofproducingelectricityrisesto$0.06perkilowatt-hour(pointB).Inthiscase,ifonefirmexpandsproduction,itcanmovedowntheaveragetotalcostcurve,loweritsprice,anddrivetheotherfirmoutofbusiness.NaturalmonopolyAsituationinwhicheconomiesofscalearesolargethatonefirmcansupplytheentiremarketataloweraveragetotalcostthancantwoormorefirms.常见的进入壁垒品牌效应Brandloyalties消费者对现有企业的忠诚度，使那些新进入市场的企业很难发现足够的买者，因而无法进入Realemon浓缩柠檬汁要素壁垒Inputbarriers一个企业控制了某一生产过程的关键投入要素美国铝业（Alcoa），或者资本、渠道等iOSAdiamondisforeverDeBeerspromotedthesentimentalvalueofdiamondsasawaytomaintainitspositioninthediamondmarket.TheEndoftheChristmasPlantMonopolyFormanyyears,thePaulEckeRanchinEncinitas,

Californiahadamonopolyonpoinsettias,whose

strikingredandgreencolorsthatblossominthe

wintermakethemidealforChristmasdecorating.Afterdiscoveringanewtechniqueforgrowingthe

wildflowerthatwaskeptsecretfordecades,the

Eckefamilywasabletomaintainamonopolyonits

commercialproductionwithoutacquiringapatent,untilauniversityresearcherdiscoveredthe

techniqueandpublisheditinanacademicjournal.Asaresult,manynewfirmsquicklyenteredthe

industryandthepriceofpoinsettiasplummeted.常见的进入壁垒网络外延Networkexternalities近20年计算机技术、互联网、新软件发展迅猛信息产品特点：无成本复制、快速扩散、不变质某种产品或服务的效用会随着使用人数的增加而增加，该产品或服务在消费中存在网络效应例子：微信，京东，大众点评网，标准，信用卡，DVD与碟片，苹果硬件、系统与软件，维护等一旦企业建立了巨大的消费者网络，新企业就难以进入市场，首先建立用户基础的企业具有先入优势POSITIVENETWORKEXTERNALITYinwhichaconsumerwishestopossessagoodinpartbecauseothersdoBandwagonEffect攀比效应Withapositivenetworkexternality,thequantityofagoodthatanindividualdemandsgrowsinresponsetothegrowthofpurchasesbyotherindividuals.Here,asthepriceoftheproductfallsfrom$30to$20,thebandwagoneffectcausesthedemandforthegoodtoshifttotheright,fromD40toD80.NEGATIVENETWORKEXTERNALITYinwhichaconsumerwishestoownanexclusiveoruniquegood.SnobEffect虚荣效应Thesnobeffectisanegativenetworkexternalityinwhichthequantityofagoodthatanindividualdemandsfallsinresponsetothegrowthofpurchasesbyotherindividuals.Here,asthepricefallsfrom$30,000to$15,000andmorepeoplebuythegood,thesnobeffectcausesthedemandforthegoodtoshifttotheleft,fromD2toD6.Althoughnotfirsttomarket,Bicultimatelywasmoresuccessfulthanthefirmthatpioneeredballpointpens.(vs.Reynolds)IsBeingtheFirstFirmintheMarketaKeytoSuccess?Thefirmsthatwerefirsttointroduceaproductultimatelylostouttoerswhodidabetterjobofprovidingconsumerswithproductsthatweremorereliable,lessexpensive,moreconvenient,orotherwiseprovidedgreatervalue.iPodHPLaserJetP&GPampersIE常见的进入壁垒消费者锁定Consumerlock-in如果潜在的进入者认为昂贵的转换成本使现有消费者不会转向其它品牌时，他们就被阻止进入了转换成本：安装或入会费；寻找可能替代品及其价格的成本；学习如何使用新的或者不同产品或服务的成本。高转换成本可能是自然形成的，也可能是企业战略性创造的例子：从Office到WPS?从Nikon到Canon？垄断厂商面临的需求和边际收益市场需求曲线就是垄断企业的需求曲线垄断者想要售出更多的产品，就必须降低价格（统一定价时）除了第一件产品，其余每件产品出售带来的边际收益都低于其价格当MR

为正值(负值)，需求具有弹性(缺乏弹性)垄断厂商面临的需求和边际收益垄断下的短期利润最大化(图12.3)垄断下的短期利润最大化如果部分需求曲线对应的价格水平高于平均变动成本，垄断厂商在短期内会进行生产通过MR=MC时的产出量，可以达到利润最大化，或亏损最小化垄断下的短期损失最小化(图12.4)垄断下的短期利润最大化若P>ATC,企业获利若ATC>P>AVC,企业产生亏损，但短期内仍继续生产若在任何产出水平需求曲线都低于AVC,企业会停止生产，以使亏损的部分只是固定成本不同于完全竞争市场，这里AVC不是最小值AVC处于下降阶段MaximizingProfit

P(Q)=24-Q

C(Q)=Q2+12

MonopolyExampleInversedemandfunction:Canbeusedtofindthemarginalrevenuefunction:

QuadraticSRcostfunction:Canbeusedtofindthemarginalcostfunction:

Profit-maximizingoutputisobtainedbyproducingQ*:SolvingthisexpressionrevealsQ*=6Theinversedemandfunctionindicatesthatpeoplearewillingtopayp=$18for6unitsofoutput.AppleintroduceditsiPodin2001DataMarginalcost=$200Fixedcost=$736millionDemandfunction:P=600-25Q(inmillion)Questions:Whatwereitsprofitmaximizingpriceandquantity,profit,andLernerIndex,priceelasticity?AnswerAC=200+736/QMR=600-50QQ=8million;P=$400Profit=(P-AC)Q=[400-(200+736/8)]*8=$864millionLernerIndex=[P-MC]/P=[400-200]/400=1/2PriceElasticity=-1/LI=-2Graph垄断下的长期利润最大化(图12.5)垄断下的长期利润最大化垄断厂商通过选择一个能够使MR=LMC的产出水平只要

PLAC，企业就实现了利润最大化如果

P<LAC，企业就退出市场垄断厂商将调整企业规模达到最优水平在利润最大化对应的产出水平上，短期平均成本曲线正好与长期成本曲线相切SHIFTSINDEMANDShiftingthedemandcurveshowsthatamonopolisticmarkethasnosupplycurve—i.e.,thereisnoone-to-onerelationshipbetweenpriceandquantityproduced.In(a),thedemandcurveD1shiftstonewdemandcurveD2.ButthenewmarginalrevenuecurveMR2intersectsmarginalcostatthesamepointastheoldmarginalrevenuecurveMR1.Theprofit-maximizingoutputthereforeremainsthesame,althoughpricefallsfromP1toP2.In(b),thenewmarginalrevenuecurveMR2intersectsmarginalcostatahigheroutputlevelQ2.Butbecausedemandisnowmoreelastic,priceremainsthesame.利润最大化决策的一般原则企业应该生产还是关门？对应某一产量水平，只要市场价格超过平均可变成本，就要生产：P>=AVC，否则关门如果生产，应该生产多少，价格为多少？为了保证利润最大化，在边际收益等于边际成本（MR=MC）点上决定产量，并以此产量按需求曲线决定价格ReplyfromProf.Christopher利润最大化产量与价格决策的实施Step1:估计需求函数广义需求函数估计（运用第七章的统计技术）用预测的外生变量的未来值代入估计的需求函数，得到利润最大化产量与价格决策的实施Step2:求需求函数的反函数解出P利润最大化产量与价格决策的实施Step3:求边际收益当需求函数表示为

P=A+BQ，边际收益函数写为利润最大化产量与价格决策的实施Step4:估计AVC&SMC运用第十章的统计技术AVC=a+bQ+cQ2SMC=a+2bQ+3cQ2Step5:找出

MR=SMC的产出水平令边际收益等于边际成本，解出

Q*两个解中大的一个就是利润最大化的产出量Step6:找出最优价格把

Q*

代入反需求函数，得P*=A+BQ*只有PAVC时，所得出的

Q*&P*

才是最优的利润最大化产量与价格决策的实施利润最大化产量与价格决策的实施Step7:检验关门法则把

Q*

代入到估计的AVC方程若

P*

AVC*，产出为Q*

且售价为

P*

若P*

<AVC*，短期关门AVC*=a+bQ*+cQ*2利润最大化产量与价格决策的实施Step8:计算利润或亏损Profit=TR–TC

=PxQ*-AVCxQ*-TFC=(P–AVC)Q*-TFC若P<AVC，垄断企业关门并且利润为-TFCAztecElectronics的利润最大化因为拥有专利，Aztec拥有市场力销售高级无线立体声耳机，市场需求：固定成本$270,000，平均变动成本：

AVC=28–0.005Q+0.000001Q2预计2015年：M=$45,000,PR=$800企业的利润最大化决策是什么？AztecElectronics的利润最大化估计需求和边际收益函数AztecElectronics的利润最大化求反需求函数AztecElectronics的利润最大化确定边际收益函数P=100–0.002QMR=100–0.004QAztecElectronics的需求和边际收益AztecElectronics的利润最大化估计平均变动成本函数和边际成本函数estimatedAVCequation:AVC=28–0.005Q+0.000001Q2Then,SMC=28–(2x0.005)Q+(3x0.000001)Q2=28–0.01Q+0.000003Q2AztecElectronics的利润最大化确定产量令

MR=MC

并求解

Q*100–0.004Q=28–0.01Q+0.000003Q20=(28–100)+(-0.01+0.004)Q+0.000003Q2=-72–0.006Q+0.000003Q2AztecElectronics的利润最大化确定产量用二次方程公式解出

Q*AztecElectronics的利润最大化确定价格把

Q*

代入到反需求函数P*=100–0.002(6,000)=$88AztecElectronics的利润最大化关门决策计算6,000单位时的

AVC:AVC*=28-0.005(6,000)+0.000001(6,000)2=$34BecauseP=$88>$34=ATC,AztecshouldproduceratherthanshutdownAztecElectronics的利润最大化计算总利润π

=TR–TVC–TFC=

(P*

xQ*)–(AVC*

xQ*)–TFC=($88x6,000)–($34x6,000)-$270,000=$528,000-$204,000-$270,000=$54,000若人均收入下降，导致企业需求下降：P=80-0.002Q，成本不变，企业如何决策？AztecElectronics的利润最大化ELASTICITYOFDEMANDANDPRICEMARKUPTheRuleofThumbforPricingThemarkup(P−MC)/Pisequaltominustheinverseoftheelasticityofdemand.Ifthefirm’sdemandiselastic,asin(a),themarkupissmallandthefirmhaslittlemonopolypower.Theoppositeistrueifdemandisrelativelyinelastic,asin(b).

MARKUPPRICING:SUPERMARKETSTODESIGNERJEANSAlthoughtheelasticityofmarketdemandforfoodis

small(about−1),nosinglesupermarketcanraiseits

pricesverymuchwithoutlosingcustomerstoother

stores.Theelasticityofdemandforanyonesupermarketis

oftenaslargeas−10.WefindP=MC/(1−0.1)=

MC/(0.9)=(1.11)MC.Themanagerofatypicalsupermarketshouldsetpricesabout11percentabovemarginalcost.Smallconveniencestorestypicallychargehigherpricesbecauseitscustomersaregenerallylesspricesensitive.Becausetheelasticityofdemandforaconveniencestoreisabout−5,themarkupequationimpliesthatitspricesshouldbeabout25percentabovemarginalcost.Withdesignerjeans,demandelasticitiesintherangeof−2to−3aretypical.Thismeansthatpriceshouldbe50to100percenthigherthanmarginalcost.垄断的福利代价与竞争企业相比，垄断者收取高于边际成本的价格。从消费者的立场看，高价格使垄断不合意

对企业拥有者来说，高价格使垄断非常合意垄断会降低经济效率吗?完全竞争与垄断的比较ComparingMonopolyandPerfectCompetitionEquilibriuminaperfectlycompetitivemarketresultsinthegreatestamountofeconomicsurplus,ortotalbenefittosociety,fromtheproductionofagoodorservice.Amonopolywillproducelessandchargeahigherpricethanwouldaperfectlycompetitiveindustryproducingthesamegood.WhatHappensIfaPerfectlyCompetitiveIndustryesaMonopoly?Inpanel(a),themarketfortabletcomputersisperfectlycompetitive,andpriceandquantityaredeterminedbytheintersectionofthedemandandsupplycurves.Inpanel(b),theperfectlycompetitivetabletcomputerindustryesamonopoly.Asaresult:1.Theindustrysupplycurveesthemonopolist’smarginalcostcurve.2.Themonopolistreducesoutputtowheremarginalrevenueequalsmarginalcost,QM.3.ThemonopolistraisesthepricefromPCtoPM.Amonopolycharges

ahigherprice,PM,andproducesa

smallerquantity,QM,thanaperfectlycompetitiveindustry,whichchargespricePCandproducesQC.Thehigherpricereducesconsumersurplusby

theareaequaltotherectangleAandthetriangleB.Someofthereductioninconsumersurplusiscapturedbythemonopolyasproducersurplus,andsomeesdeadweightloss,whichistheareaequal

totrianglesBandC.TheInefficiencyofMonopoly市场势力与技术进步MarketPowerandTechnologicalChangeFirmsareoftenforcedtorelyontheirprofitstofinancetheresearchanddevelopmentneededfornewproducts,butsmallerfirmsdevelopanumberofnewproductsthemselvesaswell.Governmentpolicymakerscontinuetostrugglewiththeissueofwhether,onbalance,largefirmswithmarketpoweraregoodorbadfortheeconomy.AStaticViewofMonopoly:TheMarketforDrugsQuantity0CostsandRevenueDemandMarginalrevenuePriceduringpatentlifeMonopolyquantityPriceafterpatentexpiresMarginalcostCompetitivequantityADynamicViewofMonopoly:TheMarketforPCsMergers:TheTrade-offbetweenMarketPowerandEfficiencyTwofactorscancomplicateregulatinghorizontalmergers:The“market”thatfirmsareinisnotalwaysclear.Thereisthepossibilitythatthenewlymergedfirmmightbemoreefficientthanthemergingfirmswereindividually.Inpractice,thegovernmentdefinestherelevantmarketonthebasisofwhetherthereareclosesubstitutesfortheproductsbeingmadebythemergingfirms.Evenifamergedfirmismoreefficientandhaslowercosts,thatmaynotoffsettheincreasedmarketpowerofthefirmenoughtoincreaseconsumersurplusandeconomicefficiency.HorizontalmergerAmergerbetweenfirmsinthesameindustry.VerticalmergerAmergerbetweenfirmsatdifferentstagesofproduction

ofagood.Thefigureshowstheresultofallthefirmsinaperfectlycompetitiveindustrymergingtoformamonopoly.Ifcostsareunaffectedbythemerger,theresultis:PricerisesfromPCtoPM,quantityfallsfromQCtoQM,consumersurplusdeclines,andalossofeconomicefficiencyresults.If,however,themonopolyhaslowercoststhantheperfectlycompetitivefirms,asshownbythemarginalcostcurveshiftingtoMCafterthemerger,itispossiblethatthepricewillactuallydeclinefromPCtoPMergeandthatoutputwillincreasefromQCtoQMergefollowingthemerger.AMergerThatMakesConsumersBetterOffAlthoughthenewlymergedfirmhasagreatdealofmarketpower,becauseitismoreefficient,consumersarebetteroffandeconomicefficiencyisimproved.政府对垄断的干预法规管制公有制无所作为用反托拉斯法增强竞争反托拉斯法是一些旨在抑制垄断势力的法规反托拉斯法允许政府用不同的途径促进竞争阻止合并分解公司阻止企业从事减弱市场竞争的活动。管制Regulation政府可以管制垄断者的定价Governmentmayregulatethepricesthatthemonopolycharges.价格控制（增加产出/减少供给）Ratecontrol平均成本定价Average-costpricing边际成本定价Marginal-costpricingTHESOCIALCOSTSOFMONOPOLYPOWERIfleftalone,amonopolistproducesQmandchargesPm.WhenthegovernmentimposesapriceceilingofP1thefirm’saverageandmarginalrevenueareconstantandequaltoP1foroutputlevelsuptoQ1.Forlargeroutputlevels,theoriginalaverageandmarginalrevenuecurvesapply.Thenewmarginalrevenuecurveis,therefore,thedarkpurpleline,whichintersectsthemarginalcostcurveatQ1.PriceRegulationTHESOCIALCOSTSOFMONOPOLYPOWERWhenpriceisloweredtoPc,atthepointwheremarginalcostintersectsaveragerevenue,outputincreasestoitsmaximumQc.Thisistheoutputthatwouldbeproducedbyacompetitiveindustry.Loweringpricefurther,toP3reducesoutputtoQ3andcausesashortage,

Q’3−Q3.PriceRegulationRegulatingaNaturalMonopolyAnaturalmonopolythat

isnotsubjectto

governmentregulation

willchargeapriceequal

toPMandproduceQM.Ifgovernmentregulators

wanttoachieve

economicefficiency,theywillsettheregulated

priceequaltoPE,andthemonopolywill

produceQE.Unfortunately,PEis

belowaveragecost,andthemonopolywill

sufferaloss,shownbytheshadedrectangle.Becausethemonopolywillnotcontinuetoproduceinthelongrunifitsuffersaloss,governmentregulatorssetapriceequaltoaveragecost,whichisPRinthefigure.Theresultingproduction,QR,willbebelowtheefficientlevel.Localorstateregulatorycommissionsusuallysetthepricesfornaturalmonopolies.规制Regulation难以有效规制政府难以获得垄断企业的边际、平均成本线；定价不能低到垄断企业亏损（p>ac）；在确定价格下垄断企业会提供次品，以次充好Marginal-CostPricingforaNaturalMonopoly公有制PublicOwnership政府管制的不是由私人企业经营的自然垄断，而是自己经营自然垄断。

投票机制不如利润动机可靠。如美国公交政府制造竞争（招标）。无所作为DoingNothing如果市场失灵的程度远远小于政治失灵，政府就不再干预。Governmentcandonothingatallifthemarketfailureisdeemedsmallcomparedtotheimperfectionsofpublicpolicies.美国经济“市场失灵”的程度远小于根植于现实政治制度中经济政策不完善所引起的“政治失灵”垄断竞争MonopolisticCompetition垄断竞争的特征：企业数量多而规模相对较小；产品相似但又彼此有差别；企业在市场上的进入和退出不受限制。星巴克（Starbucks）

的兴衰星巴克：不再差异化？Starbucks:Nolongerdifferentenough?开始的繁荣1971年开出第一家店（西雅图）1993年在东海岸开店上十年繁荣，全球38个国家经营，共有17000家店激烈的竞争和不景气的经济2008年在美国关闭600家2009年在美国关闭300多家降价克服“$4咖啡之家”印象在垄断竞争的市场，长期维持利润非常困难！2011年恢复盈利垄断竞争与完全竞争、垄断的比较垄断竞争与完全竞争的差别：在垄断竞争条件下，企业生产有差异的产品；垄断竞争与垄断的差别：在垄断竞争条件下，企业可以自由进出市场。假设：单个企业的产出相对于整个市场的销售来说数量很小，所以单个企业的价格与产出决策不会为市场中其他企业所察觉，企业之间独立运作垄断竞争下的短期利润最大化(图12.7)垄断竞争下的长期均衡(图12.8)新企业进入侵蚀利润垄断竞争短期均衡等同于垄断没有进入退出限制导致了长期均衡当每个厂商的需求曲线与长期平均成本曲线LAC相切时在均衡产出水平下，P=LAC

且

MR=LMC长期均衡更像一种趋势Starbucks面临McDonald's竞争Theeffectofentryonprice,quantity,andprofitsatStarbucks.WhatHappenstoProfitsintheLongRun?垄断竞争厂商的处境类似于查尔斯·狄更斯在《圣诞颂》（ChristmasCarol）中描述的EbenezerScrooge遇到死神的情景。当看到自己死亡景象时，他问死神：那件事（死亡）的预兆是将来必然发生的，还是仅仅可能会发生的？利润终结的预兆萦绕在每个厂商所有者心中并挥之不去。TheShortRunandtheLongRunforaMonopolisticallyCompetitiveFirmRelationshipbetweenPrice

andAverageTotalCostProfitandLossElasticityofDemandCurveRelationshipbetweenPrice

andMarginalCostShortRunP>MCLongRunP>MCShortRunP>MCShortRunEconomicprofitShortRunLesselasticdemandcurveorP<ATCorEconomiclossLongRunP=MCLongRunZeroeconomicprofitLongRunMoreelasticdemandcurveAbercrombie&Fitch:CantheProductBeTooDifferentiated?DidAbercrombieandFitchnarrowitstargetmarkettoomuch?Afirmwhosestrategyofproductdifferentiationsucceedswillexperienceincreasesinsame-storesales.CanItBeProfitabletoBetheHigh-PriceSeller?Becausethegreaterdemandmorethanoffsetsthehighercosts,thehhgreggstoremakesalargerprofit.MidnightSnackFigure1:Productdifferentiationshiftingthedemand

curveforamonopolisticcompetitorFigure2:“Spreadingtheoverhead”垄断竞争与完全竞争的长期均衡比较Inpanel(b),amonopolisticallycompetitivefirmproducesatQMC,wherepriceisgreaterthanmarginalcost,andaveragetotalcostisnotataminimum.Asaresult,themonopolisticallycompetitivefirmisneitherallocativelyefficientnorproductivelyefficient.Themonopolisticallycompetitivefirmhasexcesscapacityequaltothedifferencebetweenitsprofit-maximizinglevelofoutputandtheproductivelyefficientlevelofoutput.垄断竞争与完全竞争的长期均衡比较定价高于其边际成本，没有配置效率；不在平均成本最低点上生产，没有生产效率；增加产量可以降低其平均成本。IsMonopolisticCompetitionInefficient?HowConsumersBenefitfromMonopolisticCompetitionConsumersbenefitfrombeingabletopurchaseaproductthatisdifferentiatedandmorecloselysuitedtotheirtastes.MarketingAlltheactivitiesnecessaryforafirmtosellaproducttoaconsumer.BrandmanagementTheactionsofafirmintendedtomaintainthedifferentiationofaproductovertime.AdvertisingIftheincreaseinrevenuethatresultsfromadvertisingisgreaterthantheincreaseincosts,thefirm’sprofitswillrise.DefendingaBrandNameAfirmcanapplyforatrademark,whichgrantslegalprotectionagainstotherfirmsusingitsproduct’sname.Legallyenforcingtrademarkscanbedifficult.U.S.firmsoftenfinditdifficulttoenforcetheirtrademarksinthecourtsofsomeforeigncountries,Product

Differentiation差异化战略：品牌与广告销售差异化产品的企业：通常花费其总收益的10-20%用于广告。总体上讲，企业大约用其收益的2%作广告。广告AdvertisementWhenfirmsselldifferentiatedproductsandchargepricesabovemarginalcost,eachfirmhasanincentivetoadvertiseinordertoattractmorebuyerstoitsparticularproduct.品牌管理BrandManagementBrandManagementTheactionsofafirmintendedtomaintainthedifferentiationofaproductovertime.Inmanymarkets,brandnameproductscoexistwithgenericones.Firmswithbrandnamesusuallyspendmoreonadvertising,chargehigherpricesfortheproducts.Aswithadvertising,thereisdisagreementabouttheeconomicsofbrandnames…

What’sYourOpinions？0TheCritiqueofBrandNamesCriticsofbrandnamesbelieve:Brandnamescauseconsumerstoperceivedifferencesthatdonotreallyexist.Consumers’willingnesstopaymoreforbrandnamesisirrational,fosteredbyadvertising.Eliminatinggovtprotectionoftrademarkswouldreduceinfluenceofbrandnames,

resultinlowerprices.0TheDefenseofBrandNamesDefendersofbrandnamesbelieve:Brandnamesprovideinformationaboutqualitytoconsumers.信息并不在广告的内容中，而仅仅在于广告的存在与其昂贵的价格中。Companieswithbrandnameshaveincentivetomaintainquality,toprotectthereputationoftheirbrandnames.0EFFECTSOFADVERTISINGTheDecisionWhethertoAdvertiseD（AR）andMRaredemandandmarginalrevenuewhenthefirmdoesn’tadvertise,andACandMCareaverageandmarginalcost.ThefirmproducesQ0andreceivesapriceP0.Itstotalprofitπ0isgivenbythegray-shadedrectangle.Ifthefirmadvertises,itsdemandandmarginalrevenuecurvesshifttotheright.Averagecostrises(toAC′)butmarginalcostremainsthesame.ThefirmnowproducesQ1(whereMR′=MC),andreceivesapriceP1.Itstotalprofit,π1,isnowlarger.HowMuchtoAdvertiseGiventhemaximizationproblem:Theprofit-maximizingo