melitz论文讲解

Melitz(2003),Outline,1.Summary,2.setupofthemodel,3.FirmEntryandExit,4.Closed-economyEqlm,6.Open-economyEqlm,7.ImpactofTrade,8.Conclusions,5.Overviewandassumptionoftheopeneconomymodel,Melitz(2003),Summary1.Themodelshowshowtheexposuretotradewillinduceonlythemoreproductivefirmstoentertheexportmarket(whilesomelessproductivefirmstocontinuetoproduceonlyforthedomesticmarket)andwillforcetheleastproductivefirmstoexit.2.Itthenshowshowfurtherincreasesintheexposuretotradeleadtoadditionalinter-firmreallocationstowardsmoreproductivefirms.3.Thepaperalsoshowshowtheaggregateindustryproductivitygrowthgeneratedbythereallocationscontributestoawelfaregain,thushighlightingabenefitfromtradethathasnotbeenexaminedtheoreticallybefore.,Summary,Thepaperdevelopsadynamicindustrymodelwithheterogeneousfirmstoanalyzetheintra-industryeffectsofintltrade.,Rigorousempiricalworkhasrecentlycorroboratedthisanecdotalevidence.BernardandJensen(1999a)(fortheU.S.)Aw,Chung,andRoberts(2000)(forTaiwan),Clerides,Lack,andTybout(1998)(forColombia,Mexico,andMorocco)allfindevidencethatmoreproductivefirmsself-selectintoexportmarkets.Aw,Chung,andRoberts(2000)alsofindevidencesuggestingthatexposuretotradeforcestheleastproductivefirmstoexit.Pavcnik(2002)directlylooksatthecontributionofmarketsharereallocationstosectoralproductivitygrowthfollowingtradeliberalizationinChile.Shefindsthatthesereallocationssignificantlycontributetoproductivitygrowthinthetradablesectors.Inarelatedstudy,BernardandJensen(1999b)findthatwithinsectormarketsharereallocationstowardsmoreproductiveexportingplantsaccountsfor20%ofU.S.manufacturingproductivitygrowth.,Melitz(2003),ThepaperadaptsHopenhayns(1992a)dynamicindustrymodeltomonopolisticcompetitioninaequilibriumsetting.general(Hopenhayns(1992a,1992b)worktoexplaintheendogenousselectionofheterogeneousfirmsinanindustry;Hopenhaynonlyconsiderscompetitivefirms)thepaperprovidesanextensionofKrugmans(1980)trademodelthatincorporatesfirmlevelproductivitydifferences.,Summary,Melitz(2003),5,Melitz(2003),2.1DemandPreferences:CESutilitycontinuumofgoodsmassofavailablegoods,elasticityofsubstitutionbetweentwogoodsDefine:aggregategood:aggregateprice:Optimalconsumptionandexpenditure:,2.setupofthemodel,6,Melitz(2003),2.2SupplyThereexistsacontinuumoffirms,eachchoosingtoproduceadifferentvariety,withonefactorlabor.Productiontechnology:fixedcost:productivity:FOCoffirmsprofitmaximizationproblemimplies:=1:commonwageratewhichimpliesconstantmarkup:andfirmprofit:Revenueandprofitasfunctionsofaggregatevariables:,Equations(3)-(6):moreproductivefirms(higher)willbebigger(largeroutputandrevenues),chargealowerprice,andearnhigherprofits.,7,Melitz(2003),2.3AggregationEqlm:(1)amassoffirms(andgoods):(2)adistributionofproductivity:Aggregate/Averageproductivity:Otheraggregatevariables:Otheraveragevariables:,8,Melitz(2003),3.FirmEntryandExitToentertheindustry,firmsmustinvestafixedentrycost:Afterentry,firmsdrawtheirproductivityfromacommondistn,withacumulativedistributionandsupportover.Ifproductivityislow,thefirmeither(1)exitimmediately,or(2)produce,butfacesaprobofofabadshockineachperiodthatforcesittoexit.Newentrants(includingunsuccessfulones)willhave,onaverage,lowerproductivityandahigherprobofexitthanincumbents.Firmsvaluefunction:Cutoffproductivityofproducingfirms:If,thefirmwillexitimmediately.,9,Melitz(2003),3.FirmEntryandExitEqlmproductivitydistnistheconditionaldistnofonwhereistheex-anteprobofsuccessfulentry.Aggregateproductivityisafunctionofthecutoffproductivity:Averagerevenueandprofit,10,Melitz(2003),3.FirmEntryandExit3.1Zerocutoffprofit(ZCP)condition(afterentry):3.2Freeentry(FE)condition(beforeentry)-presentvalueoftheaverageprofitflow:-netvalueofentry:,11,Melitz(2003),4.Closed-economyEqlm,12,Melitz(2003),4.Closed-economyEqlmInastationaryeqlm:-numberoffirmsisstable:(ismassofnewentrants)-labormarketclears:laborforproduction:laborforentrycost:Thus-massofproducingfirms:4.1analysisoftheequilibrium-welfareperworker:(13)and(14):L(economysize)M(varieties)W(welfare),13,Melitz(2003),-theexportmarketentrydecisionoccursafterthefirmgainsknowledgeofitsproductivity,-wherebyunitsofagoodmustbeshippedinorderfor1unittoarriveatdestination,-identicalcountries:,inordertoensurefactorpriceequalizationacrosscountries,-n+12countries),allcountriessharethesamewage,-Exporttoanyforeigncountryrequiresafixedcost:,14,Melitz(2003),6.Open-economyEqlmTimingofevents:Entrydecision(basedon)productivity()isrevealedproductiondecision(basedon)andexportdecision(basedon)Pricesfortwomarkets:Revenuefortwomarkets:Combinedrevenue:,15,Melitz(2003),6.Open-economyEqlmProfitsfortwomarkets:whereisamortizedper-periodfixedexportcost.Combinedprofit:Firmsvaluefunction:-cutoffproductivityforentry:-cutoffproductivityforexporting:bydefinition:Conditionforpartitionoffirms:combinewithand(16)toget:-if,novariablecostcaninducethepartition.-if,itwillinducepartitionevenifnovariablecost(=1).,16,Melitz(2003),6.Open-economyEqlmEqlmdistnoffirms:-Eqlmdistnofproductivitylevelforincumbentfirms:-Ex-anteprobofsuccessfulentry:-Ex-anteprobthatonesuccessfulfirmexports:Somenotations:-:eqlmmassofincumbentfirms.-:massofexportingfirms.-:totalmassofvarietiesavailableinanycountry.,17,Melitz(2003),6.Open-economyEqlm6.2Aggregation:-Averageproductivity:-Aggregatepriceindex,expenditure,andwelfareperworker.-Overallaverageofrevenueandprofit:,18,Melitz(2003),6.Open-economyEqlm6.3Eqlmconditions:-Zerocutoffprofit(ZCP)condition:-Freeentry(FE)condition:-presentvalueofaverageprofit:-netvalueofentry:-freeentrycondition:,19,Melitz(2003),6.Open-economyEqlm6.4Determinationofeqlm-ZCP+FE-Stabilitycondition:-Aggregaterevenueandlabor:-Thesepindowneqlmmassofincumbentfirms:massofvarietyavailable:andtheirpriceindex:,20,7.ImpactofTradeCompareautarky(closed-economy)andopen-economyeqlm.denoteautarkycutoffandaverageproductivity:FEcondition:identicalinboththeclosedandopeneconomy.ZCPcondition:compare(12)and(20)ZCPcurveshiftsup.Eqlmcutoffproductivity:-domesticmarketselectionprocess:theleastproductivefirmswithproductivitybetweenexittheindustry.-exportmarketselectionprocess:onlythefirmwithproductivityaboveentertheexportmarket.-bothprocessesreallocatemarketsharestowardsmoreproductivefirms,andcontributetoanaggregateproductivitygain.,21,7.ImpactofTradeEqlmnumberoffirms/varieties-numberofsurvivingdomesticfirms:(13)and(21):-numberofvarietiesavailable:7.1Reallocationofmarketsharesandprofits:-marketshares:compare:-Afirmwhodoesnotexportlosesmarketshare.-Afirmwhoexportsgainsmarketshare.-profits:onlypartofmoreproductivefirmswhoexportgainfromtrade.,22,Melitz(2003),ImpactofTradeDalwinnianevolution:marketshareprofits-mostefficientfirms:-lessefficientfirms:-evenlessefficientfirms:-leastefficientfirm:00,23,Melitz(2003),ImpactofTrade,24,Melitz(2003),7.ImpactofTradeWhydoestradeforcetheleastproductivefirmstoexit?Twopotentialchannels:-Productmarketcompetition:firmsfaceanincreasingnumberofcompetitors,whichare,moreproductivethandomesticfirms.-Thischannelisnotoperativehere:monopolisticcompetitionunderCESpreferenceimpliespriceelasticityofdemand()doesnotrespondtochangesinthenumberorpricesofcompetingvarieties.-ThischannelisoperativeinMelitzandOttaviano(2008).-Labormarketcompetition:opentotradecausesnewprofitopportunities;butonlymoreproductivefirmsexport,andmoreprospectivefirmsenter;increaseoflabordemandofth