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,(,200052):(),,..,();;,.:;;;:F224:A:1007-9807(2003)03-0028-070()..,,,,[15].,,[68]..(),..Bonanno,[5].Ireland,[9].,Bonnano,().Stutton,Motta,,(),,,[1012]..,Motta[13]..:,,;,,;,6320036JOURNALOFMANAGEMENTSCIENCESINCHINAVol.6No.3Jun.,2003:2001-09-26;:2003-03-20.:(70172001).:(1973),,.,,.,.,,..,,,[14].,,,(),Cournot.1.(),,();,,,.,(),(),,,..,,,....,s.L,sL;H,sH,sHsL.,1,,[0,],1/,.,([15])U(,si,pi,Di)=si+siDi-pii0(1):pi,((0,1)),,.Di().,,.C(si,Di)=s2i/2,i=H,L.,(R&D).,0,.,.(1),92U/9Di9si=0,.,DisiDi=9U/9Di9U/9sisiDi=si+DisiDi.:1,s2i/2,i=H,L;2Cournot..,HL,L.[0,923:L),;[L,HL),;[HL,],.,:U(HL,sH,DH,pH)=U(HL,sL,DL,pL)U(L,sL,DL,pL)=0DH=-HL,DL=HL-L(2).(1)(2),:pH=sH-(1-)sHDH-sLDL(3)pL=sL-(1-)sLDL-sLDH(4)DH=(1-)sH-sL(1-)2sH-sL-(1-)pH-pL(1-)2sH-sL(5)DL=-sH(1-)2sH-sL+pH-(1-)pLsH/sL(1-)2sH-sL(6)HH(pH,pL)=pHDH-C(sH)(7)LL(pH,pL)=pLDL-C(sL)(8)(3)(4)(7)(8),(DH,DL):DH=12(1-)(-sLsHDL)DL=12(1-)(-DH)(9)D3H=2(1-)sH-sL4(1-)2sH-sLD3L=(1-2)sH4(1-)2sH-sL(10)p3H=(1-)sHD3H=(1-)sH2(1-)sH-sL4(1-)2sH-sLp3L=(1-)sLD3L=(1-)sL(1-2)sH4(1-)2sH-sL3H=(1-)sHD32H-s2H/23L=(1-)sLD32L-s2L/2(11),,(,).-2(1-)sH-sL-sL-2(1-)sL4(1-)2sHsL-s2L0,,1-12sLsH.1-12sLsH.,.(10)(11)(sH,sL)(1-)sHD32H+2(1-)sHD3H9D3H9sH-sH=0(12)(1-)sLD32L+2(1-)sLD3L9D3L9sL-sL=0(13)9D3H9sH=2(1-2)(1-)sL[4(1-)2sH-sL]29D3L9sL=(1-2)sH[4(1-)2sH-sL]2(14)(10)(14)(12)(13)(1-2)sH-sL4(1-)2sH-sL2+2(1-2)sH-sL4(1-)2sH-sL2(1-2)(1-)sL[4(1-)2sH-sL]2=1(1-)(1-2)sH4(1-)2sH-sL2+2[(1-2)sH]2[4(1-)2sH-sL]3=1(1-)sH,sL0320036,,=10,,,1.1=0=1/4sH25.194233.4442sL9.022324.80191sH/sL2.792436.96477DH4.508346.439457DL2.745832.373695DH+DL7.254178.813152sAV19.0728625.72981pH113.5841161.5219pL24.77378.5487H194.7025480.8558L27.323298.76285:sAV=(DHsH+DLsL)/(DH+DL):1,,,,.,.2,H;L;,,,,,.,.[0,1/2],(=0),,;.[16].2(),(),,,.,,,,:C(si,Di)=(s2i/2)qi(i=H,L)(15):qi.,,..Gal2or,Mussa&Rosen,[6,7]..MottaGal2orGal2or(),Motta[13]..(3)(4)(15)(7),(8)(,qi=Di),(DH,DL):133:DH=14(1-)(2-sH-2sLsHDL)DL=14(1-)(2-sL-2DH)(DH,DL)Nash:D3H=sL[(sL-2)-2(1-)s2H+4(1-)sH]2[4(1-)2sH-sL]D3L=sH[sH+2(-(1-)sL)-2]2[4(1-)2sH-sL](16)p3H=sH[-sH(sL-4(1-)2)+(1-)sL(sL-2)+2(1-)2s2H]2[4(1-)2sH-sL]p3L=sL[s2L-(1-)s2H+2(1-)((1-)sL+(2-1))]2[4(1-)2sH-sL],,(,).-2(1-)sH-sL-sL-2(1-)sL4(1-)2sHsL-s2L0,,1-12sLsH.,1-12sLsH.H=(1-)sH[sL(sL-2)-2(1-)s2H-4(1-)2sH]4[4(1-)2sH-sL]2L=(1-)sLs2H[sH+2(-(1-)sL)-2]24[4(1-)2sH-sL]2,.(sH,sL):9(1-)sH[sL(sL-2)-2(1-)s2H-4(1-)2sH]4[4(1-)2sH-sL]2/9sH(17)9(1-)sLs2H[sH+2(-(1-)sL)-2]24[4(1-)2sH-sL]2/9sL(18)(17),(18).,.,(2).=0,=10,,=1/4,=10()2(,=0,=10(17)(18),,,sHsL,,).2=0=1/4sH7.38107.2932sL5.58585.9605sH/sL1.3213863731.223588625DH2.18562.6475DL2.44332.9149DH+DL4.62895.5624sAV6.4334288366.594816707pH43.370841.0766pL31.452230.7941H35.256438.3385L34.956637.9823:sAV=(DHsH+DLsL)/(DH+DL):32,,,,(2320036);().,,,,,,..1.,,.4,,.,.,().,,(3),,().,,.31212,:1)(sAV=(DHsH+DLsL)/(DH+DL)),.,.2)(=0),(sHsL)();(=1/4),.,,,.3)(DHDLDH+DL),.,,,,,,;.4,Cournot,.,.,,,..,,..333::[1]ShakedA,SuttonJ.Relaxingpricecompetitionthroughproductdifferentiation[J].ReviewofEconomicStudies,1982,49:314[2]ShakedA,SuttonJ.Naturaloligopolies[J].Econometrica,1983,51:14691483[3]ShakedA,SuttonJ.NaturalOligopoliesandInternationalTrade[M].InKierzkowskiHed.MonopolisticCompetitionandInterna2tionalTrade,Clarendon:OxfordPress,1984.231239[4]ShakedA,SuttonJ.Productdifferentiationandindustrialstructure[J].JournalofIndustrialEconomics,1987,36:131146[5]BonannoG.VerticaldifferentiationwithCournotcompetition[J].EconomicNotes,1986,15:6891[6]MussaM,RosenS.Monopolyandproductquality[J].JournalofEconomicTheory,1978,18:301317[7]Gal2OrE.Qualityandquantitycompetition[J].BellJournalofEconomics,1983,14:590600[8]ChampsaurP,RochetJ2C.Multiproductduopollists[J].Econometrica,1989,57:533557[9]IrelandN.ProductDifferentiationandNon-priceCompetition[M].Oxford:BasilBlackwellPress,1987.7174[10]SuttonJ.SunkCostsandMarketStructure[M].TheMITPress,1991.7176[11]MottaM.Sunkcostsandtradeliberalization[J].EconomicJournal,1992a,102:578587[12]MottaM.CooperativeR&Dandverticalproductdifferentiation[J].InternationalJournalofIndustrialOrganization,1992b,10:643661[13]MottaM.Endogenousqualitychoice:Pricevs.quantitycompetition[J].TheJournalofIndustrialEconomics,1993,41:113133[14]KatzML,ShapiroC.Networkexternalities,competition,andcompatibility[J].AmericanEconomicReview,1985,5:424440[15]BakkeP,BoomA.Verticalproductdifferentiation,networkexternalities,andcompatibilitydecisions[J].InternationalJournalofIndustrialOrganization,2001,19:267284[16],.[J].,2001,10(2):107112ReturnofscaleandproductdifferentiationwithnetworkexternalityPANXiao2jun,CHENHong2minInstituteofSystemEngineering,ShanghaiJiaotongUniversity,Shanghai200052,ChinaAbstract:Inaverticalproductdifferentiationmodel,firmsfirstsimultaneouslychoosetheirqualities,andthenchooseoutput.Wediscussandcomparetheequilibriumdegreeofqualitydifferentiation,quantityandreturnundertheassumptionofincreasinganddecreasingreturnofscalewithnetworkexternality.Thestudyshowsthattheprod2uctqualityunderdecreasingreturnsislowerthanthatunderincreasingreturnswithoutnetworkexternality;butwithnetworkexternalitythequalityofhigh-qualityproductunde