中级微观范里安课堂讲义-英文版(上)(上海交通大学,赵旭 朱保华)

ChapterOneTheMarketTheTheoryofEconomicsdoesnotfurnishabodyofsettledconclusionsimmediatelyapplicabletopolicy.Itisamethodratherthanadoctrine,anapparatusofthemind,atechniqueofthinkingwhichhelpsitspossessortodrawcorrectconclusions---JohnMaynardKeynesEconomicModelingWhatcauseswhatineconomicsystems?Atwhatlevelofdetailshallwemodelaneconomicphenomenon?Whichvariablesaredeterminedoutsidethemodel(exogenous)andwhicharetobedeterminedbythemodel(endogenous)?ModelingtheApartmentMarketHowareapartmentrentsdetermined?Suppose–apartmentsarecloseordistant,butotherwiseidentical–distantapartmentsrentsareexogenousandknown–manypotentialrentersandlandlordsModelingtheApartmentMarketWhowillrentcloseapartments?Atwhatprice?Willtheallocationofapartmentsbedesirableinanysense?Howcanweconstructaninsightfulmodeltoanswerthesequestions?EconomicModelingAssumptionsTwobasicpostulates:–RationalChoice:Eachpersontriestochoosethebestalternativeavailabletohimorher.–Equilibrium:Marketpriceadjustsuntilquantitydemandedequalsquantitysupplied.ModelingApartmentDemandDemand:Supposethemostanyonepersoniswillingtopaytorentacloseapartmentis$500/month.Thenp=$500QD=1.Supposethepricehastodropto$490beforea2ndpersonwouldrent.Thenp=$490QD=2.ModelingApartmentDemandTheloweristherentalratep,thelargeristhequantityofcloseapartmentsdemandedpQD.Thequantitydemandedvs.pricegraphisthemarketdemandcurveforcloseapartments.MarketDemandCurveforApartmentspQDModelingApartmentSupplySupply:Ittakestimetobuildmorecloseapartmentssointhisshort-runthequantityavailableisfixed(atsay100).MarketSupplyCurveforApartmentspQS100CompetitiveMarketEquilibrium“low”rentalpricequantitydemandedofcloseapartmentsexceedsquantityavailablepricewillrise.“high”rentalpricequantitydemandedlessthanquantityavailablepricewillfall.CompetitiveMarketEquilibriumQuantitydemanded=quantityavailablepricewillneitherrisenorfallsothemarketisatacompetitiveequilibrium.CompetitiveMarketEquilibriumpQD,QS100CompetitiveMarketEquilibriumpQD,QSpe100CompetitiveMarketEquilibriumpQD,QSpe100Peoplewillingtopaypeforcloseapartmentsgetcloseapartments.CompetitiveMarketEquilibriumpQD,QSpe100Peoplewillingtopaypeforcloseapartmentsgetcloseapartments.Peoplenotwillingtopaypeforcloseapartmentsgetdistantapartments.CompetitiveMarketEquilibriumQ:Whorentsthecloseapartments?A:Thosemostwillingtopay.Q:Whorentsthedistantapartments?A:Thoseleastwillingtopay.Sothecompetitivemarketallocationisby“willingness-to-pay”.ComparativeStaticsWhatisexogenousinthemodel?–priceofdistantapartments–quantityofcloseapartments–incomesofpotentialrenters.Whathappensiftheseexogenousvariableschange?ComparativeStaticsSupposethepriceofdistantapartmentrises.Demandforcloseapartmentsincreases(rightwardshift),causingahigherpriceforcloseapartments.MarketEquilibriumpQD,QSpe100MarketEquilibriumpQD,QSpe100HigherdemandMarketEquilibriumpQD,QSpe100Higherdemandcauseshighermarketprice;samequantitytraded.ComparativeStaticsSupposethereweremorecloseapartments.Supplyisgreater,sothepriceforcloseapartmentsfalls.MarketEquilibriumpQD,QSpe100MarketEquilibriumpQD,QS100HighersupplypeMarketEquilibriumpQD,QSpe100Highersupplycausesalowermarketpriceandalargerquantitytraded.ComparativeStaticsSupposepotentialrenters’incomesrise,increasingtheirwillingness-to-payforcloseapartments.Demandrises(upwardshift),causinghigherpriceforcloseapartments.MarketEquilibriumpQD,QSpe100MarketEquilibriumpQD,QSpe100Higherincomescausehigherwillingness-to-payMarketEquilibriumpQD,QSpe100Higherincomescausehigherwillingness-to-pay,highermarketprice,andthesamequantitytraded.TaxationPolicyAnalysisLocalgovernmenttaxesapartmentowners.Whathappensto–price–quantityofcloseapartmentsrented?Isanyofthetax“passed”torenters?TaxationPolicyAnalysisMarketsupplyisunaffected.Marketdemandisunaffected.Sothecompetitivemarketequilibriumisunaffectedbythetax.Priceandthequantityofcloseapartmentsrentedarenotchanged.Landlordspayallofthetax.ImperfectlyCompetitiveMarketsAmongstmanypossibilitiesare:–amonopolisticlandlord–aperfectlydiscriminatorymonopolisticlandlord–acompetitivemarketsubjecttorentcontrol.AMonopolisticLandlordWhenthelandlordsetsarentalpricepherentsD(p)apartments.Revenue=pD(p).Revenueislowifp0RevenueislowifpissohighthatD(p)0.Anintermediatevalueforpmaximizesrevenue.MonopolisticMarketEquilibriumpQDLowpriceLowprice,highquantitydemanded,lowrevenue.MonopolisticMarketEquilibriumpQDHighpriceHighprice,lowquantitydemanded,lowrevenue.MonopolisticMarketEquilibriumpQDMiddlepriceMiddleprice,mediumquantitydemanded,largerrevenue.MonopolisticMarketEquilibriumpQD,QSMiddlepriceMiddleprice,mediumquantitydemanded,largerrevenue.Monopolistdoesnotrentallthecloseapartments.100MonopolisticMarketEquilibriumpQD,QSMiddlepriceMiddleprice,mediumquantitydemanded,largerrevenue.Monopolistdoesnotrentallthecloseapartments.100Vacantcloseapartments.PerfectlyDiscriminatoryMonopolisticLandlordImaginethemonopolistkneweveryone’swillingness-to-pay.Charge$500tothemostwilling-to-pay,charge$490tothe2ndmostwilling-to-pay,etc.DiscriminatoryMo