微观经济学现代观点讲义(清华大学 林徐)

ChapterOneTheMarketEconomicModeling‹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.01.01MarketDemandCurveforApartmentspQDModelingApartmentSupply‹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.DiscriminatoryMonopolisticMarketEquilibriumpQD,QS100p1=$5001DiscriminatoryMonopolisticMarketEquilibriumpQD,QS100p1=$500p2=$49012DiscriminatoryMonopolisticMarketEquilibriumpQD,QS100p1=$500p2=$49012p3=$4753DiscriminatoryMonopolisticMarketEq