经济学原理-曼昆第七版第四讲讲义：Supply-and-Demand

经济学原理-曼昆第七版第四讲讲义：Supply-and-Demand第一页，共59页。QuestionsIfyouaremakingrealestateinvestmentdecisions,howwouldyoupredicttheeffectofthepolicychanges?WhataretherealfactordrivingtheresidentialhousingpriceinChina?Whatarethelong-runperspectivesofChineserealestatemarkets?2第二页，共59页。TheMarketMechanismAMarketisamechanismthroughwhichbuyersandsellersinteracttodeterminepricesandexchangegoods,services,andassetsGeographicalarea;Timeperiod;Good/servicebeingtradedThe“indivisiblehand”NosingleindividualororganizationorgovernmentisresponsibleforsolvingtheeconomicproblemsinamarketeconomyOursociety,despiteofitsfragility(surprise!),functionswellformostofthetimeinaspontaneousmannerToknowhowmarkethelptosolvetheimportantquestionsandtobefamiliarwiththefollowingeconomicconcepts,weneedtostudythedemandandsupplymodel(D-Smodel)Price;marketequilibrium;efficiency3第三页，共59页。MarketsandCompetitionSupplyanddemandWordseconomistsusemostoftenTheforcesthatmakemarketeconomiesworkRefertothebehaviorofpeopleastheyinteractwithoneanotherincompetitivemarkets4第四页，共59页。MarketsandCompetitionMarketAgroupofbuyersandsellersofaparticulargoodorserviceBuyersasagroupDeterminethedemandfortheproductSellersasagroupDeterminethesupplyoftheproduct5第五页，共59页。MarketsandCompetitionMarketstakemanyformsHighlyorganizedMarketsformanyagriculturalcommoditiesLessorganizedMarketforicecreaminaparticulartown6第六页，共59页。MarketsandCompetitionCompetitivemarketMarketinwhichtherearemanybuyersandmanysellersEachhasanegligibleimpactonmarketpricePriceandquantityaredeterminedbyallbuyersandsellersAstheyinteractinthemarketplace7第七页，共59页。MarketsandCompetitionPerfectlycompetitivemarketGoodsofferedforsaleareallexactlythesameBuyersandsellersaresonumerousNosinglebuyerorsellerhasanyinfluenceoverthemarketpricePricetakersAtthemarketpriceBuyerscanbuyalltheywantSellerscansellalltheywant8第八页，共59页。MarketsandCompetitionMonopolyTheonlysellerinthemarketSetsthepriceOthermarketsBetweenperfectcompetitionandmonopoly9第九页，共59页。DemandQuantitydemandedAmountofagoodthatbuyersarewillingandabletopurchaseLawofdemandOtherthingsequalWhenthepriceofagoodrises,thequantitydemandedofthegoodfallsWhenthepricefalls,thequantitydemandedrises10第十页，共59页。DemandDemandRelationshipbetweenthepriceofagoodandquantitydemandedDemandschedule:atableDemandcurve:agraphPriceontheverticalaxisQuantityonthehorizontalaxisIndividualdemandAnindividual’sdemandforaproduct11第十一页，共59页。Figure1Catherine’sDemandScheduleandDemandCurveDemandcurveThedemandscheduleisatablethatshowsthequantitydemandedateachprice.Thedemandcurve,whichgraphsthedemandschedule,illustrateshowthequantitydemandedofthegoodchangesasitspricevaries.Becausealowerpriceincreasesthequantitydemanded,thedemandcurveslopesdownward.PriceofIce-CreamConeQuantityofConesDemanded$0.000.501.001.502.002.503.0012cones10864200121011912345678QuantityofIce-CreamCones$3.002.502.001.501.000.50PriceofIce-CreamCones1.Adecreaseinprice...2....increasesquantityofconesdemanded.12第十二页，共59页。DemandMarketdemandSumofallindividualdemandsforagoodorserviceMarketdemandcurveSumtheindividualdemandcurveshorizontallyTotalquantitydemandedofagoodvariesAsthepriceofthegoodvariesOtherthingsconstant13第十三页，共59页。Figure2MarketDemandastheSumofIndividualDemandsThequantitydemandedinamarketisthesumofthequantitiesdemandedbyallthebuyersateachprice.Thus,themarketdemandcurveisfoundbyaddinghorizontallytheindividualdemandcurves.Atapriceof$2.00,Catherinedemands4ice-creamcones,andNicholasdemands3ice-creamcones.Thequantitydemandedinthemarketatthispriceis7cones.14第十四页，共59页。Figure2MarketDemandastheSumofIndividualDemandsDCatherine0121011912345678QuantityofIce-CreamCones$3.002.502.001.501.000.50PriceofIce-CreamConesCatherine’sdemandDNicholas01234567QuantityofIce-CreamCones$3.002.502.001.501.000.50PriceofIce-CreamConesNicholas’sdemand+=DMarket018246810121416QuantityofIce-CreamCones$3.002.502.001.501.000.50PriceofIce-CreamConesMarketdemand15第十五页，共59页。DemandShiftsinthedemandcurveIncreaseindemandAnychangethatincreasesthequantitydemandedateverypriceDemandcurveshiftsrightDecreaseindemandAnychangethatdecreasesthequantitydemandedateverypriceDemandcurveshiftsleft16第十六页，共59页。Figure3ShiftsintheDemandCurvePriceofIce-CreamConesQuantityofIce-CreamCones0Demandcurve,D1Demandcurve,D3Demandcurve,D2IncreaseinDemandDecreaseinDemandAnychangethatraisesthequantitythatbuyerswishtopurchaseatanygivenpriceshiftsthedemandcurvetotheright.Anychangethatlowersthequantitythatbuyerswishtopurchaseatanygivenpriceshiftsthedemandcurvetotheleft.17第十七页，共59页。DemandVariablesthatcanshiftthedemandcurveIncomePricesofrelatedgoodsTastesExpectationsNumberofbuyers18第十八页，共59页。DemandIncomeNormalgoodOtherthingsconstantAnincreaseinincomeleadstoanincreaseindemandInferiorgoodOtherthingsconstantAnincreaseinincomeleadstoadecreaseindemand19第十九页，共59页。DemandPricesofrelatedgoodsSubstitutes,twogoodsAnincreaseinthepriceofoneLeadstoanincreaseinthedemandfortheotherComplements,twogoodsAnincreaseinthepriceofoneLeadstoadecreaseinthedemandfortheother20第二十页，共59页。DemandTastesChangeintastes:changesthedemandExpectationsaboutthefutureExpectanincreaseinincomeIncreaseincurrentdemandExpecthigherpricesIncreaseincurrentdemandNumberofbuyers,increasesMarketdemandincreases21第二十一页，共59页。Table1VariablesThatInfluenceBuyersThistableliststhevariablesthataffecthowmuchconsumerschoosetobuyofanygood.Noticethespecialrolethatthepriceofthegoodplays:Achangeinthegood’spricerepresentsamovementalongthedemandcurve,whereasachangeinoneoftheothervariablesshiftsthedemandcurve.22第二十二页，共59页。TwowaystoreducethequantityofsmokingdemandedShiftthedemandcurveforcigarettesandothertobaccoproductsTrytoraisethepriceofcigarettes23“Whatisthebestwaytostopthis?”第二十三页，共59页。TwowaystoreducethequantityofsmokingdemandedShiftthedemandcurveforcigarettesandothertobaccoproductsPublicserviceannouncementsMandatoryhealthwarningsoncigarettepackagesProhibitionofcigaretteadvertisingontelevisionIfsuccessfulShiftdemandcurvetotheleft24第二十四页，共59页。TwowaystoreducethequantityofsmokingdemandedTrytoraisethepriceofcigarettesTaxthemanufacturer:higherpriceMovementalongdemandcurve10%↑

inprice→4%↓insmokingTeenagers:10%↑

inprice→12%↓insmokingDemandforcigarettesvs.demandformarijuanaAppeartobecomplements25第二十五页，共59页。Figure4ShiftsintheDemandCurveversusMovementsalongtheDemandCurvePriceofCigarettes,perPackNumberofCigarettesSmokedperDay0D1D2Apolicytodiscouragesmokingshiftsthedemandcurvetotheleft1020$2.00BA(a)AShiftintheDemandCurveIfwarningsoncigarettepackagesconvincesmokerstosmokeless,thedemandcurveforcigarettesshiftstotheleft.Inpanel(a),thedemandcurveshiftsfromD1toD2.Atapriceof$2.00perpack,thequantitydemandedfallsfrom20to10cigarettesperday,asreflectedbytheshiftfrompointAtopointB.Bycontrast,ifataxraisesthepriceofcigarettes,thedemandcurvedoesnotshift.Instead,weobserveamovementtoadifferentpointonthedemandcurve.Inpanel(b),whenthepricerisesfrom$2.00to$4.00,thequantitydemandedfallsfrom20to12cigarettesperday,asreflectedbythemovementfrompointAtopointC.PriceofCigarettes,perPackNumberofCigarettesSmokedperDay0D1Ataxthatraisesthepriceofcigarettesresultsinamovementalongthedemandcurve12202.00CA(b)AMovementalongtheDemandCurve$4.0026第二十六页，共59页。DemandFunctionTheDemandFunctiondescribestherelationshipbetweentheamountofagoodorservicethatconsumersarewillingtopurchaseQ=a-bP,a>0,b>0LawofDemand：-b<0InverseDemandFunction：P=a/b-1/bQ27第二十七页，共59页。SupplyQuantitysuppliedAmountofagoodSellersarewillingandabletosellLawofsupplyOtherthingsequalWhenthepriceofagoodrises,thequantitysuppliedofthegoodalsorisesWhenthepricefalls,thequantitysuppliedfallsaswell28第二十八页，共59页。SupplySupplyRelationshipbetweenthepriceofagoodandthequantitysuppliedSupplyschedule:atableSupplycurve:agraphPriceontheverticalaxisQuantityonthehorizontalaxisIndividualsupplyAseller’sindividualsupply29第二十九页，共59页。Figure5Ben’sSupplyScheduleandSupplyCurvePriceofIce-creamConeQuantityOfConesSupplied$0.000.501.001.502.002.503.000cones012345SupplycurveThesupplyscheduleisatablethatshowsthequantitysuppliedateachprice.Thissupplycurve,whichgraphsthesupplyschedule,illustrateshowthequantitysuppliedofthegoodchangesasitspricevaries.Becauseahigherpriceincreasesthequantitysupplied,thesupplycurveslopesupward.0121011912345678QuantityofIce-CreamCones$3.002.502.001.501.000.50PriceofIce-CreamCones1.Anincreaseinprice...2....increasesquantityofconessupplied.30第三十页，共59页。SupplyMarketsupplySumofthesuppliesofallsellersforagoodorserviceMarketsupplycurveSumofindividualsupplycurveshorizontallyTotalquantitysuppliedofagoodvariesAsthepriceofthegoodvariesAllotherfactorsthataffecthowmuchsupplierswanttosellareholdconstant31第三十一页，共59页。Figure6MarketSupplyastheSumofIndividualSuppliesThequantitysuppliedinamarketisthesumofthequantitiessuppliedbyallthesellersateachprice.Thus,themarketsupplycurveisfoundbyaddinghorizontallytheindividualsupplycurves.Atapriceof$2.00,Bensupplies3ice-creamcones,andJerrysupplies4ice-creamcones.Thequantitysuppliedinthemarketatthispriceis7cones.32第三十二页，共59页。Figure6MarketSupplyastheSumofIndividualSuppliesSBen01234567QuantityofIce-CreamCones$3.002.502.001.501.000.50PriceofIce-CreamConesBen’ssupplySJerry01234567QuantityofIce-CreamCones$3.002.502.001.501.000.50PriceofIce-CreamConesJerry’ssupply+=SMarket018246810121416QuantityofIce-CreamCones$3.002.502.001.501.000.50PriceofIce-CreamConesMarketsupply33第三十三页，共59页。SupplyShiftsinsupplyIncreaseinsupplyAnychangethatincreasesthequantitysuppliedateverypriceSupplycurveshiftsrightDecreaseinsupplyAnychangethatdecreasesthequantitysuppliedateverypriceSupplycurveshiftsleft34第三十四页，共59页。Exhibit7ShiftsintheSupplyCurvePriceofIce-CreamConesQuantityofIce-CreamCones0Supplycurve,S1Supplycurve,S3Supplycurve,S2IncreaseinSupplyDecreaseInsupplyAnychangethatraisesthequantitythatsellerswishtoproduceatanygivenpriceshiftsthesupplycurvetotheright.Anychangethatlowersthequantitythatsellerswishtoproduceatanygivenpriceshiftsthesupplycurvetotheleft.35第三十五页，共59页。SupplyVariablesthatcanshiftthesupplycurveInputpricesTechnologyExpectationsaboutfutureNumberofsellers36第三十六页，共59页。SupplyInputpricesSupplyisnegativelyrelatedtopricesofinputsHigherinputprices:decreaseinsupplyTechnologyAdvanceintechnology:increaseinsupply37第三十七页，共59页。SupplyExpectationsaboutfutureAffectcurrentsupplyExpectedhigherpricesDecreaseincurrentsupplyNumberofsellers,increasesMarketsupplyincreases38第三十八页，共59页。Table2VariablesThatInfluenceSellersThistableliststhevariablesthataffecthowmuchproducerschoosetosellofanygood.Noticethespecialrolethatthepriceofthegoodplays:Achangeinthegood’spricerepresentsamovementalongthesupplycurve,whereasachangeinoneoftheothervariablesshiftsthesupplycurve.39第三十九页，共59页。SupplyFunctionThesupplyfunctiondescribestherelationshipbetweentheamountofagoodorservicethatfirmsarewillingtosellandtherelevantenvironmentalvariablesQ=c+dP,c>0,d>040第四十页，共59页。SupplyandDemandTogetherEquilibriumVariousforcesareinbalanceAsituationinwhichmarketpricehasreachedthelevelwhereQuantitysupplied=quantitydemandedSupplyanddemandcurvesintersect41第四十一页，共59页。SupplyandDemandTogetherEquilibriumpriceBalancesquantitysuppliedandquantitydemandedMarket-clearingpriceEquilibriumquantityQuantitysuppliedandquantitydemandedattheequilibriumprice42第四十二页，共59页。Figure8TheEquilibriumofSupplyandDemandSupply0121011912345678QuantityofIce-CreamCones$3.002.502.001.501.000.50PriceofIce-CreamConesEquilibriumDemandEquilibriumpriceEquilibriumquantityTheequilibriumisfoundwherethesupplyanddemandcurvesintersect.Attheequilibriumprice,thequantitysuppliedequalsthequantitydemanded.Heretheequilibriumpriceis$2.00:Atthisprice,7ice-creamconesaresupplied,and7ice-creamconesaredemanded.43第四十三页，共59页。SupplyandDemandTogetherSurplusQuantitysupplied>quantitydemandedExcesssupplyDownwardpressureonpriceMovementsalongthedemandandsupplycurvesIncreaseinquantitydemandedDecreaseinquantitysupplied44第四十四页，共59页。SupplyandDemandTogetherShortageQuantitydemanded>quantitysuppliedExcessdemandUpwardpressureonpriceMovementsalongthedemandandsupplycurvesDecreaseinquantitydemandedIncreaseinquantitysupplied45第四十五页，共59页。Figure9MarketsNotinEquilibriumPriceofIce-CreamConesQuantityofIce-CreamCones0Demand7$2.50(a)ExcessSupplyInpanel(a),thereisasurplus.Becausethemarketpriceof$2.50isabovetheequilibriumprice,thequantitysupplied(10cones)exceedsthequantitydemanded(4cones).Supplierstrytoincreasesalesbycuttingthepriceofacone,andthismovesthepricetowarditsequilibriumlevel.Inpanel(b),thereisashortage.Becausethemarketpriceof$1.50isbelowtheequilibriumprice,thequantitydemanded(10cones)exceedsthequantitysupplied(4cones).Withtoomanybuyerschasingtoofewgoods,supplierscantakeadvantageoftheshortagebyraisingtheprice.Hence,inbothcases,thepriceadjustmentmovesthemarkettowardtheequilibriumofsupplyanddemand(b)Excessdemand2.00SupplySurplus4Quantitydemanded10QuantitysuppliedPriceofIce-CreamConesQuantityofIce-CreamCones0Demand71.50$2.00SupplyShortage4Quantitysupplied10Quantitydemanded46第四十六页，共59页。SupplyandDemandTogetherLawofsupplyanddemandThepriceofanygoodadjustsTobringthequantitysuppliedandthequantitydemandedforthatgoodintobalanceInmostmarketsSurplusesandshortagesaretemporary47第四十七页，共59页。SupplyandDemandTogetherThreestepstoanalyzingchangesinequilibriumDecidewhethertheeventshiftsthesupplycurve,thedemandcurve,or,insomecases,bothcurvesDecidewhetherthecurveshiftstotherightortotheleftUsethesupply-and-demanddiagramComparetheinitialandthenewequilibriumEffectsonequilibriumpriceandquantity48第四十八页，共59页。Table3ThreeStepsforAnalyzingChangesinEquilibriumDecidewhethertheeventshiftsthesupplyordemandcurve(orperhapsboth).2.Decideinwhichdirectionthecurveshifts.3.Usethesupply-anddemanddiagramtoseehowtheshiftchangestheequilibriumpriceandquantity.49第四十九页，共59页。SupplyandDemandTogetherAchangeinmarketequilibriumduetoashiftindemandOnesummer,veryhotweatherEffectonthemarketforicecream?Hotweather:shiftsthedemandcurve(tastes)DemandcurveshiftstotherightHigherequilibriumprice;higherequilibriumquantity50第五十页，共59页。Figure10HowanincreaseindemandaffectstheequilibriumSupplyNewequilibriumD2Aneventthatraisesquantitydemandedatanygivenpriceshiftsthedemandcurvetotheright.Theequilibriumpriceandtheequilibriumquantitybothrise.Hereanabnormallyhotsummercausesbuyerstodemandmoreicecream.ThedemandcurveshiftsfromD1toD2,whichcausestheequilibriumpricetorisefrom$2.00to$2.50andtheequilibriumquantitytorisefrom7to10cones.PriceofIce-CreamConesQuantityofIce-CreamCones07$2.502.0010D1Initialequilibrium1.Hotweatherincreasesthedemandforicecream...2.…resultinginahigherprice...3.…andahigherquantitysold.51第五十一页，共59页。SupplyandDemandTogetherShiftsvs.movementsalongcurvesShiftinthesupplycurveChangeinsupplyMovementalongafixedsupplycurveChangeinthequantitysuppliedShiftinthedemandcurveChangeindemandMovementalongafixeddemandcurveChangeinthequantitydemanded52第五十二页，共59页。SupplyandDemandTogetherAchangeinmarketequilibriumduetoashiftinsupplyOnesummer,ahurricanedestroyspartofthesugarcanecrop:higherpriceofsugarEffectonthemarketforicecream?Changeinpriceofsugar:supplycurveSupplycurve:shiftstotheleftHigherequilibriumprice;lowerequilibriumquantity53第五十三页，共59页。Figure11HowaDecreaseinSupplyAffectstheEquilibriumS1NewequilibriumS2Aneventthatreducesquantitysuppliedatanygivenpriceshiftsthesupplycurvetotheleft.Theequilibriumpricerises,andtheequilibriumquantityfalls.Hereanincreaseinthepriceofsugar(aninput)causessellerstosupplylessicecream.ThesupplycurveshiftsfromS1toS2,whichcausestheequilibriumpriceof