经济学原理 曼昆第七版第四讲讲义：Supply and Demand

1,.,Chapter4SupplyandDemandFall2017,2,.,Questions,Ifyouaremakingrealestateinvestmentdecisions,howwouldyoupredicttheeffectofthepolicychanges?WhataretherealfactordrivingtheresidentialhousingpriceinChina?Whatarethelong-runperspectivesofChineserealestatemarkets?,3,.,TheMarketMechanism,AMarketisamechanismthroughwhichbuyersandsellersinteracttodeterminepricesandexchangegoods,services,andassetsGeographicalarea;Timeperiod;Good/servicebeingtradedThe“indivisiblehand”NosingleindividualororganizationorgovernmentisresponsibleforsolvingtheeconomicproblemsinamarketeconomyOursociety,despiteofitsfragility(surprise!),functionswellformostofthetimeinaspontaneousmannerToknowhowmarkethelptosolvetheimportantquestionsandtobefamiliarwiththefollowingeconomicconcepts,weneedtostudythedemandandsupplymodel(D-Smodel)Price;marketequilibrium;efficiency,4,.,MarketsandCompetition,SupplyanddemandWordseconomistsusemostoftenTheforcesthatmakemarketeconomiesworkRefertothebehaviorofpeopleastheyinteractwithoneanotherincompetitivemarkets,5,.,MarketsandCompetition,MarketAgroupofbuyersandsellersofaparticulargoodorserviceBuyersasagroupDeterminethedemandfortheproductSellersasagroupDeterminethesupplyoftheproduct,6,.,MarketsandCompetition,MarketstakemanyformsHighlyorganizedMarketsformanyagriculturalcommoditiesLessorganizedMarketforicecreaminaparticulartown,7,.,MarketsandCompetition,CompetitivemarketMarketinwhichtherearemanybuyersandmanysellersEachhasanegligibleimpactonmarketpricePriceandquantityaredeterminedbyallbuyersandsellersAstheyinteractinthemarketplace,8,.,MarketsandCompetition,PerfectlycompetitivemarketGoodsofferedforsaleareallexactlythesameBuyersandsellersaresonumerousNosinglebuyerorsellerhasanyinfluenceoverthemarketpricePricetakersAtthemarketpriceBuyerscanbuyalltheywantSellerscansellalltheywant,9,.,MarketsandCompetition,MonopolyTheonlysellerinthemarketSetsthepriceOthermarketsBetweenperfectcompetitionandmonopoly,10,.,Demand,QuantitydemandedAmountofagoodthatbuyersarewillingandabletopurchaseLawofdemandOtherthingsequalWhenthepriceofagoodrises,thequantitydemandedofthegoodfallsWhenthepricefalls,thequantitydemandedrises,11,.,Demand,DemandRelationshipbetweenthepriceofagoodandquantitydemandedDemandschedule:atableDemandcurve:agraphPriceontheverticalaxisQuantityonthehorizontalaxisIndividualdemandAnindividualsdemandforaproduct,12,.,Figure1,CatherinesDemandScheduleandDemandCurve,Thedemandscheduleisatablethatshowsthequantitydemandedateachprice.Thedemandcurve,whichgraphsthedemandschedule,illustrateshowthequantitydemandedofthegoodchangesasitspricevaries.Becausealowerpriceincreasesthequantitydemanded,thedemandcurveslopesdownward.,13,.,Demand,MarketdemandSumofallindividualdemandsforagoodorserviceMarketdemandcurveSumtheindividualdemandcurveshorizontallyTotalquantitydemandedofagoodvariesAsthepriceofthegoodvariesOtherthingsconstant,14,.,Figure2,MarketDemandastheSumofIndividualDemands,Thequantitydemandedinamarketisthesumofthequantitiesdemandedbyallthebuyersateachprice.Thus,themarketdemandcurveisfoundbyaddinghorizontallytheindividualdemandcurves.Atapriceof$2.00,Catherinedemands4ice-creamcones,andNicholasdemands3ice-creamcones.Thequantitydemandedinthemarketatthispriceis7cones.,15,.,Figure2,MarketDemandastheSumofIndividualDemands,Catherinesdemand,Nicholassdemand,+,=,Marketdemand,16,.,Demand,ShiftsinthedemandcurveIncreaseindemandAnychangethatincreasesthequantitydemandedateverypriceDemandcurveshiftsrightDecreaseindemandAnychangethatdecreasesthequantitydemandedateverypriceDemandcurveshiftsleft,17,.,Figure3,ShiftsintheDemandCurve,Anychangethatraisesthequantitythatbuyerswishtopurchaseatanygivenpriceshiftsthedemandcurvetotheright.Anychangethatlowersthequantitythatbuyerswishtopurchaseatanygivenpriceshiftsthedemandcurvetotheleft.,18,.,Demand,VariablesthatcanshiftthedemandcurveIncomePricesofrelatedgoodsTastesExpectationsNumberofbuyers,19,.,Demand,IncomeNormalgoodOtherthingsconstantAnincreaseinincomeleadstoanincreaseindemandInferiorgoodOtherthingsconstantAnincreaseinincomeleadstoadecreaseindemand,20,.,Demand,PricesofrelatedgoodsSubstitutes,twogoodsAnincreaseinthepriceofoneLeadstoanincreaseinthedemandfortheotherComplements,twogoodsAnincreaseinthepriceofoneLeadstoadecreaseinthedemandfortheother,21,.,Demand,TastesChangeintastes:changesthedemandExpectationsaboutthefutureExpectanincreaseinincomeIncreaseincurrentdemandExpecthigherpricesIncreaseincurrentdemandNumberofbuyers,increasesMarketdemandincreases,22,.,Table1,VariablesThatInfluenceBuyers,Thistableliststhevariablesthataffecthowmuchconsumerschoosetobuyofanygood.Noticethespecialrolethatthepriceofthegoodplays:Achangeinthegoodspricerepresentsamovementalongthedemandcurve,whereasachangeinoneoftheothervariablesshiftsthedemandcurve.,23,.,Twowaystoreducethequantityofsmokingdemanded,ShiftthedemandcurveforcigarettesandothertobaccoproductsTrytoraisethepriceofcigarettes,“Whatisthebestwaytostopthis?”,24,.,Twowaystoreducethequantityofsmokingdemanded,ShiftthedemandcurveforcigarettesandothertobaccoproductsPublicserviceannouncementsMandatoryhealthwarningsoncigarettepackagesProhibitionofcigaretteadvertisingontelevisionIfsuccessfulShiftdemandcurvetotheleft,25,.,Twowaystoreducethequantityofsmokingdemanded,TrytoraisethepriceofcigarettesTaxthemanufacturer:higherpriceMovementalongdemandcurve10%inprice4%insmokingTeenagers:10%inprice12%insmokingDemandforcigarettesvs.demandformarijuanaAppeartobecomplements,26,.,Figure4,ShiftsintheDemandCurveversusMovementsalongtheDemandCurve,(a)AShiftintheDemandCurve,Ifwarningsoncigarettepackagesconvincesmokerstosmokeless,thedemandcurveforcigarettesshiftstotheleft.Inpanel(a),thedemandcurveshiftsfromD1toD2.Atapriceof$2.00perpack,thequantitydemandedfallsfrom20to10cigarettesperday,asreflectedbytheshiftfrompointAtopointB.Bycontrast,ifataxraisesthepriceofcigarettes,thedemandcurvedoesnotshift.Instead,weobserveamovementtoadifferentpointonthedemandcurve.Inpanel(b),whenthepricerisesfrom$2.00to$4.00,thequantitydemandedfallsfrom20to12cigarettesperday,asreflectedbythemovementfrompointAtopointC.,(b)AMovementalongtheDemandCurve,27,.,DemandFunction,TheDemandFunctiondescribestherelationshipbetweentheamountofagoodorservicethatconsumersarewillingtopurchaseQ=a-bP,a0,b0LawofDemand：-b0,d0,41,.,SupplyandDemandTogether,EquilibriumVariousforcesareinbalanceAsituationinwhichmarketpricehasreachedthelevelwhereQuantitysupplied=quantitydemandedSupplyanddemandcurvesintersect,42,.,SupplyandDemandTogether,EquilibriumpriceBalancesquantitysuppliedandquantitydemandedMarket-clearingpriceEquilibriumquantityQuantitysuppliedandquantitydemandedattheequilibriumprice,43,.,Figure8,TheEquilibriumofSupplyandDemand,Theequilibriumisfoundwherethesupplyanddemandcurvesintersect.Attheequilibriumprice,thequantitysuppliedequalsthequantitydemanded.Heretheequilibriumpriceis$2.00:Atthisprice,7ice-creamconesaresupplied,and7ice-creamconesaredemanded.,44,.,SupplyandDemandTogether,SurplusQuantitysuppliedquantitydemandedExcesssupplyDownwardpressureonpriceMovementsalongthedemandandsupplycurvesIncreaseinquantitydemandedDecreaseinquantitysupplied,45,.,SupplyandDemandTogether,ShortageQuantitydemandedquantitysuppliedExcessdemandUpwardpressureonpriceMovementsalongthedemandandsupplycurvesDecreaseinquantitydemandedIncreaseinquantitysupplied,46,.,Figure9,MarketsNotinEquilibrium,(a)ExcessSupply,Inpanel(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)Excessdemand,47,.,SupplyandDemandTogether,LawofsupplyanddemandThepriceofanygoodadjustsTobringthequantitysuppliedandthequantitydemandedforthatgoodintobalanceInmostmarketsSurplusesandshortagesaretemporary,48,.,SupplyandDemandTogether,ThreestepstoanalyzingchangesinequilibriumDecidewhethertheeventshiftsthesupplycurve,thedemandcurve,or,insomecases,bothcurvesDecidewhetherthecurveshiftstotherightortotheleftUsethesupply-and-demanddiagramComparetheinitialandthenewequilibriumEffectsonequilibriumpriceandquantity,49,.,Table3,ThreeStepsforAnalyzingChangesinEquilibrium,50,.,SupplyandDemandTogether,AchangeinmarketequilibriumduetoashiftindemandOnesummer,veryhotweatherEffectonthemarketforicecream?Hotweather:shiftsthedemandcurve(tastes)DemandcurveshiftstotherightHigherequilibriumprice;higherequilibriumquantity,51,.,Figure10,Howanincreaseindemandaffectstheequilibrium,Aneventthatraisesquantitydemandedatanygivenpriceshiftsthedemandcurvetotheright.Theequilibriumpriceandtheequilibriumquantitybothrise.Hereanabnormallyhotsummercausesbuyerstodemandmoreicecream.ThedemandcurveshiftsfromD1toD2,whichcausestheequilibriumpricetorisefrom$2.00to$2.50andtheequilibriumquantitytorisefrom7to10cones.,52,.,SupplyandDemandTogether,Shiftsvs.movementsalongcurvesShiftinthesupplycurveChangeinsupplyMovementalongafixedsupplycurveChangeinthequantitysuppliedShiftinthedemandcurveChangeindemandMovementalongafixeddemandcurveChangeinthequantitydemanded,53,.,SupplyandDemandTogether,AchangeinmarketequilibriumduetoashiftinsupplyOnesummer,ahurricanedestroyspartofthesugarcanecrop:higherpriceofsugarEffectonthemarketforicecream?Changeinpriceofsugar:supplycurveSupplycurve:shiftstotheleftHigherequilibriumprice;lowerequilibriumquantity,54,.,Figure11,HowaDecreaseinSupplyAffectstheEquilibrium,Aneventthatreducesquantitysuppliedatanygivenpriceshiftsthesupplycurvetotheleft.Theequilibriumpricerises,andtheequilibriumquantityfalls.Hereanincreaseinthepriceofsugar(aninput)causessellerstosupplylessicecream.ThesupplycurveshiftsfromS1toS2,whichcausestheequilibriumpriceoficecreamtorisefrom$2.00to$2.50andtheequilibriumquantitytofallfrom7to4cones.,55,.,SupplyandDemandTogether,ShiftsinbothsupplyanddemandOnesummer:hurricaneandheatwaveHeatwaveshiftsthedemandcurv