经济学（微观）（英文版原书第7版）课件 第3章　价格来源：需求和供给的相互作用

EconomicsSeventhEditionChapter3WherePricesComeFrom:TheInteractionofDemandandSupplyCopyright©2019,2017,2015PearsonEducation,Inc.AllRightsReserved.ChapterOutline3.1

TheDemandSideoftheMarket3.2

TheSupplySideoftheMarket3.3

MarketEquilibrium:PuttingDemandandSupplyTogether3.4

TheEffectofDemandandSupplyShiftsonEquilibriumWhatDeterminesthePriceofPremiumBottledWater?Demand

forpremiumwaterHowmanybottlesdoconsumerswanttobuy?AffectedbypriceofthepremiumbottledwaterAffectedbyotherfactors,includingpricesofothergoodsSupplyofpremiumbottledwaterHowmanybottlesareproducerswillingtosell?AffectedbypriceofthepremiumbottledwaterAffectedbyotherfactors,includingpricesofothergoodsOurModelofaMarketToanalyzethemarketforpremiumbottledwater,weneedamodelofhowbuyersandsellersbehave.Themodelweuseinthischapterisaperfectlycompetitivemarket,amarketwith(1)manybuyersandsellers,(2)allfirmssellingidenticalproducts,and(3)nobarrierstonewfirmsenteringthemarket.Whiletheseassumptionsarequiterestrictive,themodelisstillusefulforanalyzingmanymarkets.3.1TheDemandSideoftheMarketListanddescribethevariablesthatinfluencedemand.Webeginouranalysisofwherepricescomefrombyinvestigatinghowbuyersbehave.Werefertothisasmarketdemand,thedemandbyalltheconsumersofagivengoodorservice.Figure3.1ADemandScheduleandaDemandCurve(1of3)Demandschedule:Atablethatshowstherelationshipbetweenthepriceofaproductandthequantityoftheproductdemanded.Demandcurve:Acurvethatshowstherelationshipbetweenthepriceofaproductandthequantityoftheproductdemanded.Figure3.1ADemandScheduleandaDemandCurve(2of3)Whendrawingthedemandcurve,weassumeceterisparibus.Ceterisparibus(“allelseequal”)condition:

Therequirementthatwhenanalyzingtherelationshipbetweentwovariables—suchaspriceandquantitydemanded—othervariablesmustbeheldconstant.Figure3.1ADemandScheduleandaDemandCurve(3of3)Quantitydemanded:Theamountofagoodorservicethataconsumeriswillingandabletopurchaseatagivenprice.Lawofdemand:Arulethatstatesthat,holdingeverythingelseconstant,whenthepriceofaproductfalls,thequantitydemandedoftheproductwillincrease,andwhenthepriceofaproductrises,thequantitydemandedoftheproductwilldecrease.WhatExplainstheLawofDemand?Whenthepriceofagoodfalls,twoeffectstakeplace:Consumerssubstitutetowardthegoodwhosepricehasfallen.Consumershavemorepurchasingpower,whichislikeanincreaseinincome.Wecallthesethesubstitutioneffectandtheincomeeffect:Substitutioneffect:Thechangeinthequantitydemandedofagoodthatresultsfromachangeinprice,makingthegoodmoreorlessexpensiverelativetoothergoodsthataresubstitutes.Incomeeffect:Thechangeinthequantitydemandedofagoodthatresultsfromtheeffectofachangeinthegood’spriceonaconsumers’purchasingpower.Figure3.2ShiftingtheDemandCurve(1of2)Achangeinsomethingotherthanpricethataffectsdemandcausestheentiredemandcurvetoshift.Ashifttotheright(D1toD2)isanincreaseindemand.Ashifttotheleft(D1toD3)isadecreaseindemand.Figure3.2ShiftingtheDemandCurve(2of2)Asthedemandcurveshifts,thequantitydemandedwillchange,evenifthepricedoesn’tchange.Thequantitydemandedchangesateverypossibleprice.WhatFactorsInfluenceMarketDemand?IncomeIncreaseinincomeincreasesdemandifproductisnormal,decreasesdemandifproductisinferior.PricesofrelatedgoodsIncreaseinpriceofrelatedgoodincreasesdemandifproductsaresubstitutes,decreasesdemandifproductsarecomplements.TastesPopulationanddemographicsExpectedfuturepricesWewilldiscusshoweachoftheseaffectsdemand.ChangesinIncomeofConsumersNormalgoods:Goodsforwhichthedemandincreasesasincomerisesanddecreasesasincomefalls.Examples: NewclothesRestaurantmealsVacationsInferiorgoods:Goodsforwhichthedemandincreasesasincomefallsanddecreasesasincomerises.Examples: Second-handclothesRamennoodlesEffectsofChangesinIncomeAnincreaseinincomewouldincreasethedemandfornewclothes,ceterisparibus.Howeverthesameincreaseinincomewouldlikelydecreasethedemandforsecond-handclothes.ChangesinthePriceofRelatedGoodsSubstitutes:Goodsandservicesthatcanbeusedforthesamepurpose.Examples: BigMacandWhopperFordF-150andDodgeRamJeansandKhakisComplements:Goodsandservicesthatareusedtogether.Examples: BigMacandMcDonald’sfriesHotdogsandhotdogbunsLeftshoesandrightshoesEffectsofChangesinthePriceofRelatedGoodsAnincreaseinthepriceofaBigMacwouldincreasethedemandforWhoppers.HoweverthesameincreaseinthepriceofaBigMacwoulddecreasethedemandforMcDonald’sfries.ApplytheConcept:AreThereEnoughComplementsforVirtualRealityHeadsets?VirtualrealityheadsetsarepotentialsuperiorsubstitutesforgameconsoleslikeSonyPlaystationorMicrosoftXbox.Butthoseconsolesalreadyhavemanycomplements:gamesproducedforthem.Fornow,salesofvirtualrealityheadsetsarelagging;onemainreasonisthelackofdesirablecomplements—games.ChangesinTastesTastesIfconsumers’tasteschange,theymaybuymoreorlessoftheproduct.Example:Ifconsumersbecomemoreconcernedabouteatinghealthily,theymightdecreasetheirdemandforfastfood.ChangesinPopulation/DemographicsDemographics:Thecharacteristicsofapopulationwithrespecttoage,race,andgender.Increasesinthenumberofpeoplebuyingsomethingwillincreasetheamountdemanded.Example:Anincreaseintheelderlypopulationincreasesthedemandformedicalcare.ChangesinExpectationsaboutFuturePricesConsumersdecidewhichproductstobuyandwhentobuythem.Futureproductsaresubstitutesforcurrentproducts. Anexpected

increase

inthepricetomorrowincreases

demand

today.Anexpected

decrease

inthepricetomorrowdecreases

demand

today.Example:Ifyoufoundoutthepriceofgasolinewouldgouptomorrow,youwouldincreaseyourdemandtoday.ApplytheConcept:Apple’sPolicyonProductSpeculationApplestronglydiscouragesitsemployeesfromspeculatingaboutwhenanewmodelwillappear.Why?SupposeacustomerlearnsthatanewiPadmodelwillbeavailablenextmonth.Thenewmodelisapotentialsubstituteforthecurrentmodel.Thepriceofthecurrentmodelwilllikelyfallnextmonth.Botheffectsdecreasecurrentdemand(badforApple!).ChangeinDemandvs.ChangeinQuantityDemandedAchangeinthepriceoftheproductbeingexaminedcausesamovementalongthedemandcurve.Thisisachangeinquantitydemanded.Anyotherchangeaffectingdemandcausestheentiredemandcurvetoshift.Thisisachangeindemand.ApplytheConcept:ForecastingtheDemandforPremiumBottledWaterToforecastfuturedemandforpremiumbottledwater,manufacturersneedtoanticipatehowdemandwillchange:Howwillincomeschange?Howwilltheavailabilityofsubstituteschange?Howwillconsumers’tasteschange?Howwillconsumerdemographicschange?3.2TheSupplySideoftheMarketListanddescribethevariablesthatinfluencesupply.Therearesomesimilarities,andsomeimportantdifferencesbetweenthedemandandsupplysidesofthemarket.Inthissectionweexaminethemarketsupply,i.e.thedecisionsof(generally)firmsabouthowmuchofaproducttoprovideatvariousprices. Figure3.4ASupplyScheduleandSupplyCurve(1of2)Supplyschedule:Atablethatshowstherelationshipbetweenthepriceofaproductandthequantityoftheproductsupplied.Supplycurve:Acurvethatshowstherelationshipbetweenthepriceofaproductandthequantityoftheproductsupplied.Figure3.4ASupplyScheduleandSupplyCurve(2of2)Quantitysupplied:Theamountofagoodorservicethatafirmiswillingandabletosupplyatagivenprice.Lawofsupply:Therulethat,holdingeverythingelseconstant,increasesinpricecauseincreasesinthequantitysupplied,anddecreasesinpricecausedecreasesinthequantitysupplied.Figure3.5ShiftingtheSupplyCurve(1of2)Achangeinsomethingotherthanpricethataffectssupplycausestheentiresupplycurvetoshift.Ashifttotheright(S1toS3)isanincreaseinsupply.Ashifttotheleft(S1toS2)isadecreaseinsupply.Figure3.5ShiftingtheSupplyCurve(2of2)Asthesupplycurveshifts,thequantitysuppliedwillchange,evenifthepricedoesn’tchange.Thequantitysuppliedchangesateverypossibleprice.WhatFactorsInfluenceMarketSupply?PricesofinputsTechnologicalchangePricesofsubstitutesinproductionNumberoffirmsinthemarketExpectedfuturepricesWewilldiscusshoweachoftheseaffectssupply.ChangeinPricesofInputsInputsarethingsusedintheproductionofagoodorservice.Forasmartwatch,inputsincludethecomputerprocessor,plastic,andlabor.Anincreaseinthepriceofaninputdecreasestheprofitabilityofsellingthegood,causingadecreaseinsupply.Adecreaseinthepriceofaninputincreasestheprofitabilityofsellingthegood,causinganincreaseinsupply.TechnologicalChangeAfirmmayexperienceapositiveornegativechangeinitsabilitytoproduceagivenlevelofoutputwithagivenquantityofinputs.Wecallthisatechnologicalchange.Examples:Anew,moreproductivevarietyofwheatwouldincreasethesupplyofwheat.Governmentalrestrictionsonlanduseforagriculturemightdecreasethesupplyofwheat.PricesofRelatedGoodsinProductionManyfirmscanproduceandsellalternativeproducts.Example:AnIllinoisfarmercanplantcornorsoybeans.Ifthepriceofsoybeansrises,hewillplant(supply)lesscorn.Sometimes,twoproductsarenecessarilyproducedtogether.Example:Cattleprovidebothbeefandleather.Anincreaseinthepriceofbeefencouragesmorecattlefarming,andhenceincreasethesupplyofleather.NumberofFirmsandExpectedFuturePricesMorefirmsinthemarketwillresultinmoreproductavailableatagivenprice(greatersupply).Fewerfirms→supplydecreases.Ifafirmanticipatesthatthepriceofitsproductwillbehigherinthefuture,itmightdecreaseitssupplytodayinordertoincreaseitinthefuture.ApplytheConcept:ReleaseTimingofCollateralDamageTheArnoldSchwarzeneggerfilmCollateralDamagewasoriginallyscheduledtobereleasedonOctober5,2001.Thefilmcontainedplotelementsaboutterroristattacks.Theproductioncompany(WarnerBros.)decidedthemoviewouldhavehigherdemandifitdidnotshowimmediatelyafter9/11,soitwasdelayeduntilFebruary2002.i.e.currentsupplyofthefilmdecreasedbecausethe(relative)expectedfuturepriceincreased.Figure3.6AChangeinSupplyversusaChangeinQuantitySuppliedAchangeinthepriceoftheproductbeingexaminedcausesamovementalongthesupplycurve.Thisisachangeinquantitysupplied.Anyotherchangeaffectingsupplycausestheentiresupplycurvetoshift.Thisisachangeinsupply.3.3MarketEquilibrium:PuttingDemandandSupplyTogetherUseagraphtoillustratemarketequilibrium.Marketequilibriumisasituationinwhichquantitydemandedequalsquantitysupplied.Recallthatmarketswithmanybuyersandsellersareperfectlycompetitivemarkets;amarketequilibriuminoneofthesemarketsiscalledacompetitivemarketequilibrium.Thereare~45firmssellingpremiumbottledwater;wewillassumethisisenoughtogeneratecompetitivebehaviorinthemarketforpremiumbottledwater.Figure3.7MarketEquilibriumAtapriceof$1.50,consumerswanttobuy5bottlesperday,andproducerswanttosell5millionbottlesperday.Wesaytheequilibriumpriceinthismarketis$1.50,andtheequilibriumquantityis5millionbottlesperday.Sincebuyersandsellerswanttotradethesamequantityatthepriceof$1.50,wedonotexpectthepricetochange.Figure3.8TheEffectofSurplusesandShortagesontheMarketPrice(1of2)Whatifthepricewere$2.00instead?Atapriceof$2.00,consumerswanttobuy4millionbottles,whileproducerswanttosell6million.Thisgivesasurplusof2millionbottles;asituationinwhichquantitysuppliedisgreaterthanquantitydemanded.Prediction:sellerswillcompeteamongstthemselves,drivingthepricedown.Figure3.8TheEffectofSurplusesandShortagesontheMarketPrice(2of2)Nowwhatifthepricewere$0.50?Atapriceof$0.50,consumerswanttobuy7millionbottles,whileproducerswanttosell3million.Thisgivesashortage

of4millionbottles;asituationinwhichquantitydemandedisgreaterthanquantitysupplied.Prediction:sellerswillrealizetheycanincreasethepriceandstillsellasmanybottlesofwater,sothepricewillrise.DemandandSupplyBothCountPriceisdeterminedbytheinteractionofbuyersandsellers.Neithergroupcandictatepriceinacompetitivemarket(i.e.onewithmanybuyersandsellers).Howeverchangesinsupplyand/ordemandwillaffectthepriceandquantitytraded.3.4TheEffectofDemandandSupplyShiftsonEquilibriumUsedemandandsupplygraphstopredictchangesinpricesandquantities.Predictionsaboutpriceandquantityinourmodelrequireustoknowsupplyanddemandcurves.Typically,weknowpriceandquantitybutdonotknowthecurvesthatgeneratethem.Thepowerofthedemandandsupplymodelisinitsabilitytopredictdirectional

changesinpriceandquantitytraded.Figure3.9TheEffectofanIncreaseinDemandonEquilibriumSupposeincomesincrease.Whathappenstotheequilibriuminthepremiumbottledwatermarket?Bottledwaterisanormalgood,soasincomerises,demandshiftstotheright(D1toD2).Equilibriumpricerises(P1toP2).Equilibriumquantityrises(Q1toQ2).Figure3.10TheEffectofanIncreaseinSupplyonEquilibrium(1of2)ThegraphshowsthemarketforpremiumbottledwaterbeforePepsiCoentersthemarket.WhenPepsiCoenters,morebottlesaresuppliedatanygivenprice—anincreaseinsupplyfromS1toS2.EquilibriumpricefallsfromP1toP2.EquilibriumquantityrisesfromQ1toQ2.Figure3.10TheEffectofanIncreaseinSupplyonEquilibrium(2of2)Byhowmuchwillpricefall?Byhowmuchwillquantityrise?Wecannotsay,withoutknowingmoreinformation.Fornow,wecanonlypredictthatpricewillfallandquantitytradedwillrise.Table3.3HowShiftsinDemandandSupplyAffectEquilibriumPrice(P)andQuantity(Q)(1of2)BlankSupplyCurveUnchangedSupplyCurveShiftstotheRightSupplyCurveShiftstotheLeftDemandCurveUnchangedQunchangedPunchangedQincreasesPdecreasesQdecreasesPincreasesDemandCurveShiftstotheRightQincreasesPincreasesBlankBlankDemandCurveShiftstotheLeftQdecreasesPdecreasesBlankBlankThetablesummarizeswhathappenswhenthedemandcurveshiftsorthesupplycurveshifts,withtheothercurveremainingunchanged.ApplytheConcept:LowerDemandforOrangeJuice—ButHigherPrices?(1of2)From2011to2016,salesoforangejuiceintheU.S.fellbymorethan15%.ADeutscheBankanalystin2017claimed“Peopleareshiftingtolow-calorie,naturalproducts.”Withoutanyotherchange,thiswouldleadtothepriceoforangejuicefalling.Butthepricehasbeenrising;inearly2017,a64-ozbottleoforangejuicecostabout$4.00,upfrom$3.25twoyearsearlier.Whatmusthavebeenhappeningatthesametimeasthedecreaseindemandfororangejuice?ApplytheConcept:LowerDemandforOrangeJuice—ButHigherPrices?(2of2)AcitrusdiseasecalledcitrusgreeningreducedsupplyoforangesintheU.S.andBrazil,thetwoleadingorangegrowingcountries.Becausethedecreaseinsupplywaslargerthanthedecreaseindemand,pricesroseoverall.Figure3.11ShiftsinDemandandSupplyoverTime(1of3)Overtime,itislikelythatbothdemandandsupplywillchange.Forexample,asnewfirmsenterthemarketforpremiumbottledwaterandincomesincrease,weexpect:Thesupplycurvewillshifttotheright,andThedemandcurvewillshifttotheright.Figure3.11ShiftsinDemandandSupplyoverTime(2of3)Whatdoesourmodelpredict?S↑→

(P↓andQ↑)D