曼昆經濟學原理第四章

2

SUPPLYANDDEMANDI:HOWMARKETSWORK供給與需求（I）：市場如何運行TheMarketForcesofSupplyandDemand

供給與需求的市場力量Chapter4TheMarketForcesofSupplyandDemandSupply

and

demand

arethetwowordsthateconomistsusemostoften.Supply

and

demand

aretheforcesthatmakemarketeconomieswork.Modernmicroeconomicsisaboutsupply,demand,andmarketequilibrium.供給與需求的市場力量供給和需求是經濟學家最常用的兩個詞。供給和需求是讓市場經濟運行的力量?，F代微觀經濟學就是關于供給、需求和市場均衡的學科。Markets

Amarketisagroupofbuyersandsellersofaparticulargoodorservice.Thetermssupplyanddemandrefertothebehaviorofpeople...astheyinteractwithoneanotherinmarkets.市場

市場是指某種物品或勞務的一群買者與賣者的集合。

供給與需求這兩個術語是指人們在市場上相互交易時的行為。Marketsandcompetition

市場與競爭

Buyers

determine

demand.買者決定需求

Sellers

determine

supply.賣者決定供給ACompetitiveMarket競爭市場Acompetitivemarketisamarketinwhichtherearemanybuyersandsellerssothateachhasanegligibleimpactonthemarketprice

競爭市場——有很多買者和賣者的市場，所以每一個買者或賣者對市場價格的影響都可以忽略不計。Competition:PerfectandOtherwiseProductsarethesameNumerousbuyersandsellerssothateachhasnoinfluenceoverpriceBuyersandSellersarepricetakersPerfectCompetition競爭:完全及其它產品是完全相同的。買者和賣者如此之多，以至于沒有一個買者或賣者可以影響價格。買者和賣者都是價格接受者。完全競爭Competition:PerfectandOtherwiseMonopolyOneseller,andsellercontrolspriceOligopolyFewsellersNotalwaysaggressivecompetition競爭:完全及其它壟斷一個賣者，賣者決定價格。寡頭少數幾個賣者。并不總是主動地進行競爭。Competition:PerfectandOtherwiseMonopolisticCompetitionManysellersSlightlydifferentiatedproductsEachsellermaysetpriceforitsownproduct競爭:完全及其它壟斷競爭許多賣者略有差異的產品每個賣者都有決定自己產品價格的能力Demand需求Quantitydemanded

istheamount

ofagoodthatbuyersarewillingandabletopurchase.

需求量是指買者愿意而且能夠購買的一種物品或勞務的數量。LawofDemand需求規(guī)律Thelawofdemandstatesthatthereisaninverserelationshipbetweenpriceandquantitydemanded.

需求規(guī)律認為，價格與需求量之間的關系是負關系。DemandSchedule需求表Thedemandscheduleisatablethatshowstherelationshipbetweenthe

price

ofthegoodandthe

quantity

demanded.

需求表

——

表示一種物品的價格與需求量之間關系的表格。Catherine’sDemandSchedule凱瑟琳的需求表DemandCurve需求曲線The

demandcurve

is

thedownward-slopinglinerelatingpricetoquantitydemanded.需求曲線——把價格與需求量聯系在一起的向右下方傾斜的曲線。Figure1Catherine’sDemandSchedule

andDemandCurvePriceofIce-CreamCone02.502.001.501.000.501234567891011QuantityofIce-CreamCones$3.00121.Adecreaseinprice...2....increasesquantityofconesdemanded.圖1.Catherine的需求表和需求曲線冰激凌蛋卷的價格02.502.001.501.000.501234567891011冰激凌蛋卷需求量$3.00121.價格下降…

2....蛋卷的需求量上升。MarketDemandversusIndividualDemandMarketdemandreferstothesumofallindividualdemandsforaparticulargoodorservice.Graphically,individualdemandcurvesaresummedhorizontallytoobtainthemarketdemandcurve.市場需求市場需求是指所有個人對某種物品或勞務需求的總和。從圖形上看,把個人需求曲線水平相加，就得出了市場需求曲線。ChangeinQuantityDemandedversusChangeinDemandChangein

QuantityDemandedMovementalongthedemandcurve.Causedbyachangeinthepriceof theproduct.需求量的變化與需求的變化需求量的變化沿著需求曲線移動。是由于產品價格變動引起的。0DPriceofIce-Cream

ConesQuantityofIce-CreamConesAtaxthatraisesthepriceofice-creamconesresultsinamovementalongthedemandcurve.AB81.00$2.004ChangesinQuantityDemanded0D冰激凌蛋卷的價格冰激凌蛋卷的消費量提高冰激凌蛋卷價格的稅收引起沿著需求曲線的移動AB81.00$2.004需求量的變化ShiftsintheDemandCurveConsumerincomePricesofrelatedgoodsTastesExpectationsNumberofbuyers需求曲線的移動消費者收入相關產品價格嗜好預期買者數量ShiftsintheDemandCurveChangeinDemandAshiftinthedemandcurve,either totheleftorright.Causedbyachangeina determinantotherthantheprice.需求曲線的移動需求的變化需求曲線的移動，向左或者向右。是由價格以外的因素變化引起的。ShiftsintheDemandCurve0D1PriceofIce-CreamConeQuantityofIce-CreamConesD3D2IncreaseindemandDecreaseindemand需求曲線的移動0D1冰激凌蛋卷的價格冰激凌蛋卷的數量D3D2需求增加需求減少ConsumerIncome消費者收入Asincomeincreasesthedemandforanormalgoodwillincrease.

收入增加，正常商品的需求增加Asincomeincreasesthedemandforaninferiorgoodwilldecrease.

收入增加，劣等品的需求減少ConsumerIncome

NormalGood$3.002.502.001.501.000.50213456789101211PriceofIce-CreamConeQuantityofIce-CreamCones0IncreaseindemandAnincreaseinincome...D1D2消費者收入正常商品$3.002.502.001.501.000.50213456789101211冰激凌蛋卷的價格冰激凌蛋卷的數量0需求增加收入增加...D1D2ConsumerIncome

InferiorGood$3.002.502.001.501.000.50213456789101211PriceofIce-CreamConeQuantityofIce-CreamCones0DecreaseindemandAnincreaseinincome...D1D2消費者收入劣等品$3.002.502.001.501.000.50213456789101211冰激凌蛋卷的價格冰激凌蛋卷的數量0需求減少收入增加...D1D2PricesofRelatedGoods

Substitutes&ComplementsWhenafallinthepriceofonegoodreduces

thedemandforanothergood,thetwogoodsarecalledsubstitutes.Whenafallinthepriceofonegoodincreases

thedemandforanothergood,thetwogoodsarecalledcomplements.相關物品的價格

替代品和互補品當一種物品價格下降減少了另一種物品需求時，這兩種物品被稱為替代品。當一種物品價格下降增加了另一種物品需求時，這兩種物品被稱為互補品。Table1VariablesThatInfluenceBuyersCopyright?2004South-Western表1.影響買者的變量變量這些變量的變動將...價格表現為沿著需求曲線的變動收入移動需求曲線相關物品價格移動需求曲線嗜好移動需求曲線預期移動需求曲線買者數量移動需求曲線Supply供給Quantitysupplied

istheamountofagoodthatsellersarewillingandabletosell.

供給量是指賣者愿意而且能夠出售的一種物品或勞務的數量。LawofSupply供給規(guī)律The

lawofsupply

statesthatthereisadirect(positive)relationshipbetweenpriceandquantity

supplied.供給規(guī)律認為，價格與供給量之間的關系是正關系。SupplySchedule供給表The

supplyschedule

is

atablethatshowstherelationshipbetweenthepriceofthegoodandthequantitysupplied.供給表是表示一種物品價格與供給量之間關系的表格。

Ben’sSupplySchedule供給表SupplyCurve供給曲線The

supplycurve

istheupward-slopinglinerelatingpricetoquantitysupplied.

供給曲線——把價格與供給量聯系在一起的向右上方傾斜的曲線。Figure5Ben’sSupplySchedule

andSupplyCurvericeofIce-CreamCone02.502.001.501.001234567891011QuantityofIce-CreamCones$3.00120.501.Anincrease

inprice...2....

increasesquantityofconessupplied.圖5.Ben供給表與供給曲線冰激凌蛋卷需求量02.502.001.501.001234567891011冰激凌蛋卷的供給量$3.00120.501.價格上升…

2....供給量增加。MarketSupplyversusIndividualSupplyMarketsupplyreferstothesumofallindividualsuppliesforallsellersofaparticulargoodorservice.Graphically,individualsupplycurvesaresummedhorizontallytoobtainthemarketsupplycurve.市場供給市場供給是指某種物品或勞務的所有賣者個人供給的總和。從圖形上看,把個人供給曲線水平相加，就得出了市場供給曲線。ShiftsintheSupplyCurveInputpricesTechnologyExpectationsNumberofproducers供給曲線的移動投入要素價格技術預期生產者數量ChangeinQuantitySuppliedversusChangeinSupplyChangeinQuantitySuppliedMovementalongthesupplycurve.Causedbyachangeinthemarketpriceoftheproduct.供給量的變化與供給的變化供給量的變化沿著供給曲線移動。是由于產品的市場價格變動引起的。ChangeinQuantitySupplied15PriceofIce-CreamConeQuantityofIce-CreamCones0S1.00AC$3.00Ariseinthepriceoficecreamconesresultsinamovementalongthesupplycurve.供給量的變化15冰激凌蛋卷的價格冰激凌蛋卷的數量0S1.00AC$3.00冰激凌蛋卷的市場價格上升導致供給量沿著供給曲線的移動。ShiftsintheSupplyCurveChangeinSupplyAshiftinthesupplycurve,eithertotheleftorright.

Causedbyachangeinadeterminantotherthanprice.供給曲線的移動供給的變化供給曲線的移動，向左或者向右。

是由于價格以外的因素變化造成的。Shifts

intheSupplyCurvePriceofIce-CreamConeQuantityofIce-CreamCones0S1S2S3IncreaseinSupplyDecreaseinSupply供給曲線的移動冰激凌蛋卷的價格冰激凌蛋卷的數量0S1S2S3供給增加供給減少Table2VariablesThatInfluenceSellers供給量的變化與供給的變化SUPPLYANDDEMANDTOGETHER

供給與需求的結合Equilibrium

referstoasituationinwhichthepricehasreachedthelevelwherequantitysuppliedequalsquantitydemanded.

市場均衡——

價格水平達到供給量與需求量相等的狀態(tài)。SupplyandDemandTogetherEquilibriumPriceThepricethatbalancessupplyanddemand.Onagraph,itisthepriceatwhichthesupplyanddemandcurvesintersect.EquilibriumQuantityThequantitythatbalancessupplyanddemand.Onagraphitisthequantityatwhichthesupplyanddemandcurvesintersect.

供給與需求的結合均衡價格使供給與需求平衡的價格。從圖形上看，就是供給曲線與需求曲線相交時的價格。均衡數量當價格調整到使供給與需求平衡時的供給量與需求量。從圖形上看，就是供給曲線與需求曲線相交時的數量。

SupplyandDemandTogetherDemandScheduleSupplyScheduleAt$2.00,thequantitydemandedisequaltothequantitysupplied!供給與需求的結合需求表供給表在$2.00時,需求量等于供給量!Figure8TheEquilibriumofSupply

andDemandCopyright?2003Southwestern/ThomsonLearningPriceofIce-CreamCone0123456789101112QuantityofIce-CreamCones13EquilibriumquantityEquilibriumpriceEquilibriumSupplyDemand$2.00表8.供給與需求的均衡冰激凌蛋卷需求量0123456789101112冰激凌蛋卷的數量13均衡數量均衡價格均衡供給需求$2.00Figure9MarketsNotinEquilibriumPriceofIce-CreamCone0SupplyDemand(a)ExcessSupplyQuantitydemandedQuantitysuppliedSurplusQuantityofIce-CreamCones4$2.50102.007圖9.非均衡狀態(tài)的市場冰激凌蛋卷需求量0供給需求(a)超額供給需求量供給量過剩冰激凌蛋卷的數量4$2.50102.007EquilibriumSurplusWhenprice>equilibriumprice,thenquantitysupplied>quantitydemanded.Thereisexcesssupplyorasurplus.Supplierswilllowerthepricetoincreasesales,therebymovingtowardequilibrium.均衡過剩當價格高于均衡價格時，供給量大于需求量。

存在超額供給或過剩。

供給者通過降低價格來增加銷售，這使價格向其均衡水平變動。EquilibriumShortageWhenprice<equilibriumprice,thenquantitydemanded>thequantitysupplied.

Thereisexcessdemandorashortage.Supplierswillraisethepriceduetotoomanybuyerschasingtoofewgoods,therebymovingtowardequilibrium.均衡短缺當價格低于市場均衡價格時，需求量超過了供給量。

存在著超額需求或短缺。

由于太多賣者要購買太少的物品，供給者將提高價格。因此價格將趨向于市場均衡價格。Figure9MarketsNotinEquilibriumPriceofIce-CreamCone0QuantityofIce-CreamConesSupplyDemand(b)ExcessDemandQuantitysuppliedQuantitydemanded1.5010$2.0074Shortage圖9.非均衡狀態(tài)的市場冰激凌蛋卷需求量0冰激凌蛋卷的數量供給供給(b)超額需求供給量需求量1.5010$2.0074短缺Equilibrium

均衡Lawofsupplyanddemand

需求規(guī)律Theclaimthatthepriceofanygoodadjuststobringthequantitysuppliedandthequantitydemandedforthatgoodintobalance.認為任何一種物品價格的調整都會使該物品供求平衡的觀點。ThreeStepsToAnalyzingChangesinEquilibriumDecidewhethertheeventshiftsthesupplyordemandcurve(orboth).Decidewhetherthecurve(s)shift(s)totheleftortotheright.Usethesupply-and-demanddiagramtoseehowtheshiftaffectsequilibriumpriceandquantity.分析均衡的三個步驟確定該事件是使供給曲線移動，還是使需求曲線移動，或者使兩種曲線都移動。確定曲線是向右移動，還是向左移動。用供求圖來考察這種移動如何影響均衡價格和數量。HowanIncreaseinDemandAffectstheEquilibriumPriceofIce-CreamCone2.0007QuantityofIce-CreamConesSupplyInitialequilibriumD11.Hotweatherincreasesthedemandforicecream...D22....resultinginahigherprice...$2.50103....andahigherquantitysold.Newequilibrium需求增加如何影響均衡冰激凌蛋卷的價格2.0007冰激凌蛋卷的數量供給原來的均衡D11.天氣熱使冰激凌需求增加...D22.…引起價格上升...$2.50103.…及銷售量更多。新均衡ThreeStepstoAnalyzingChangesinEquilibrium

ShiftsinCurvesversusMovementsalongCurvesAshiftinthesupplycurveiscalledachangeinsupply.Amovementalongafixedsupplycurveiscalledachangeinquantitysupplied.Ashiftinthedemandcurveiscalledachangeindemand.Amovementalongafixeddemandcurveiscalledachangeinquantitydemanded.分析均衡的三個步驟曲線移動與沿著曲線的移動:供給曲線的移動被稱為供給的變化。沿著固定的供給曲線的移動被稱為供給量的變化。需求曲線的移動被稱為需求的變化。沿著固定的需求曲線的移動被稱為需求量的變化。S2HowaDecreaseinSupplyAffectstheEquilibriumPriceofIce-CreamCone2.00012347891112QuantityofIce-CreamCones13DemandInitialequilibriumS1101.Anearthquakereducesthesupplyoficecream...Newequilibrium2....resultinginahigherprice...$2.503....andalowerquantitysold.S2供給減少如何影響均衡冰激凌蛋卷的價格2.00012347891112冰激凌蛋卷的數量13需求原來的均衡S110地震減少了冰激凌的供給...新均衡2.…引起價格上升...$2.503.…以及銷售量減少。WhatHappenstoPriceandQuantityWhenSupplyorDemandShifts?當供給或需求變動時，價格和數量

會發(fā)生什么變化?SummaryEconomistsusethemodelofsupplyanddemandtoanalyzecompetitivemarkets.Inacompetitivemarket,therearemanybuyersandsellers,eachofwhomhaslittleornoinfluenceonthemarketprice.小結經濟學家用供求模型來分析競爭市場。在競爭市場中，有許多買者和賣者，他們當中的任何一個對市場價格具有極小或者沒有影響力。SummaryThedemandcurveshowshowthequantityofagooddependsupontheprice.Accordingtothelawofdemand,asthepriceofagoodfalls,thequantitydemandedrises.Therefore,thedemandcurveslopesdownward.Inadditiontoprice,otherdeterminantsofhowmuchconsumerswanttobuyincludeincome,thepricesofcomplementsandsubstitutes,tastes,expectations,andthenumberofbuyers.Ifo