chap20宏观经济学曼昆

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SHORT-RUNECONOMICFLUCTUATIONS短期经济波动20AggregateDemandandAggregateSupply总需求与总供给本章我们将探索这些问题的答案：什么是经济波动？它们的特点是什么？总需求与总供给模型如何解释经济波动？为什么总需求曲线向右下方倾斜？什么使总需求曲线移动？短期总供给曲线的斜率是多少？长期的呢？什么使总供给曲线移动？3Short-RunEconomicFluctuationsEconomicactivityfluctuatesfromyeartoyear.Inmostyearsproductionofgoodsandservicesrises.Onaverageoverthepast50years,productionintheU.S.economyhasgrownbyabout3percentperyear.Insomeyearsnormalgrowthdoesnotoccur,causingarecession.短期经济波动经济活动每年都有波动。在大多数年份，物品与劳务的产量增加了。在过去的50年间，美国经济的产量平均每年增长3%左右。在一些年份，并没有出现这种正常增长，导致衰退。Short-RunEconomicFluctuations

短期经济波动Arecession

isaperiodofdecliningrealincomes,andrisingunemployment.衰退——实际GDP下降和失业增加的时期。Adepression

isasevererecession.萧条——严重的衰退。20.1THREEKEYFACTSABOUTECONOMICFLUCTUATIONS(1)Economicfluctuationsareirregularandunpredictable.Fluctuationsintheeconomyareoftencalledthebusinesscycle.(2)Mostmacroeconomicvariablesfluctuatetogether.(3)Asoutputfalls,unemploymentrises.20.1关于经济波动的三个事实(1)经济波动是无规律的和无法预测的。经济中的波动通常被称为经济周期。(2)大多数宏观经济变量同时波动。(3)随着产量减少，失业增加。Figure1ALookAtShort-RunEconomicFluctuationsBillionsof1996DollarsRealGDP(a)RealGDP$10,0009,0008,0007,0006,0005,0004,0003,0002,00019651970197519801985199019952000图1.观察短期经济波动1996的10亿美元RealGDP(a)实际GDP$10,0009,0008,0007,0006,0005,0004,0003,0002,00019651970197519801985199019952000Mostmacroeconomicvariablesfluctuatetogether大多数宏观经济变量一起波动.Mostmacroeconomicvariablesthatmeasuresometypeofincomeorproductionfluctuatecloselytogether大多数衡量某种收入或产出的宏观经济变量同时波动.Althoughmanymacroeconomicvariablesfluctuatetogether,theyfluctuatebydifferentamounts尽管很多宏观经济变量一起波动，但是它们波动的大小并不同.Figure1ALookAtShort-RunEconomicFluctuationsBillionsof1996Dollars(b)InvestmentSpending$1,8001,6001,4001,2001,00080060040020019651970197519801985199019952000Investmentspending图1.观察短期经济波动(b)投资支出$1,8001,6001,4001,2001,00080060040020019651970197519801985199019952000Investmentspending1996的10亿美元Asoutputfalls,unemploymentrises随着产量减少，失业增加.ChangesinrealGDPareinverselyrelatedtochangesintheunemploymentrate实际GDP的变化与失业率的变化是反向相关的.Duringtimesofrecession,unemploymentrisessubstantially在衰退期间，失业率大幅上升.Figure1ALookAtShort-RunEconomicFluctuationsPercentofLaborForce(c)UnemploymentRate02468101219651970197519801985199019952000UnemploymentrateCopyright©2004South-Western图1.观察短期经济波动劳动力的百分比(c)失业率02468101219651970197519801985199019952000Unemploymentrate20.2EXPLAININGSHORT-RUNECONOMICFLUCTUATIONS(1)HowtheShortRunDiffersfromtheLongRunMosteconomistsbelievethatclassicaltheorydescribestheworldinthelongrunbutnotintheshortrun.Changesinthemoneysupplyaffectnominalvariablesbutnotrealvariablesinthelongrun.Theassumptionofmonetaryneutralityisnotappropriatewhenstudyingyear-to-yearchangesintheeconomy.20.2解释短期经济波动(1)长期与短期有什么不同大多数经济学家认为，古典经济理论描述长期世界，并不描述短期世界。在长期中，货币供给的变化影响名义变量，而不影响实际变量。在研究逐年的经济变动时，货币中性的假设就不再适用了。TheBasicModelofEconomicFluctuations(2)Twovariablesareusedtodevelopamodeltoanalyzetheshort-runfluctuations.Theeconomy’soutputofgoodsandservicesmeasuredbyrealGDP.TheoverallpricelevelmeasuredbytheCPIortheGDPdeflator.经济波动的基本模型(2)两个变量被用来建立模型分析短期经济波动。用实际GDP衡量的经济中的物品与劳务的产量。用CPI或GDP平减指数衡量的物价总水平。(3)TheBasicModelofEconomicFluctuations

经济波动的基本模型TheBasicModelofAggregateDemandandAggregateSupply

总需求与总供给基本模型Economistusethemodelofaggregatedemandandaggregatesupply

toexplainshort-runfluctuationsineconomicactivityarounditslong-runtrend.

经济学家用总需求与总供给模型来解释经济活动围绕其长期趋势的短期波动的模型。Theaggregate-demandcurve

showsthequantityofgoodsandservicesthathouseholds,firms,andthegovernmentwanttobuyateachpricelevel.总需求曲线——一条表示在每一种物价水平时家庭、企业和政府想要购买的物品与劳务量的曲线。Theaggregate-supplycurve

showsthequantityofgoodsandservicesthatfirmschoosetoproduceandsellateachpricelevel.总供给曲线——一条表示在每一种物价水平下企业选择生产并销售的物品与劳务量的曲线。Figure2AggregateDemandandAggregateSupply...QuantityofOutputPriceLevel0AggregatesupplyAggregatedemandEquilibriumoutputEquilibriumpricelevel图2.总需求与总供给…产量物价水平0总供给总需求均衡产量均衡物价水平20.3TheAggregateDemandCurve

总需求曲线ThefourcomponentsofGDP(Y)contributetotheaggregatedemandforgoodsandservices.

GDP(Y)的四个组成部分对物品与劳务的总需求做贡献。Y=C+I+G+NXFigure3TheAggregate-DemandCurve...QuantityofOutputPriceLevel0AggregatedemandPYY2P21.Adecreaseinthepricelevel...2....increasesthequantityofgoodsandservicesdemanded.图3.总需求曲线…产量物价水平0总需求PYY2P21.物价水平下降...2.…物品与劳务量增加20.3.1WhytheAggregate-DemandCurveIsDownwardSloping

为什么总需求曲线向右下方倾斜（1）ThePriceLevelandConsumption——TheWealthEffect物价水平与消费——财富效应（2）ThePriceLevelandInvestment——TheInterestRateEffect物价水平与投资——利率效应（3）ThePriceLevelandNetExports——TheExchange-RateEffect物价水平与净出口——汇率效应（1）ThePriceLevelandConsumption:TheWealthEffect物价水平与消费:财富效应Adecreaseinthepricelevelmakesconsumersfeelmorewealthy,whichinturnencouragesthemtospendmore.物价水平下降使消费者感到更富裕，这又鼓励他们更多地支出。

Thisincreaseinconsumerspendingmeanslargerquantitiesofgoodsandservicesdemanded.消费支出增加意味着物品与劳务的需求量更大了。（2）ThePriceLevelandInvestment:TheInterestRateEffect物价水平与投资:利率效应Alowerpricelevelreducestheinterestrate,whichencouragesgreaterspendingoninvestmentgoods.较低的物价水平降低了利率，鼓励了更多地支出用在投资物品上Thisincreaseininvestmentspendingmeansalargerquantityofgoodsandservicesdemanded.这种投资支出的增加意味着物品与劳务的需求量更大了（3）ThePriceLevelandNetExports:TheExchange-RateEffect物价水平与净出口：汇率效应WhenafallintheU.S.pricelevelcausesU.S.interestratestofall,therealexchangeratedepreciates,whichstimulatesU.S.netexports.当美国物价水平下降引起美国利率下降时，实际汇率贬值，而且这种贬值刺激了美国的净出口。Theincreaseinnetexportspendingmeansalargerquantityofgoodsandservicesdemanded.净出口开支的增加意味着物品与劳务的需求量更大了20.3.2WhytheAggregate-DemandCurveMightShiftThedownwardslopeoftheaggregatedemandcurveshowsthatafallinthepricelevelraisestheoverallquantityofgoodsandservicesdemanded.Manyotherfactors,however,affectthequantityofgoodsandservicesdemandedatanygivenpricelevel.Whenoneoftheseotherfactorschanges,theaggregatedemandcurveshifts.20.3.2为什么总需求曲线会移动总需求曲线向右下方倾斜表明物价水平下降增加了物品与劳务的总需求量。但是，许多其他因素也影响既定物价水平时的物品与劳务的需求量。

当这些因素中的一种变动时，总需求曲线移动。Shiftsarisingfrom

移动起因于Consumption消费Investment投资GovernmentPurchases政府购买NetExports净出口ShiftsintheAggregateDemandCurveQuantityofOutputPriceLevel0Aggregatedemand,D1P1Y1D2Y2总需求曲线的移动产出物价水平0总需求,D1P1Y1D2Y2在下列各种情形中，总需求曲线会发生什么变动？A. 一个十年期的投资税收优惠到期B. 美元汇率下降C. 物价水平的下降增加了消费者财富的真实价值D. 州政府对利息，红利和资本收益征收新税以取代销售税课堂练习1

总需求曲线37A. 一个十年期的投资税收优惠到期

投资减少，总需求曲线向左移动B.美元汇率下降

净出口增加，总需求曲线向右移动C. 物价水平的下降增加了消费者财富的真实价值

沿总需求曲线移动（财富效应）D. 州政府对利息，红利和资本收益征收新税以取代销售税

消费增加，总需求曲线向右移动

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参考答案3820.4THEAGGREGATE-SUPPLYCURVE

总供给曲线Inthelongrun,theaggregate-supplycurveisvertical.

在长期中，总供给曲线是垂直的。Intheshortrun,theaggregate-supplycurveisupwardsloping.

在短期中，总供给曲线是向右上方倾斜的。TheLong-RunAggregate-SupplyCurveInthelongrun,aneconomy’sproductionofgoodsandservicesdependsonitssuppliesoflabor,capital,andnaturalresourcesandontheavailabletechnologyusedtoturnthesefactorsofproductionintogoodsandservices.Thepriceleveldoesnotaffectthesevariablesinthelongrun.20.4.1WhytheLong-Runaggregate-supplycurveisvertical.长期总供给曲线在长期中，一个经济的物品与劳务供给取决于它的资本、劳动和自然资源的供给，以及用来把资本与劳动变为物品与劳务的生产技术。

在长期中，物价水平并不影响这些变量。20.4.1为什么长期总供给曲线是垂直的Figure4TheLong-RunAggregate-SupplyCurveQuantityofOutputNaturalrateofoutputPriceLevel0Long-runaggregatesupplyP21.Achangeinthepricelevel...2....doesnotaffectthequantityofgoodsandservicessuppliedinthelongrun.P图4.长期总供给曲线产量自然产量率物价水平0长期总供给P21.物价水平变动…2...并不影响长期中物品与劳务的供給量PTheLong-RunAggregate-SupplyCurve长期总供给曲线Thelong-runaggregate-supplycurveisverticalatthenaturalrateofoutput.长期总供给曲线是在自然产量率时的一条垂线。Thislevelofproductionisalsoreferredtoaspotentialoutputorfull-employmentoutput.这一产量水平也被称为潜在产量或充分就业产量。20.4.2WhytheLong-RunAggregate-SupplyCurveMightShift

为什么长期总供给曲线会移动Anychangeintheeconomythataltersthenaturalrateofoutputshiftsthelong-runaggregate-supplycurve.经济中任何改变自然产量率的变动都会使长期总供给曲线移动。Theshiftsmaybecategorizedaccordingtothevariousfactorsintheclassicalmodelthataffectoutput.可以根据古典模型中影响产量的各种因素把这些移动进行归类。Shiftsarisingfrom

移动起因于Labor劳动Capital资本NaturalResources自然资源TechnologicalKnowledge技术知识20.4.3ANewWaytoDepictLong-RunGrowthandInflation

描述长期增长与通货膨胀的新方法Short-runfluctuationsinoutputandpricelevelshouldbeviewedasdeviationsfromthecontinuinglong-runtrends.

应该把短期产量与物价水平波动作为与持续的长期趋势的背离。Figure5Long-RunGrowthandInflationQuantityofOutputY1980AD1980AD1990AggregateDemand,AD2000PriceLevel0Long-runaggregatesupply,LRAS1980Y1990LRAS1990Y2000LRAS2000P19801.Inthelongrun,technologicalprogressshiftslong-runaggregatesupply...4....andongoinginflation.3....leadingtogrowthinoutput...P1990P20002....andgrowthinthemoneysupplyshiftsaggregatedemand...图5.长期增长与通货膨胀产量Y1980AD1980AD1990总需求AD2000物价水平0长期总供给LRAS1980Y1990LRAS1990Y2000LRAS2000P19801.在长期中，技术进步使长期总供给移动….4.....及持续的通货膨胀.3.....引起产量增长….P1990P20002.....以及货币供给增长使总需求移动…20.4.4WhytheAggregate-SupplyCurveSlopesUpwardintheShortRun

为什么短期中总供给曲线向右上方倾斜Intheshortrun,anincreaseintheoveralllevelofpricesintheeconomytendstoraisethequantityofgoodsandservicessupplied.在短期中,经济中物价总水平的上升倾向于增加物品与劳务的供給量。Adecreaseinthelevelofpricestendstoreducethequantityofgoodsandservicessupplied.物价总水平的下降倾向于减少物品与劳务的供給量。Figure6TheShort-RunAggregate-SupplyCurveQuantityofOutputPriceLevel0Short-runaggregatesupply1.Adecreaseinthepricelevel...2....reducesthequantityofgoodsandservicessuppliedintheshortrun.YPY2P2图6.短期总供给曲线产量物价水平0短期总供给1.物价水平下降….减少了短期中物品与劳务的供給量。YPY2P2Why

theAggregate-SupplyCurveSlopesUpwardintheShortRun

为什么短期中总供给曲线向右上方倾斜TheMisperceptionsTheory

错觉理论TheSticky-WageTheory粘性工资理论TheSticky-PriceTheory粘性价格理论（1）TheMisperceptionsTheoryChangesintheoverallpriceleveltemporarilymisleadsuppliersaboutwhatishappeninginthemarketsinwhichtheyselltheiroutput:Alowerpricelevelcausesmisperceptionsaboutrelativeprices.Thesemisperceptionsinducesupplierstodecreasethequantityofgoodsandservicessupplied.

（1）错觉理论物价总水平的变动会暂时误导供给者对他们出售其产品的市场发生的变动的看法:低物价水平引起对相对价格的错觉。这些错觉引起供给者减少物品与劳务的供給量。（2）TheSticky-WageTheoryNominalwagesareslowtoadjust,orare“sticky”intheshortrun:Wagesdonotadjustimmediatelytoafallinthepricelevel.Alowerpricelevelmakesemploymentandproductionlessprofitable.Thisinducesfirmstoreducethequantityofgoodsandservicessupplied.（2）粘性工资理论名义工资调整缓慢，或者说在短期中是“粘性的”:工资不能根据物价水平迅速调整。较低的物价水平使就业和生产不利。这就引起企业减少物品与劳务的供給量。（3）TheSticky-PriceTheory

Pricesofsomegoodsandservicesadjustsluggishlyinresponsetochangingeconomicconditions:Anunexpectedfallinthepricelevelleavessomefirmswithhigher-than-desiredprices.Thisdepressessales,whichinducesfirmstoreducethequantityofgoodsandservicestheyproduce.（3）粘性价格理论

一些物品与劳务的价格对经济状况变动的调整也是缓慢的:未预期到的物价水平下降使一些企业的价格高于合意水平。这就抑制了销售，并引起企业减少它们生产的物品与劳务量。20.4.5WhytheShort-RunAggregate-SupplyCurveMightShift

为什么短期总供给曲线会移动Shiftsarisingfrom

移动起因于Labor劳动Capital资本NaturalResources.自然资源Technology.技术ExpectedPriceLevel.预期物价水平Anincreaseintheexpectedpricelevelreducesthequantityofgoodsandservicessuppliedandshiftstheshort-runaggregatesupplycurvetotheleft.预期物价水平上升减少了物品与劳务供給量，并使短期总供给曲线向左移动。Adecreaseintheexpectedpricelevelraisesthequantityofgoodsandservicessuppliedandshiftstheshort-runaggregatesupplycurvetotheright.预期物价水平下降增加了物品与劳务供給量，并使短期总供给曲线向右移动。Figure7TheLong-RunEquilibriumNaturalrateofoutputQuantityofOutputPriceLevel0Short-runaggregatesupplyLong-runaggregatesupplyAggregatedemandAEquilibriumprice图7.长期均衡自然产量率产量物价水平0短期总供给长期总供给总需求A均衡价格20.5TWOCAUSESOFECONOMICFLUCTUATIONS（1）ShiftsinAggregateDemandIntheshortrun,shiftsinaggregatedemandcausefluctuationsintheeconomy’soutputofgoodsandservices.Inthelongrun,shiftsinaggregatedemandaffecttheoverallpricelevelbutdonotaffectoutput.20.5经济波动的两个原因（1）总需求移动在短期中，总需求移动引起经济中物品与劳务产量的波动。在长期中，总需求移动影响物价总水平，但不影响产量。Figure8AContractioninAggregateDemandQuantityofOutputPriceLevel0Short-runaggregatesupply,ASLong-runaggregatesupplyAggregatedemand,ADAPYAD2AS21.Adecreaseinaggregatedemand...2....causesoutputtofallintheshortrun...3....butovertime,theshort-runaggregate-supplycurveshifts...4....andoutputreturnstoitsnaturalrate.CP3BP2Y2图8.总需求减少产量物价水平0短期总供给,AS1长期总供给总需求,ADAPYAD2AS21.总需求减少…..2....引起短期中产量减少

...3……但随着时间推移，短期总供给曲线移动……4……产量恢复到其自然产量率水平。CP3BP2Y2画出美国经济的AD-SRAS-LRAS图形，从经济的长期均衡开始加拿大出现经济繁荣，用你的图形分析这对美国GDP，物价水平和失业率的短期与长期影响课堂练习

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模型的应用68课堂练习

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参考答案69LRASYNPYAD2SRAS2AD1SRAS1P1P3CP2Y2BA事件：加拿大经济繁荣1.影响

NX，AD曲线2. AD曲线向右移动3. 短期均衡在点B。P与Y

增加，失业率降低4. 随时间的推移，PE上升，SRAS曲线一直向左移动，直到达到长期均衡点C。Y与失业率回到起始水平0（2）AnAdverseShiftinAggregateSupplyAdecreaseinoneofthedeterminantsofaggregatesupplyshiftsthecurvetotheleft:Outputfallsbelowthenaturalrateofemployment.Unemploymentrises.Thepricelevelrises.（2）总供给的不利移动总供给决定因素中任何一种降低都使总供给曲线向左移动:产量下降到自然就业率水平以下。失业率上升。物价水平上涨。Figure10An

AdverseShiftinAggregateSupplyQuantityofOutputPriceLevel0Aggregatedemand3....andthepriceleveltorise.2....causesoutputtofall...1.Anadverseshiftintheshort-runaggregate-supplycurve...Short-runaggregatesupply,ASLong-runaggregatesupplyYAPAS2BY2P2图10.总供给的不利移动产量物价水平0总需求3....以及物价水平上升。2....引起产量减少...1.短期总供给曲线的不利移动……短期总供给AS长期总供给YAPAS2BY2P2TheEffectsofaShiftinAggregateSupply（1）StagflationAdverseshiftsinaggregatesupplycausestagflation—aperiodofrecessionandinflation.Outputfallsandpricesrise.Policymakerswhocaninfluenceaggregatedemandcannotoffsetbothoftheseadverseeffectssimultaneously.总供给移动的影响（1）滞胀总供给的不利移动会引起滞胀—衰退和通货膨胀并存的时期。产量减少而物价上升。那些能影响总需求的决策者不能同时抵消这两种不利的影响。（2）PolicyResponsestoRecessionPolicymakersmayrespondtoarecessioninoneofthefollowingways:Donothingandwaitforpricesandwagestoadjust.Takeactiontoincreaseaggregatedemandbyusingmonetaryandfiscalpolicy.总供给移动的影响（2）对付衰退的政策政策制定者可以用下列手段之一来对付衰退:什么也不做，等待价格和工资调整。利用货币和财政政策增加总需求。Figure11AccommodatinganAdverseShiftinAggregateSupplyQuantityofOutputNaturalrateofoutputPriceLevel0Short-runaggregatesupply,ASLong-runaggregatesupplyAggregatedemand,ADP2APAS23....whichcausesthepriceleveltorisefurther...4....butkeepsoutputatitsnaturalrate.2....policymakerscanaccommodatetheshiftbyexpandingaggregatedemand...1.Whenshort-runaggregatesupplyfalls...AD2CP3图11.抵消总供给的不利移动产量自然产量率物价水平0短期总供给AS长期总供给总需求,ADP2APAS23....这引起物价水平进一步上升……4....但产量保持在自然产量率水平2....决策者可以通过扩大总需求来抵消这种移动……1.当短期总供给减少时…AD2CP3SummaryAllsocietiesexperienceshort-runeconomicfluctuationsaroundlong-runtrends.Thesefluctuationsareirregularandlargelyunpredictable.Whenrecessionsoccur,re