8

SHORT-RUNECONOMICFLUCTUATIONS短期經濟波動20AggregateDemandandAggregateSupply總需求與總供給本章我們將探索這些問題的答案：什么是經濟波動？它們的特點是什么？總需求與總供給模型如何解釋經濟波動？為什么總需求曲線向右下方傾斜？什么使總需求曲線移動？短期總供給曲線的斜率是多少？長期的呢？什么使總供給曲線移動？3Short-RunEconomicFluctuationsEconomicactivityfluctuatesfromyeartoyear.Inmostyearsproductionofgoodsandservicesrises.Onaverageoverthepast50years,productionintheU.S.economyhasgrownbyabout3percentperyear.Insomeyearsnormalgrowthdoesnotoccur,causingarecession.短期經濟波動經濟活動每年都有波動。在大多數年份，物品與勞務的產量增加了。在過去的50年間，美國經濟的產量平均每年增長3%左右。在一些年份，并沒有出現這種正常增長，導致衰退。Short-RunEconomicFluctuations

短期經濟波動Arecession

isaperiodofdecliningrealincomes,andrisingunemployment.衰退——實際GDP下降和失業增加的時期。Adepression

isasevererecession.蕭條——嚴重的衰退。20.1THREEKEYFACTSABOUTECONOMICFLUCTUATIONS(1)Economicfluctuationsareirregularandunpredictable.Fluctuationsintheeconomyareoftencalledthebusinesscycle.(2)Mostmacroeconomicvariablesfluctuatetogether.(3)Asoutputfalls,unemploymentrises.20.1關于經濟波動的三個事實(1)經濟波動是無規律的和無法預測的。經濟中的波動通常被稱為經濟周期。(2)大多數宏觀經濟變量同時波動。(3)隨著產量減少，失業增加。Figure1ALookAtShort-RunEconomicFluctuationsBillionsof1996DollarsRealGDP(a)RealGDP$10,0009,0008,0007,0006,0005,0004,0003,0002,00019651970197519801985199019952000圖1.觀察短期經濟波動1996的10億美元RealGDP(a)實際GDP$10,0009,0008,0007,0006,0005,0004,0003,0002,00019651970197519801985199019952000Mostmacroeconomicvariablesfluctuatetogether大多數宏觀經濟變量一起波動.Mostmacroeconomicvariablesthatmeasuresometypeofincomeorproductionfluctuatecloselytogether大多數衡量某種收入或產出的宏觀經濟變量同時波動.Althoughmanymacroeconomicvariablesfluctuatetogether,theyfluctuatebydifferentamounts盡管很多宏觀經濟變量一起波動，但是它們波動的大小并不同.Figure1ALookAtShort-RunEconomicFluctuationsBillionsof1996Dollars(b)InvestmentSpending$1,8001,6001,4001,2001,00080060040020019651970197519801985199019952000Investmentspending圖1.觀察短期經濟波動(b)投資支出$1,8001,6001,4001,2001,00080060040020019651970197519801985199019952000Investmentspending1996的10億美元Asoutputfalls,unemploymentrises隨著產量減少，失業增加.ChangesinrealGDPareinverselyrelatedtochangesintheunemploymentrate實際GDP的變化與失業率的變化是反向相關的.Duringtimesofrecession,unemploymentrisessubstantially在衰退期間，失業率大幅上升.Figure1ALookAtShort-RunEconomicFluctuationsPercentofLaborForce(c)UnemploymentRate02468101219651970197519801985199019952000UnemploymentrateCopyright?2004South-Western圖1.觀察短期經濟波動勞動力的百分比(c)失業率02468101219651970197519801985199019952000Unemploymentrate20.2EXPLAININGSHORT-RUNECONOMICFLUCTUATIONS(1)HowtheShortRunDiffersfromtheLongRunMosteconomistsbelievethatclassicaltheorydescribestheworldinthelongrunbutnotintheshortrun.Changesinthemoneysupplyaffectnominalvariablesbutnotrealvariablesinthelongrun.Theassumptionofmonetaryneutralityisnotappropriatewhenstudyingyear-to-yearchangesintheeconomy.20.2解釋短期經濟波動(1)長期與短期有什么不同大多數經濟學家認為，古典經濟理論描述長期世界，并不描述短期世界。在長期中，貨幣供給的變化影響名義變量，而不影響實際變量。在研究逐年的經濟變動時，貨幣中性的假設就不再適用了。TheBasicModelofEconomicFluctuations(2)Twovariablesareusedtodevelopamodeltoanalyzetheshort-runfluctuations.Theeconomy’soutputofgoodsandservicesmeasuredbyrealGDP.TheoverallpricelevelmeasuredbytheCPIortheGDPdeflator.經濟波動的基本模型(2)兩個變量被用來建立模型分析短期經濟波動。用實際GDP衡量的經濟中的物品與勞務的產量。用CPI或GDP平減指數衡量的物價總水平。(3)TheBasicModelofEconomicFluctuations

經濟波動的基本模型TheBasicModelofAggregateDemandandAggregateSupply

總需求與總供給基本模型Economistusethemodelofaggregatedemandandaggregatesupply

toexplainshort-runfluctuationsineconomicactivityarounditslong-runtrend.

經濟學家用總需求與總供給模型來解釋經濟活動圍繞其長期趨勢的短期波動的模型。Theaggregate-demandcurve

showsthequantityofgoodsandservicesthathouseholds,firms,andthegovernmentwanttobuyateachpricelevel.總需求曲線——一條表示在每一種物價水平時家庭、企業和政府想要購買的物品與勞務量的曲線。Theaggregate-supplycurve

showsthequantityofgoodsandservicesthatfirmschoosetoproduceandsellateachpricelevel.總供給曲線——一條表示在每一種物價水平下企業選擇生產并銷售的物品與勞務量的曲線。Figure2AggregateDemandandAggregateSupply...QuantityofOutputPriceLevel0AggregatesupplyAggregatedemandEquilibriumoutputEquilibriumpricelevel圖2.總需求與總供給…產量物價水平0總供給總需求均衡產量均衡物價水平20.3TheAggregateDemandCurve

總需求曲線ThefourcomponentsofGDP(Y)contributetotheaggregatedemandforgoodsandservices.

GDP(Y)的四個組成部分對物品與勞務的總需求做貢獻。Y=C+I+G+NXFigure3TheAggregate-DemandCurve...QuantityofOutputPriceLevel0AggregatedemandPYY2P21.Adecreaseinthepricelevel...2....increasesthequantityofgoodsandservicesdemanded.圖3.總需求曲線…產量物價水平0總需求PYY2P21.物價水平下降...2.…物品與勞務量增加20.3.1WhytheAggregate-DemandCurveIsDownwardSloping

為什么總需求曲線向右下方傾斜（1）ThePriceLevelandConsumption——TheWealthEffect物價水平與消費——財富效應（2）ThePriceLevelandInvestment——TheInterestRateEffect物價水平與投資——利率效應（3）ThePriceLevelandNetExports——TheExchange-RateEffect物價水平與凈出口——匯率效應（1）ThePriceLevelandConsumption:TheWealthEffect物價水平與消費:財富效應Adecreaseinthepricelevelmakesconsumersfeelmorewealthy,whichinturnencouragesthemtospendmore.物價水平下降使消費者感到更富裕，這又鼓勵他們更多地支出。

Thisincreaseinconsumerspendingmeanslargerquantitiesofgoodsandservicesdemanded.消費支出增加意味著物品與勞務的需求量更大了。（2）ThePriceLevelandInvestment:TheInterestRateEffect物價水平與投資:利率效應Alowerpricelevelreducestheinterestrate,whichencouragesgreaterspendingoninvestmentgoods.較低的物價水平降低了利率，鼓勵了更多地支出用在投資物品上Thisincreaseininvestmentspendingmeansalargerquantityofgoodsandservicesdemanded.這種投資支出的增加意味著物品與勞務的需求量更大了（3）ThePriceLevelandNetExports:TheExchange-RateEffect物價水平與凈出口：匯率效應WhenafallintheU.S.pricelevelcausesU.S.interestratestofall,therealexchangeratedepreciates,whichstimulatesU.S.netexports.當美國物價水平下降引起美國利率下降時，實際匯率貶值，而且這種貶值刺激了美國的凈出口。Theincreaseinnetexportspendingmeansalargerquantityofgoodsandservicesdemanded.凈出口開支的增加意味著物品與勞務的需求量更大了20.3.2WhytheAggregate-DemandCurveMightShiftThedownwardslopeoftheaggregatedemandcurveshowsthatafallinthepricelevelraisestheoverallquantityofgoodsandservicesdemanded.Manyotherfactors,however,affectthequantityofgoodsandservicesdemandedatanygivenpricelevel.Whenoneoftheseotherfactorschanges,theaggregatedemandcurveshifts.20.3.2為什么總需求曲線會移動總需求曲線向右下方傾斜表明物價水平下降增加了物品與勞務的總需求量。但是，許多其他因素也影響既定物價水平時的物品與勞務的需求量。

當這些因素中的一種變動時，總需求曲線移動。Shiftsarisingfrom

移動起因于Consumption消費Investment投資GovernmentPurchases政府購買NetExports凈出口ShiftsintheAggregateDemandCurveQuantityofOutputPriceLevel0Aggregatedemand,D1P1Y1D2Y2總需求曲線的移動產出物價水平0總需求,D1P1Y1D2Y2在下列各種情形中，總需求曲線會發生什么變動？A. 一個十年期的投資稅收優惠到期B. 美元匯率下降C. 物價水平的下降增加了消費者財富的真實價值D. 州政府對利息，紅利和資本收益征收新稅以取代銷售稅課堂練習1

總需求曲線37A. 一個十年期的投資稅收優惠到期

投資減少，總需求曲線向左移動B.美元匯率下降

凈出口增加，總需求曲線向右移動C. 物價水平的下降增加了消費者財富的真實價值

沿總需求曲線移動（財富效應）D. 州政府對利息，紅利和資本收益征收新稅以取代銷售稅

消費增加，總需求曲線向右移動

課堂練習

1

參考答案3820.4THEAGGREGATE-SUPPLYCURVE

總供給曲線Inthelongrun,theaggregate-supplycurveisvertical.

在長期中，總供給曲線是垂直的。Intheshortrun,theaggregate-supplycurveisupwardsloping.

在短期中，總供給曲線是向右上方傾斜的。TheLong-RunAggregate-SupplyCurveInthelongrun,aneconomy’sproductionofgoodsandservicesdependsonitssuppliesoflabor,capital,andnaturalresourcesandontheavailabletechnologyusedtoturnthesefactorsofproductionintogoodsandservices.Thepriceleveldoesnotaffectthesevariablesinthelongrun.20.4.1WhytheLong-Runaggregate-supplycurveisvertical.長期總供給曲線在長期中，一個經濟的物品與勞務供給取決于它的資本、勞動和自然資源的供給，以及用來把資本與勞動變為物品與勞務的生產技術。

在長期中，物價水平并不影響這些變量。20.4.1為什么長期總供給曲線是垂直的Figure4TheLong-RunAggregate-SupplyCurveQuantityofOutputNaturalrateofoutputPriceLevel0Long-runaggregatesupplyP21.Achangeinthepricelevel...2....doesnotaffectthequantityofgoodsandservicessuppliedinthelongrun.P圖4.長期總供給曲線產量自然產量率物價水平0長期總供給P21.物價水平變動…2...并不影響長期中物品與勞務的供給量PTheLong-RunAggregate-SupplyCurve長期總供給曲線Thelong-runaggregate-supplycurveisverticalatthenaturalrateofoutput.長期總供給曲線是在自然產量率時的一條垂線。Thislevelofproductionisalsoreferredtoaspotentialoutputorfull-employmentoutput.這一產量水平也被稱為潛在產量或充分就業產量。20.4.2WhytheLong-RunAggregate-SupplyCurveMightShift

為什么長期總供給曲線會移動Anychangeintheeconomythataltersthenaturalrateofoutputshiftsthelong-runaggregate-supplycurve.經濟中任何改變自然產量率的變動都會使長期總供給曲線移動。Theshiftsmaybecategorizedaccordingtothevariousfactorsintheclassicalmodelthataffectoutput.可以根據古典模型中影響產量的各種因素把這些移動進行歸類。Shiftsarisingfrom

移動起因于Labor勞動Capital資本NaturalResources自然資源TechnologicalKnowledge技術知識20.4.3ANewWaytoDepictLong-RunGrowthandInflation

描述長期增長與通貨膨脹的新方法Short-runfluctuationsinoutputandpricelevelshouldbeviewedasdeviationsfromthecontinuinglong-runtrends.

應該把短期產量與物價水平波動作為與持續的長期趨勢的背離。Figure5Long-RunGrowthandInflationQuantityofOutputY1980AD1980AD1990AggregateDemand,AD2000PriceLevel0Long-runaggregatesupply,LRAS1980Y1990LRAS1990Y2000LRAS2000P19801.Inthelongrun,technologicalprogressshiftslong-runaggregatesupply...4....andongoinginflation.3....leadingtogrowthinoutput...P1990P20002....andgrowthinthemoneysupplyshiftsaggregatedemand...圖5.長期增長與通貨膨脹產量Y1980AD1980AD1990總需求AD2000物價水平0長期總供給LRAS1980Y1990LRAS1990Y2000LRAS2000P19801.在長期中，技術進步使長期總供給移動….4.....及持續的通貨膨脹.3.....引起產量增長….P1990P20002.....以及貨幣供給增長使總需求移動…20.4.4WhytheAggregate-SupplyCurveSlopesUpwardintheShortRun

為什么短期中總供給曲線向右上方傾斜Intheshortrun,anincreaseintheoveralllevelofpricesintheeconomytendstoraisethequantityofgoodsandservicessupplied.在短期中,經濟中物價總水平的上升傾向于增加物品與勞務的供給量。Adecreaseinthelevelofpricestendstoreducethequantityofgoodsandservicessupplied.物價總水平的下降傾向于減少物品與勞務的供給量。Figure6TheShort-RunAggregate-SupplyCurveQuantityofOutputPriceLevel0Short-runaggregatesupply1.Adecreaseinthepricelevel...2....reducesthequantityofgoodsandservicessuppliedintheshortrun.YPY2P2圖6.短期總供給曲線產量物價水平0短期總供給1.物價水平下降….減少了短期中物品與勞務的供給量。YPY2P2Why

theAggregate-SupplyCurveSlopesUpwardintheShortRun

為什么短期中總供給曲線向右上方傾斜TheMisperceptionsTheory

錯覺理論TheSticky-WageTheory粘性工資理論TheSticky-PriceTheory粘性價格理論（1）TheMisperceptionsTheoryChangesintheoverallpriceleveltemporarilymisleadsuppliersaboutwhatishappeninginthemarketsinwhichtheyselltheiroutput:Alowerpricelevelcausesmisperceptionsaboutrelativeprices.Thesemisperceptionsinducesupplierstodecreasethequantityofgoodsandservicessupplied.

（1）錯覺理論物價總水平的變動會暫時誤導供給者對他們出售其產品的市場發生的變動的看法:低物價水平引起對相對價格的錯覺。這些錯覺引起供給者減少物品與勞務的供給量。（2）TheSticky-WageTheoryNominalwagesareslowtoadjust,orare“sticky”intheshortrun:Wagesdonotadjustimmediatelytoafallinthepricelevel.Alowerpricelevelmakesemploymentandproductionlessprofitable.Thisinducesfirmstoreducethequantityofgoodsandservicessupplied.（2）粘性工資理論名義工資調整緩慢，或者說在短期中是“粘性的”:工資不能根據物價水平迅速調整。較低的物價水平使就業和生產不利。這就引起企業減少物品與勞務的供給量。（3）TheSticky-PriceTheory

Pricesofsomegoodsandservicesadjustsluggishlyinresponsetochangingeconomicconditions:Anunexpectedfallinthepricelevelleavessomefirmswithhigher-than-desiredprices.Thisdepressessales,whichinducesfirmstoreducethequantityofgoodsandservicestheyproduce.（3）粘性價格理論

一些物品與勞務的價格對經濟狀況變動的調整也是緩慢的:未預期到的物價水平下降使一些企業的價格高于合意水平。這就抑制了銷售，并引起企業減少它們生產的物品與勞務量。20.4.5WhytheShort-RunAggregate-SupplyCurveMightShift

為什么短期總供給曲線會移動Shiftsarisingfrom

移動起因于Labor勞動Capital資本NaturalResources.自然資源Technology.技術ExpectedPriceLevel.預期物價水平Anincreaseintheexpectedpricelevelreducesthequantityofgoodsandservicessuppliedandshiftstheshort-runaggregatesupplycurvetotheleft.預期物價水平上升減少了物品與勞務供給量，并使短期總供給曲線向左移動。Adecreaseintheexpectedpricelevelraisesthequantityofgoodsandservicessuppliedandshiftstheshort-runaggregatesupplycurvetotheright.預期物價水平下降增加了物品與勞務供給量，并使短期總供給曲線向右移動。Figure7TheLong-RunEquilibriumNaturalrateofoutputQuantityofOutputPriceLevel0Short-runaggregatesupplyLong-runaggregatesupplyAggregatedemandAEquilibriumprice圖7.長期均衡自然產量率產量物價水平0短期總供給長期總供給總需求A均衡價格20.5TWOCAUSESOFECONOMICFLUCTUATIONS（1）ShiftsinAggregateDemandIntheshortrun,shiftsinaggregatedemandcausefluctuationsintheeconomy’soutputofgoodsandservices.Inthelongrun,shiftsinaggregatedemandaffecttheoverallpricelevelbutdonotaffectoutput.20.5經濟波動的兩個原因（1）總需求移動在短期中，總需求移動引起經濟中物品與勞務產量的波動。在長期中，總需求移動影響物價總水平，但不影響產量。Figure8AContractioninAggregateDemandQuantityofOutputPriceLevel0Short-runaggregatesupply,ASLong-runaggregatesupplyAggregatedemand,ADAPYAD2AS21.Adecreaseinaggregatedemand...2....causesoutputtofallintheshortrun...3....butovertime,theshort-runaggregate-supplycurveshifts...4....andoutputreturnstoitsnaturalrate.CP3BP2Y2圖8.總需求減少產量物價水平0短期總供給,AS1長期總供給總需求,ADAPYAD2AS21.總需求減少…..2....引起短期中產量減少

...3……但隨著時間推移，短期總供給曲線移動……4……產量恢復到其自然產量率水平。CP3BP2Y2畫出美國經濟的AD-SRAS-LRAS圖形，從經濟的長期均衡開始加拿大出現經濟繁榮，用你的圖形分析這對美國GDP，物價水平和失業率的短期與長期影響課堂練習

2

模型的應用68課堂練習

2

參考答案69LRASYNPYAD2SRAS2AD1SRAS1P1P3CP2Y2BA事件：加拿大經濟繁榮1.影響

NX，AD曲線2. AD曲線向右移動3. 短期均衡在點B。P與Y

增加，失業率降低4. 隨時間的推移，PE上升，SRAS曲線一直向左移動，直到達到長期均衡點C。Y與失業率回到起始水平0（2）AnAdverseShiftinAggregateSupplyAdecreaseinoneofthedeterminantsofaggregatesupplyshiftsthecurvetotheleft:Outputfallsbelowthenaturalrateofemployment.Unemploymentrises.Thepricelevelrises.（2）總供給的不利移動總供給決定因素中任何一種降低都使總供給曲線向左移動:產量下降到自然就業率水平以下。失業率上升。物價水平上漲。Figure10An

AdverseShiftinAggregateSupplyQuantityofOutputPriceLevel0Aggregatedemand3....andthepriceleveltorise.2....causesoutputtofall...1.Anadverseshiftintheshort-runaggregate-supplycurve...Short-runaggregatesupply,ASLong-runaggregatesupplyYAPAS2BY2P2圖10.總供給的不利移動產量物價水平0總需求3....以及物價水平上升。2....引起產量減少...1.短期總供給曲線的不利移動……短期總供給AS長期總供給YAPAS2BY2P2TheEffectsofaShiftinAggregateSupply（1）StagflationAdverseshiftsinaggregatesupplycausestagflation—aperiodofrecessionandinflation.Outputfallsandpricesrise.Policymakerswhocaninfluenceaggregatedemandcannotoffsetbothoftheseadverseeffectssimultaneously.總供給移動的影響（1）滯脹總供給的不利移動會引起滯脹—衰退和通貨膨脹并存的時期。產量減少而物價上升。那些能影響總需求的決策者不能同時抵消這兩種不利的影響。（2）PolicyResponsestoRecessionPolicymakersmayrespondtoarecessioninoneofthefollowingways:Donothingandwaitforpricesandwagestoadjust.Takeactiontoincreaseaggregatedemandbyusingmonetaryandfiscalpolicy.總供給移動的影響（2）對付衰退的政策政策制定者可以用下列手段之一來對付衰退:什么也不做，等待價格和工資調整。利用貨幣和財政政策增加總需求。Figure11AccommodatinganAdverseShiftinAggregateSupplyQuantityofOutputNaturalrateofoutputPriceLevel0Short-runaggregatesupply,ASLong-runaggregatesupplyAggregatedemand,ADP2APAS23....whichcausesthepriceleveltorisefurther...4....butkeepsoutputatitsnaturalrate.2....policymakerscanaccommodatetheshiftbyexpandingaggregatedemand...1.Whenshort-runaggregatesupplyfalls...AD2CP3圖11.抵消總供給的不利移動產量自然產量率物價水平0短期總供給AS長期總供給總需求,ADP2APAS23....這引起物價水平進一步上升……4....但產量保持在自然產量率水平2....決策者可以通過擴大總需求來抵消這種移動……1.當短期總供給減少時…AD2CP3SummaryAllsocietiesexperienceshort-runeconomicfluctuationsaroundlong-runtrends.Thesefluctuationsareirregularandlargelyunpredictable.Whenrecessionsoccur,re