宏观经济学（第十三版）课件：Aggregate Supply and Demand

AggregateSupplyandDemand

.IntroductionThelastfewchaptershavedetailedmodelsoflongruneconomicgrowthnowturntoshortrunfluctuationsintheeconomythatconstitutethebusinesscycleTheAS/ADmodelisthebasicmacroeconomictoolforstudyingoutputfluctuationsandthedeterminationofthepricelevelandtheinflationrateCanbeusedtoexplainhowtheeconomydeviatesfromapathofsmoothgrowthovertime,andtoexploretheconsequencesofgovernmentpoliciesintendedtoreduceunemploymentandoutputfluctuations,andmaintainstableprices5-2ASandADAggregatesupplycurvedescribes,foreachgivenpricelevel,thequantityofoutputfirmsarewillingtosupplyUpwardslopingsincefirmsarewillingtosupplymoreoutputathigherpricesAggregatedemandcurveshowsthecombinationsofthepricelevelandthelevelofoutputatwhichthegoodsandmoneymarketsaresimultaneouslyinequilibriumDownwardslopingsincehigherpricesreducethevalueofthemoneysupply,whichreducesthedemandforoutputIntersectionofASandADcurvesdeterminestheequilibriumlevelofoutputandpricelevel5-3AS,AD,andEquilibrium

5-4ASandADintersectatpointEinFigure5-1

Equilibrium:AS=ADEquilibriumoutputisY0

ObservedlevelofoutputintheeconomyatparticularpointintimeEquilibriumpricelevelisP0ObservedpricelevelintheeconomyatparticularpointintimeAS,AD,andEquilibrium

5-5ShiftsineithertheASorADscheduleresultinachangeintheequilibriumlevelofpricesandoutputIncreaseinADincreaseinPandYDecreaseinADdecreaseinPandYIncreaseinASdecreaseinPandincreaseinYDecreaseinASincreaseinPanddecreaseinYFigure5-2illustratesanincreaseinADresultingfromanincreaseinmoneysupplyAS,AD,andEquilibrium

5-6

Theamountoftheincrease/decreaseinPandYafterashiftineitheraggregatesupplyoraggregatedemanddependson:TheslopeoftheAScurveTheslopeoftheADcurveTheextentoftheshiftofAS/ADFigure5-3showstheresultofanadverseASshock:ASY,PClassicalSupplyCurveTheclassicalsupplycurveisvertical,indicatingthatthesameamountofgoodswillbesupplied,regardlessofprice[Figure5-4(b)]BasedupontheassumptionthatthelabormarketisinequilibriumwithfullemploymentofthelaborforceThelevelofoutputcorrespondingtofullemploymentofthelaborforce=potentialGDP,Y*5-7ClassicalSupplyCurveY*growsovertimeastheeconomyaccumulatesresourcesandtechnologyimprovesAScurvemovestotherightThegrowththeorymodelsdescribedinearlierchaptersexplainthelevelofY*inaparticularperiodY*is“exogenouswithrespecttothepricelevel”

illustratedasaverticalline,sincegraphedintermsofthepricelevel5-8KeynesianSupplyCurveTheKeynesiansupplycurveishorizontal,indicatingfirmswillsupplywhateveramountofgoodsisdemandedattheexistingpricelevel[Figure5-4(a)]Sinceunemploymentexists,firmscanobtainanyamountoflaboratthegoingwagerateSinceaveragecostofproductiondoesnotchangeasoutputchanges,firmswillingtosupplyasmuchasisdemandedattheexistingpricelevel5-9KeynesianSupplyCurveIntellectualgenesisoftheKeynesianAScurveisfoundintheGreatDepression,whenitseemedfirmscouldincreaseproductionwithoutincreasingPbyputtingidleKandNtoworkAdditionally,pricesareviewedas“sticky”intheshortrun

firmsreluctanttochangepricesandwageswhendemandshiftsInsteadfirmsincrease/decreaseoutputinresponsetodemandshift

flatAScurveintheshortrun

5-10FrictionalUnemploymentandtheNaturalRateofUnemploymentTakenliterally,theclassicalmodelimpliesthatthereisnoinvoluntaryunemploymenteveryonewhowantstoworkisemployedInrealitythereissomeunemploymentduetofrictionsinthelabormarket(Ex.Someoneisalwaysmovingandlookingforanewjob)TheunemploymentrateassociatedwiththefullemploymentlevelofoutputisthenaturalrateofunemploymentNaturalrateofunemploymentistherateofunemploymentarisingfromnormallabormarketfrictionsthatexistwhenthelabormarketisinequilibrium5-11ASandthePriceAdjustmentMechanismAScurvedescribesthepriceadjustmentmechanismwithintheeconomyFigure5-6showstheSRAScurveinblackandtheLRASinblue,andtheadjustmentfromtheSRtotheLRTheAScurveisdefinedbytheequation:(1)wherePt-1isthepricelevelnextperiodPtisthepriceleveltodayY*ispotentialoutput5-12ASandthePriceAdjustmentMechanism

(1)

Ifoutputisabovepotential(Y>Y*),pricesincrease,highernextperiodIfoutputisbelowpotential(Y<Y*),pricesfall,lowernextperiodPricescontinuetorise/fallovertimeuntilY=Y*Today’spriceequalstomorrow’sifoutputequalspotential(ignoringpriceexpectations)ThedifferencebetweenGDPandpotentialGDP,Y-Y*,iscalledtheoutputgap5-13ASandthePriceAdjustmentMechanism

(1)UpwardshiftinghorizontallinesinFigure5-6(b)correspondtosuccessivesnapshotsofequation(1)Beginningwiththehorizontalblacklineattimet=0,atY>Y*,pricehigher(ASshiftingup)byt=1ProcesscontinuesuntilY=Y*

5-14ASandthePriceAdjustmentMechanism

(1)Speedofthepriceadjustmentmechanismcontrolledbytheparameter

Ifislarge,ASmovesquickly(thecounterclock-wiserotationsinFigure5-6(a))Ifissmall,pricesadjustslowlyisofimportancetopolicymakers:Ifislarge,theASmechanismwillreturntheeconomytoY*relativelyquicklyIfissmall,mightwanttouseADpolicytospeeduptheadjustmentprocess5-15ADCurveandShiftsinAD

5-16ADshowsthecombinationofthepricelevelandlevelofoutputatwhichthegoodsandmoneymarketsaresimultaneouslyinequilibriumShiftsinADdueto:Policymeasures(changesinG,T,andMS)ConsumerandinvestorconfidenceFigure5-8showsanoutwardshiftinADresultingfromanincreaseinthemoneysupplyADRelationshipBetween

OutputandPricesKeytotheADrelationshipbetweenoutputandpricesisthedependencyofADonrealmoneysupplyRealmoneysupply=valueofmoneyprovidedbythecentralbankandthebankingsystemRealmoneysupplyiswrittenas,whereisthenominalmoneysupply,andPisthepricelevelAND

Foragivenlevelof,highpricesresultinlowORhighpricesmeanthatthevalueofthenumberofavailabledollarsislowandthusahighP=lowlevelofAD

5-17ADandtheMoneyMarketForthemoment,ignorethegoodsmarketandfocusonthemoneymarketandthedeterminationofADThequantitytheoryofmoneyoffersasimpleexplanationofthelinkbetweenthemoneymarketandADThetotalnumberofdollarsspentinayear,NGDP,isP*YThetotalnumberoftimestheaveragedollarchangeshandsinayearisthevelocityofmoney,VThecentralbankprovidesMdollarsThefundamentalequationunderlyingthequantitytheoryofmoneyisthequantityequation:(2)5-18ADandtheMoneyMarket

(2)Ifthevelocityofmoneyisassumedconstant,equation(2)becomes,andisanequationfortheADcurveForagivenlevelofM,anincreaseinYmustbeoffsetbyadecreaseinP,andviceversaInverserelationshipbetweenYandPasillustratedbydownwardslopingADcurveAnincreaseinMshiftstheADcurveupwardforanyvalueofY5-19ChangesintheMoneyStockandAD

5-20AnincreaseinthenominalmoneystockshiftstheADscheduleupinproportiontotheincreaseinnominalmoneySupposecorrespondstoADandtheeconomyisoperatingatP0andY0Ifmoneystockincreasesby10%to,ADshiftstoAD’

thevalueofPcorrespondingtoY0mustbeP’=1.1P0Thereforereal moneybalancesandYareunchangedADPolicy&theKeynesianSupplyCurve

5-21Figure5-9showstheADscheduleandtheKeynesiansupplyscheduleInitialequilibriumisatpointE(AS=AD)SupposeanaggregatedemandpolicyincreasesADtoAD’Thenewequilibriumpoint,E’,correspondstothesamepricelevel,andahigherlevelofoutput(employmentisalsolikelytoincrease)

ADPolicy&theClassicalSupplyCurve

5-22Intheclassicalcase,ASscheduleisverticalatFElevelofoutputUnliketheKeynesiancase,thepricelevelisnotgiven,butdependsupontheinteractionbetweenASandADSupposeADincreasestoAD’SpendingincreasestoE’BUTfirmscannotobtaintheNrequiredtomeettheincreaseddemandFirmshiremoreworkers&wagesandcostsofproductionrise

firmsmustchargehigherpriceMoveupASandADcurvestoE’’whereAS=AD’ADPolicy&theClassicalSupplyCurve

5-23TheincreaseinpricefromtheincreaseinADreducestherealmoneystock,,and leadstoareductioninspendingTheeconomyonlymovesupADuntilpriceshaverisenenough,andM/Phasfallenenough,toreducetotalspendingtoalevelconsistentwithfullemployment

thisistrueatE’’,whereAD=AS

SupplySideEconomicsSupplysideeconomicsfocusesonASasthedriverintheeconomySupplysidepoliciesarethosethatencouragegrowthinpotentialoutputshiftAStorightSuchpolicymeasuresinclude:RemovingunnecessaryregulationMaintainingefficientlegalsystemEncouragingtechnologicalprogressPoliticiansusethetermsupplysideeconomicsinreferencetotheideathatcuttingtaxeswillincreaseASenoughthattaxcollectionswillactuallyincrease,ratherthanfall5-24SupplySideEconomics

5-25CuttingtaxrateshasanimpactonbothASandADADshiftstoAD’duetoincreaseindisposableincomeShiftisrelativelylargecomparedtothatoftheASASshiftstoAS’astheincentiveto