宏觀經(jīng)濟學（第十三版）課件：Advanced Topics

AdvancedTopics

.IntroductionThischapteroffersadvancedmaterialpresentingtherevolutioninmacroeconomicsthathasdevelopedoverthelast30yearsLookatfivetheoriesinthischapter:RationalexpectationsTherandomwalkofGDPRealbusinesscycletheoryNewKeynesianmodelsofpricestickinessDynamicstochasticgeneralequilibriummodels24-2RationalExpectationsEquilibriumModelsInarationalexpectationsequilibriummodel,marketsclearandthereisnothingsystematicthatmonetarypolicycandotoaffectoutputorunemploymentTheterm“rationalexpectationsequilibrium”identifiestwokeyfeaturesofthisapproachItplacesweightontheroleofexpectations(rationalones)Economicagentsdonotknowthefuturewithcertaintybasetheirplans/decisionsontheirforecastsorexpectationsaboutthefutureIfagentsarerational,theywilluseallavailableinformationwhenformingthoseexpectationsTherationalexpectationsmodelinsistsonequilibriumMarketsclearimmediately24-3RationalExpectations

EquilibriumModelsThefullneoclassicaltheoryofASassertsthat:UnemploymentisalwaysatthenaturalrateOutputisalwaysatthefull-employmentlevelAnyunemploymentispurelyfrictionalNeithermonetarynorfiscalpolicychangeswillhaveanysystematiceffectonoutputTherationalexpectationsapproachassumesthatpeopleuseallrelevantinformationinformingexpectationsofeconomicvariables24-4RationalExpectations

EquilibriumModelsAssumeasimpleADschedule:(1)AssumeasimpleshortrunAScurve,includingpriceexpectations:(2)TheADandASequationscanbecombinedtosolveforoutput(3)andprices(4)intermsofmandothervariablesRewriteADasp=m+v–y,equatingADandAS,andsolvingfory:

(3)24-5RationalExpectations

EquilibriumModelsAssumeasimpleADschedule:(1)AssumeasimpleshortrunAScurve,includingpriceexpectations:(2)TheADandASequationscanbecombinedtosolveforoutput(3)andprices(4)intermsofmandothervariablesPluggingequation(3)intotherewrittenADschedule,andsolvingforpyields:(4)24-6RationalExpectations

EquilibriumModelsTogether,equations(3)and(4)tellustheequilibriumoutputandpricesinourmodeleconomyIfmoneysupplyrises1percent,outputrisesby1/(1+)percentandpricesriseby/(1+)percentIfm,v,andy*areknown,givenpriceexpectations,predictionsforyandpcanbecalculatedusingequations(3)and(4)OftenthemodelgeneratesvaluesthataredifferentfromexpectationsthestandardAS/ADmodelassumesthateconomicagentsmakepredictionsfortheeconomythatareinconsistentwiththepredictionsthemodelitselfmakesTheLucasCritique24-7ThePerfect-ForesightModelThepreviousmodelcanbealteredtoassumethateconomicagentsarecorrectintheirpredictions,orp=peEconomicdecisionmakersuseequation(4)topredictpricesandcomputepe:(5)Collectingtermscontainingpe,wecanrearrange(5)togivetheperfectforesightforecastandsolutionforthepricelevelandthecorrespondingsolutionforoutput:(6)

(7)24-8ThePerfect-ForesightModelTheperfect-foresightpredictionsinequations(6)and(7)arequitedifferentfromtheoriginalAS/ADpredictionsembodiedinequations(3)and(4)ThelatterassumeexogenouslygivenpriceexpectationsTheformerassumethatpriceexpectationsareformedendogenously,andthatexpectationformationisconsistentwiththepredictionsofthemodelThesedifferenceshaveimplicationsfortheeffectivenessofmonetarypolicyUnderaperfectforesightmodel:A1%increaseinthemoneysupplyleadstoexactlya1%increaseinthepricelevelA1%increaseinthemoneysupplyleadstoNOincreaseinoutput24-9ARationalExpectationsModelArationalexpectationsmodelassumesthat:AgentsmakethebestuseofwhateverinformationisavailabletothemExpectationsareformedinamannerconsistentwiththewaytheeconomyactuallyoperatesSimilartoaperfectforesightmodelinwhichsomeofthekeyvariablesareuncertainSupposebeforemoneysupplyisknown,economicdecisionmakersexpectthemoneysupplytoequalmeIfthemoneysupplyturnsouttobem,thedifferencebetweenagents’expectationsandtheactualmoneysupplyis:24-10ARationalExpectationsModelThemonetarypolicymultiplierwithrespecttoanticipatedmoney,me,iszero,justasintheperfect-foresightmodelThemonetarypolicymultiplierwithrespecttounanticipatedmoney,

m,ispositive,justasintheAS/ADmodelTheequilibriumsolutionsforpriceandoutputare:(11)

(12)24-11ARationalExpectationsModelTheeffectofanincreaseinthemoneysupplyunderrationalexpectationsmustbebrokendownintotwoparts:TheeffectofananticipatedincreaseinthemoneysupplyRationalexpectationspredictsNOeffectonoutputRationalexpectationspredictsanequalchangeinpricesTheeffectofanunanticipatedincreaseinthemoneysupplyRationalexpectationspredictsanincreaseinoutputof1/(1+)Rationalexpectationspredictsanincreaseinpricesof/(1+)24-12ARationalExpectationsModelFigure24-1showsactual,anticipated,andunanticipatedM2growth24-13TheRandomWalkofGDPFluctuationsinoutputcanbetransitoryorpermanentIffluctuationsareprimarilypermanent,changesinADmustbeofrelativelylittleimportance:AccordingtotheAS/ADmodel,theeffectofADshockswearsoffwithtimebecausethelong-runaggregatesupplycurveisverticalIftheeffectofshocksispermanent,theirsourcemustbesomethingotherthanaggregatedemandTheideathatchangesinoutputarepermanentcanbedescribedbysayingthatGDPfollowsarandomwalkHavingwanderedupordown,GDPhasnotendencytoreturntotrendstarkcontrasttoimplicitmodeloftext24-14TheRandomWalkofGDP

24-15NelsonandPlosserchallengedthepredominatingideathat:GDPfluctuatesaboutasmoothtrendlineShockstoADaretheprimarycauseofthetransitoryfluctuationsSuggestedthatthetrendisnotsosmoothandissubjecttolargeandfrequentshocksthathaveapermanenteffectonthelevelofGDPNeedtodetrendthedata:Supposethetrendinycanberepresentedbyaliteraltimetrend:(22)Equation(22)statesthatyrisesbyβineverytimeperiodSubtractinglastperiod’syfromeachsideoftheequationyields:(23)OR(24)Equations(22)and(24)areequivalenttooneanotherTheRandomWalkofGDP24-16TheRandomWalkofGDPAccordingtoequation(25),theeffectofashocklastsoneperiodCanbemadestationarybytakingoutatimetrendtrendstationaryDominatedbytransitoryshocksAccordingtoequation(26),theeffectofashockonthelevelofyispermanentCanbemadestationarybydifferencingdifferencestationaryDominatedbypermanentshocksSupposeweaddanoutputshock,ut,toequation(22):

(25)Alternatively,theshockcouldbeaddedtoequation(24):(26)

24-17TheRandomWalkofGDP

24-18AccordingtotheAS/ADmodel:BusinesscyclescausedbyADfluctuationsrelativelyshort-livedShockstoASmightbepermanentifderivedfrompermanentproductivityimprovementsNelsonandPlossershowedthatGDPincludesbothpermanentandtransitoryshocks,butGDPprocessdominatedbypermanentshocksFigure24-4showstheimportanceofpermanentshocksTheRandomWalkofGDPTheideathatshockswithlong-lastingimpactareimportanttotheeconomyisnowgenerallyacceptedTheinferencethatADisrelativelyunimportantremainscontroversialAnalternativeviewisthatlargeandrelativelypermanentaggregatesupplyshocksoccur,butonlyonrareoccasionsInbetween,ADshocksdominate(PierrePerron)TrendstationarywithbreaksImportanceofaggregatedemandshocksremainsacontroversialarea.24-19RealBusinessCycleTheoryRBCtheoryassertsthat:FluctuationsinoutputandemploymentaretheresultofavarietyofrealshocksthathittheeconomyMarketsadjustrapidlyandremaininequilibriumRBCtheoryisthenaturaloutgrowthofthetheoreticalimplicationof:TherationalexpectationsapproachanticipatedmonetarypolicyhasnorealeffectTheempiricalimplicationoftherandomwalktheoryaggregatedemandshocksarenotanimportantsourceoffluctuations24-20RealBusinessCycleTheoryRBCmustdotwothings:ExplaintheshocksthathittheeconomyExplainthepropagationmechanismsmechanismthroughwhichadisturbanceisspreadthroughtheeconomyWhydoshockstotheeconomyseemtohavelong-livedeffects?TheintertemporalsubstitutionofleisureisthepropagationmechanismthatismostassociatedwithequilibriumbusinesscyclesWhydopeopleworkmoreatsometimesthanatothers?DuringboomsemploymentishighandjobsareeasytofindDuringrecessionsemploymentislowerandjobsarehardtofindEmpiricalevidencedoesnotsupporttheexplanationthatpeopleworkmorewhenwagesarehigher24-21RealBusinessCycleTheoryRBCmodelsexplainlargemovementsinoutputwithsmallmovementsinwagesasfollows:ThereisahighelasticityoflaborsupplyinresponsetotemporarychangesinthewagePeoplearewillingtosubstituteleisureintertemporallyPeoplecareabouttheirtotalworkeffectbutcareverylittleaboutwhentheyworkSupposethatwithinatwo-yearperiodtheyplantowork4,000hoursatthegoingwageIfwagesareequalinthetwoyears,theywouldwork2,000eachyearIfwagesare2%higherinoneyearthantheother,theymightwork2,200inthehighwageyear,and1,800intheother24-22RealBusinessCycleTheoryRBCmodelsexplainlargemovementsinoutputwithsmallmovementsinwagesasfollows:ThereisahighelasticityoflaborsupplyinresponsetotemporarychangesinthewageLaborisnotsensitivetopermanentchangesinwagesIfthewagerises,andwillremainhigh,thereisnothinggainedbyworkingmoreinoneyearoveranotherTheintertemporalsubstitutionofleisureisclearlycapableofgeneratinglargemovementsintheamountofworkdoneinresponsetosmallshiftsinwagesCouldaccountforlargeoutputeffectsinthecycleaccompaniedbysmallchangesinwages24-23RealBusinessCycleTheoryThemechanismsthatpropagatebusinesscyclesaresetinmotionbyevents/disturbancesthatchangetheequilibriumlevelsofoutputandemploymentinindividualmarketsandtheeconomyasawholeThemostimportantdisturbancesinRBCtheoryare:Shockstoproductivityorsupplyshocks(Ex.weather,newmethodsofproduction)ShockstogovernmentspendingTheevidencefortheimportanceofmoneyseemspersuasive,makingitdifficultforproponentsoftheRBCtobesuccessfulatconvertingtheprofessiontotheirviews.24-24NewKeynesianModels

ofPriceStickinessThepreviousthreemodelspresentedinthischapterareallintheequilibrium-market-