布兰查得 宏观经济 第九章

Output,Unemployment,

andInflationThischaptercharacterizestheeconomybythreerelations:Okun’sLaw,whichrelatesthechangeinunemploymenttooutputgrowth.ThePhillipscurve,whichrelatesthechangesininflationtounemployment.Theaggregatedemandrelation,whichrelatesoutputgrowthtobothnominalmoneygrowthandinflation.9-12Okun’sLawAccordingtotheequationabove,thechangeintheunemploymentrateshouldbeequaltothenegativeofthegrowthrateofoutput.Forexample,ifoutputgrowthis4%,thentheunemploymentrateshoulddeclineby4%.Note:

Thisequationisderivedfromfollowingtwoconvenientbutrestrictiveassumption:Outputmovedoneforonewithemployment,ie.Y=N;Laborforcewasconstant,sochangesinemploymentwasreflectedoneforoneinoppositechangesinunemployment.3Okun’sLawTheactualrelationbetweenoutputgrowthandthechangeintheunemploymentrateisknownasOkun’slaw.Usingthirtyyearsofdataintheunitedstates,therelationthatbestfitsthedataisgivenby:4

Thisequationdiffersfrompriorequationintwoways:A.Itconsidersfactorssuchaslaborforcegrowthandlaborproductivitygrowth,3%.Itimpliesthatjusttomaintainaconstantunemploymentrate,outputgrowthmustbeequaltothesumoflaborforcegrowthandlaborproductivitygrowth.5Okun’sLawHighoutputgrowthisassociatedwithareductionintheunemploymentrate;lowoutputgrowthisassociatedwithanincreaseintheunemploymentrate.ChangesintheUnemploymentRateVersusOutputGrowthintheUnitedStatessince1970Figure9-16Okun’sLawAccordingtotheequationabove,Tomaintaintheunemploymentrateconstant,outputgrowthmustbe3%peryear.Thisgrowthrateofoutputiscalledthenormalgrowthrate.7Okun’sLawB.Thecoefficientontherightis-0.4rather-0.1.Accordingtotheequationabove,outputgrowth1%abovenormalleadsonlytoa0.4%reductioninunemployment,fortworeasons:Laborhoarding:firmsadjustemploymentlessthanoneforoneinresponseofoutputgrowthfromnormal.Firmsprefertokeepworkersratherthanlaythemoffwhenoutputdecreases.Anincreaseintheunemploymentratedoesnotleadtoaoneforonedecreaseintheemploymentrate.Whenemploymentincreases,notallnewjobsarefilledbytheunemployed,alsobyoutofthelaborforce.A0.6%increaseintheemploymentrateleadstoonlya0.4%decreaseintheunemploymentrate.8Okun’sLawUsinglettersratherthannumbers:Outputgrowthabove(below)normalleadstoadecrease(increase)intheunemploymentrate.ThisisOkun’slaw:9Okun’sLawAcrossCountriesTable1Okun’sLawCoefficientsAcrossCountriesandTimeCountry1960-1980β1981-2023βUnitedStates0.390.39UnitedKingdom0.150.54Germany0.200.32Japan0.020.12ThecoefficientβinOkun’slawgivestheeffectontheunemploymentrateofdeviationsofoutputgrowthfromnormal.Avalueofβof0.4tellsusthatoutputgrowth1%abovethenormalgrowthratefor1yeardecreasestheunemploymentrateby0.4%.10ThePhillipsCurveInflationdependsonexpectedinflationandonthedeviationofunemploymentfromthenaturalrateofunemployment.Whenetiswellapproximatedbyt-1,then:AccordingtothePhillipscurve,11TheAggregateDemandRelationTheaggregatedemandrelation,asstatedinchapter7,addingthetimeindices:Tofocusontherelationbetweentherealmoneystockandoutput,hereweignoringchangesinoutputcausedbyotherthanchangesintherealmoneystock,then:12TheAggregateDemandRelationKeepinmindthissimplerelationhidesthemechanismyousawintheIS-LMmodel:Anincreaseintherealmoneystockleadstoadecreaseintheinterestrate.Thedecreaseintheinterestrateleadstoanincreaseinthedemandforgoodsandtherefore,toanincreaseinoutput.13Fromtherelationthataboveequationgives,wecanderiveanotherrelationbetweengrowthrates----thegrowthrateofoutput,gyt,thegrowthratemoney,gmt,andtheinflationrate(thegrowthrateofpricelevel.),πt.

14TheEffectsofMoneyGrowthOkun’slawrelatesthechangeintheunemploymentratetothedeviationofoutputgrowthfromnormal:ThePhillipscurverelatesthechangeininflationtothedeviationoftheunemploymentratefromthenaturalrate:Theaggregatedemandrelationrelatesoutputgrowthtothedifferencebetweennominalmoneygrowthandinflation.9-215TheEffectsofMoneyGrowthFigure9-2OutputGrowth,Unemployment,Inflation,andNominalMoneyGrowth16TheMediumRun

Toseewhatthesethreerelationsimplyfortheeffectsofnominalmoneygrowthonoutput\unemploymentandinflation,theeasiestwaytoproceedistoworkbackwardintime.Thatis,tostartbylookingatmediumrun---wheretheeconomyendupwhenallthedynamicshaveworkedthemselvesout,andthenturntothedynamicsthemselves,i.e.,howtheeconomygetthere.17TheMediumRunAssumethatthecentralbankmaintainsaconstantgrowthrateofnominalmoney,callit.Inthiscase,whatwillbethevaluesofoutputgrowth,unemployment,andinflationinthemediumrun?18Inthemediumrun,theunemploymentratemustbeconstant,ThenaccordingOkun’slaw,theoutputmustgrowatitsnormalrateofgrowth

19Inthemediumrun,accordingtheaggregatedemandrelation,theinflationmustbeequaltonominalmoneygrowthminusnormaloutputgrowth.

Ifwedefineadjustednominalmoneygrowthasequaltonominalmoneygrowthminusnormaloutputgrowth,sointhemediumrun,inflationequalsadjustednominalmoneygrowth.20Ifinflationisconstant---equalsadjustednominalmoneygrowth,accordingtothephillipscurve,theunemploymentratemustequaltothenaturalrateofunemployment.21Let’ssummarize:Inthemediumrun,outputisequaltothenormalgrowthrate;unemploymentisequaltothenaturalrate,bothofthemareindependentofnominalmoneygrowth.Sonominalmoneygrowthaffectsonlyinflation-----changesinthelevelofnominalmoneyareneutralinthemediumrun,whicharereflectedoneforoneinchangesintherateofinflation.

“Inflationisalwaysandeverywhereamonetaryphenomenon.”_Miltonfriedman22TheShortRunLet’snowturntodynamicsbeginningwiththeassumptionthattheeconomyisinitiallyatitsmediumrunequilibrium.Supposethatthecentralbankdecidestodecreasenominalmoneygrowth.Whatwillhappenintheshortrun?First,giventheinitialrateofinflation,thenaccordingtotheADrelation,lowernominalmoneygrowthleadstolowerrealnominalmoneygrowth,andthusleadstoadecreaseinoutputgrowth---belowthenaturalgrowthrate.23Second,accordingtoOkun’slaw,whenoutputgrowthisbelownormalrateleadstoanincreaseinunemployment.Third,accordingtothePhillipscurverelation,whenUnemploymentrateisabovethenaturalrateleadstoadecreaseininflation.Sotightermonetarypolicyleadsinitiallytoarecessionandlowerinflation.

24WorkingOutthePath

ofNominalMoneyGrowthThistableshowsthepathofnominalmoneygrowthneededtoachieve10%disinflationoverfiveyears.Table9-1EngineeringDisinflation012345678Inflation(%)141210864444Unemployment

rate(%)688888666Outputgrowth(%)323333833Nominalmoneygrowth(%)1710131197127725WorkingOutthePath

ofNominalMoneyGrowthThisfigureshowsthepathofunemploymentandinflationimpliedbythedisinflationpathinTable9-1.Fiveyearsofunemploymentabovethenaturalrateofunemploymentleadtoapermanentdecreaseininflation.ADisinflationPath26Disinflation9-3Weknowfromtheprevioussectionthatlowerinflationrequireslowermoneygrowth.Wealsoknowthatlowermoneygrowthimpliesanincreaseinunemploymentforsometime.Nowwediscussatwhatpacethecentralbankshouldproceed.27AFirstPassInthePhillipscurverelationabove,disinflation—adecreaseininflationrate—canbeobtainedonlyatthecostofhigherunemployment.(note:deflation—decreaseinthepricelevel,equivalentnegativeinflation)Apoint-yearofexcessunemploymentisadifferencebetweentheactualandthenaturalunemploymentrateofonepercentagepointforoneyear.28AFirstPassForexample,let’sassumethat=1Supposethecentralbankwantstoachievethereductionininflationin1year,then1yearofunemploymentat10%abovethenaturalrateisrequiredSupposethecentralbankwantstoachievethereductionininflationover2years,then2yearsofunemploymentat5%abovethenaturalrateisrequired.29AFirstPassForexample,let’sassumethat=1Bythesamereasoning,reducinginflationover5yearsrequires5yearsofunemploymentat2%abovethenaturalrate(fivetimes2%=10%);reducinginflationover10yearsrequires10yearofunemploymentat1%abovethenaturalrate.30AFirstPassThesacrificeratioisthenumberofpoint-yearsofexcessunemploymentneededtoachieveadecreaseininflationof1%.Forexample,ifisroughlyequaltoone,astheestimatedPhillipscurvesuggests,thenthesacrificeratioofroughlyequaltoone.31ExpectationsandCredibility:

TheLucasCritiqueTheLucascritiquestatesthatitisunrealistictoassumethatwagesetterswouldnotconsiderchangesinpolicywhenformingtheirexpectations.Ifwagesetterscouldbeconvincedthatinflationwasindeedgoingtobelowerthaninthepast,theywoulddecreasetheirexpectationsofinflation,whichwouldinturnreduceactualinflation,withouttheneedforachangeintheunemploymentrate.32ExpectationsandCredibility:

TheLucasCritiqueThomasSargent,whoworkedwithRobertLucas,arguedthatanyinordertoachievedisinflation,anyincreaseinunemploymentwouldhavetobeonlysmall.Theessentialingredientofsuccessfuldisinflation,heargued,wascredibilityofmonetarypolicy—thebeliefbywagesettersthatthecentralbankwastrulycommittedtoreducinginflation.Thecentralbankshouldaimforfastdisinflation.33NominalRigiditiesandContractsAcontraryviewwastakenbyStanleyFischerandJohnTaylor.Theyemphasizedthepresenceofnominalrigidities,orthefactthatmanywagesandpricesarenotreadjustedwhenthereisachangeinpolicy.Ifwagesaresetbeforethechangeinpolicy,inflationwouldalreadybebuiltintoexistingwageagreements.34NominalRigiditiesandContractsWhileFischerarguedthatevenwithcredibility,toorapidadecreaseinnominalmoneygrowthwouldleadtohigherunemployment,Taylor’sargumentwentonestepfurther.Hearguedthatwagecontractsarenotallsignedatthesametime,butthattheyarestaggeredovertime.Heshowedthatthisstaggeringofwagedecisionsimposedstronglimitsonhowfastdisinflationcouldproceedwithouttriggeringhigherunemployment.35NominalRigiditiesandContractsFigure9-3DisinflationWithoutUnemploymentintheTaylorModelIfwagedecisionsarestaggered,disinflationmustbephasedinslowlytoavoidanincreaseinunemployment.36TheU.S.Disinflation,1970-1985Figure1TheFederalFundsRateandInflation,1979-1984AsharpincreaseinthefederalfundsratefromSeptember1979toApril1980wasfollowedbyasharpdeclineinmid-1980,andthenasecondandsustainedincreasefromJanuary1981on,lastingformostof1981and1982.37Cumulativeunemploymentisthesumofpoint-yearsofexcessunemploymentfrom1