CHAPTER 35曼昆经济学.docx

CHAPTER 35曼昆经济学.docx

《CHAPTER 35曼昆经济学.docx》由会员分享，可在线阅读，更多相关《CHAPTER 35曼昆经济学.docx（12页珍藏版）》请在冰点文库上搜索。

CHAPTER35曼昆经济学

CHAPTER35THESHORT-RUNTRADEOFFBETWEENINFLATIONANDUNEMPLOYMENT

LEARNINGOBJECTIVES:

Øwhypolicymakersfaceashort-runtradeoffbetweeninflationandunemployment.

Øwhytheinflation-unemploymenttradeoffdisappearsinthelongrun.

Øhowsupplyshockscanshifttheinflation-unemploymenttradeoff.

Øtheshort-runcostofreducinginflation.

Øhowpolicymakers’credibilitymightaffectthecostofreducinginflation.

KEYPOINTS:

1.ThePhillipscurvedescribesanegativerelationshipbetweeninflationandunemployment.Byexpandingaggregatedemand,policymakerscanchooseapointonthePhillipscurvewithhigherinflationandlowerunemployment.Bycontractingaggregatedemand,policymakerscanchooseapointonthePhillipscurvewithlowerinflationandhigherunemployment.

2.ThetradeoffbetweeninflationandunemploymentdescribedbythePhillipscurveholdsonlyintheshortrun.Inthelongrun,expectedinflationadjuststochangesinactualinflation,andtheshort-runPhillipscurveshifts.Asaresult,thelong-runPhillipscurveisverticalatthenaturalrateofunemployment.

3.Theshort-runPhillipscurvealsoshiftsbecauseofshockstoaggregatesupply.Anadversesupplyshock,suchastheincreaseinworldoilpricesduringthe1970s,givespolicymakersalessfavorabletradeoffbetweeninflationandunemployment.Thatis,afteranadversesupplyshock,policymakershavetoacceptahigherrateofinflationforanygivenrateofunemployment,orahigherrateofunemploymentforanygivenrateofinflation.

4.WhentheFedcontractsgrowthinthemoneysupplytoreduceinflation,itmovestheeconomyalongtheshort-runPhillipscurve,whichresultsintemporarilyhighunemployment.Thecostofdisinflationdependsonhowquicklyexpectationsofinflationfall.Someeconomistsarguethatacrediblecommitmenttolowinflationcanreducethecostofdisinflationbyinducingaquickadjustmentofexpectations.

OUTLINE:

I.ThePhillipsCurve

A.OriginsofthePhillipsCurve

1.In1958,aneconomistnamedA.W.PhillipspublishedanarticlediscussingthenegativecorrelationbetweeninflationratesandunemploymentratesintheUnitedKingdom.

2.AmericaneconomistsPaulSamuelsonandRobertSolowshowedasimilarrelationshipbetweeninflationandunemploymentfortheUnitedStatestwoyearslater.

3.Thebeliefwasthatlowunemploymentisrelatedtohighaggregatedemand,andhighaggregatedemandputsupwardpressureonprices.Likewise,highunemploymentisrelatedtolowaggregatedemand,andlowaggregatedemandpullspricelevelsdown.

4.DefinitionofPhillipscurve:

acurvethatshowstheshort-runtradeoffbetweeninflationandunemployment.

Figure1

5.SamuelsonandSolowbelievedthatthePhillipscurveofferedpolicymakersamenuofpossibleeconomicoutcomes.Policymakerscouldusemonetaryandfiscalpolicytochooseanypointonthecurve.

B.AggregateDemand,AggregateSupply,andthePhillipsCurve

Figure2

1.ThePhillipscurveshowsthecombinationsofinflationandunemploymentthatariseintheshortrunduetoshiftsintheaggregatedemandcurve.

2.Thegreatertheaggregatedemandforgoodsandservices,thegreatertheeconomy’soutputandthehigherthepricelevel.Greateroutputmeanslowerunemployment.Whateverthepreviousyear’spricelevelhappenstobe,thehigherthepricelevelinthecurrentyear,thehighertherateofinflation.

3.Example:

Thepricelevelis100（measuredbytheConsumerPriceIndex）intheyear2000.Therearetwopossiblechangesintheeconomyfortheyear2001:

alowlevelofaggregatedemandorahighlevelofaggregatedemand.

a.Iftheeconomyexperiencesalowlevelofaggregatedemand,wewouldbeatashort-runequilibriumlikepointA.ThispointalsocorrespondswithpointAonthePhillipscurve.Notethatwhenaggregatedemandislow,theinflationrateisrelativelylowandtheunemploymentrateisrelativelyhigh.

b.Iftheeconomyexperiencesahighlevelofaggregatedemand,wewouldbeatashort-runequilibriumlikepointB.ThispointalsocorrespondswithpointBonthePhillipscurve.Notethatwhenaggregatedemandishigh,theinflationrateisrelativelyhighandtheunemploymentrateisrelativelylow.

4.Giventhatmonetaryandfiscalpolicycanbothshifttheaggregate-demandcurve,thesetypesofpoliciescanmovetheeconomyalongthePhillipscurve.

a.Increasesinthemoneysupply,increasesingovernmentspending,ordecreasesintaxesallincreaseaggregatedemandandmovetheeconomytoapointonthePhillipscurvewithlowerunemploymentandhigherinflation.

b.Decreasesinthemoneysupply,decreasesingovernmentspending,orincreasesintaxesallloweraggregatedemandandmovetheeconomytoapointonthePhillipscurvewithhigherunemploymentandlowerinflation.

II.ShiftsinthePhillipsCurve:

TheRoleofExpectations

A.TheLong-RunPhillipsCurve

Figure3

1.In1968,economistMiltonFriedmanarguedthatmonetarypolicyisonlyabletochooseacombinationofunemploymentandinflationforashortperiodoftime.Atthesametime,economistEdmundPhelpswroteapapersuggestingthesamething.

2.Thisistruebecause,inthelongrun,monetarygrowthhasnorealeffects.Thismeansthatitcannotaffectthefactorsthatdeterminetheeconomy’sunemploymentrate.

3.Thus,inthelongrun,wewouldnotexpecttheretobearelationshipbetweenunemploymentandinflation.Thismustmeanthat,inthelongrun,thePhillipscurveisvertical.

Figure4

4.TheverticalPhillipscurveoccursbecause,inthelongrun,theaggregatesupplycurveisverticalaswell.Thus,increasesinaggregatedemandleadonlytochangesinthepricelevelandhavenoeffectontheeconomy’slevelofoutput.Thus,inthelongrun,unemploymentwillnotchangewhenaggregatedemandchanges,butinflationwill.

5.Thelong-runaggregate-supplycurveoccursattheeconomy’snaturalrateofoutput;thus,thelong-runPhillipscurveoccursatthenaturalrateofunemployment.

B.ExpectationsandtheShort-RunPhillipsCurve

1.Theshort-runaggregatesupplycurveisupwardslopingbecauseofmisperceptionsaboutrelativeprices,stickywages,andstickyprices.Theseperceptions,wages,andpricesadjustovertime,sothatthepositiverelationshipbetweenthepricelevelandthequantityofgoodsandservicessuppliedoccursonlyintheshortrun.

2.ThissamelogicappliestothePhillipscurve.Thetradeoffbetweeninflationandunemploymentholdsonlyintheshortrun.

3.Theexpectedlevelofinflationisanimportantfactorinunderstandingthedifferencebetweenthelong-runandtheshort-runPhillipscurves.Expectedinflationmeasureshowmuchpeopleexpecttheoverallpriceleveltochange.

4.Theexpectedrateofinflationisonevariablethatdeterminesthepositionoftheshort-runaggregate-supplycurve.Thisistruebecausetheexpectedpricelevelaffectstheperceptionsofrelativepricesthatpeopleformandthewagesandpricesthattheyset.

5.Intheshort-run,people’sexpectationsaresomewhatfixed.Thus,whentheFedincreasesthemoneysupply,aggregatedemandincreasesalongtheupwardslopingshort-runaggregate-supplycurve.Outputgrows（unemploymentfalls）andthepricelevelrises（inflationincreases）.

6.Eventually,however,peoplewillrespondbychangingtheirexpectationsofthepricelevel.Specifically,theywillbeginexpectingahigherrateofinflation.

7.Wecanrelatetheactualunemploymentratetothenaturalrateofunemployment,theactualinflationrate,andtheexpectedinflationrateusingthefollowingequation:

a.Becauseexpectedinflationisalreadygivenintheshortrun,higheractualinflationleadstolowerunemployment.

b.Howmuchunemploymentchangesinresponsetoachangeininflationisdeterminedbythevariable,whichisrelatedtotheslopeoftheshort-runaggregate-supplycurve.

Figure5

8.Ifpolicymakerswanttotakeadvantageoftheshort-runtradeoffbetweenunemploymentandinflation,itmayleadtonegativeconsequences.

a.SupposetheeconomyisatpointAandpolicymakerswishtolowertheunemploymentrate.Expansionarymonetarypolicyorfiscalpolicyisusedtoshiftaggregatedemandtotheright.TheeconomymovestopointB,withalowerunemploymentrateandahigherrateofinflation.

b.Overtime,peoplegetusedtothisnewlevelofinflationandraisetheirexpectationsofinflation.Thisleadstoanupwardshiftoftheshort-runPhillipscurve.TheeconomyendsupatpointC,withahigherinflationratethanatpointA,butthesamelevelofunemployment.

C.TheNaturalExperimentfortheNatural-RateHypothesis

1.Definitionofthenatural-ratehypothesis:

theclaimthatunemploymenteventuallyreturnstoitsnormal,ornaturalrate,regardlessoftherateofinflation.

Figure6

2.Figure6showstheunemploymentrateandinflationratefrom1961to1968.Itiseasytoseetheinverserelationshipbetweenthesetwovariables.

3.Beginninginthelate1960s,thegovernmentfollowedpoliciesthatincreasedaggregatedemand.

a.GovernmentspendingrosebecauseoftheVietnamWar.

b.TheFedincreasedthemoneysupplytotrytokeepinterestratesdown.

4.Asaresultofthesepolicies,theinflationrateremainedfairlyhigh.However,eventhoughinflationremainedhigh,unemploymentdidnotremainlow.

Figure7

a.Figure7showstheinflationrateandtheunemploymentratefrom1961to1973.Thesimpleinverserelationshipbetweenthesetwovariablesbegantodisappearin1970.

b.Thisoccurredbecausepeople’sinflationexpectationsadjustedtothehigherrateofinflationandtheunemploymentratereturnedtoitsnaturalrateofaround5to6percent.

III.ShiftsinthePhillipsCurve:

TheRoleofSupplyShocks