经济学前沿复习资料

GoldenRulesavingsrateIneconomics,theGoldenRulesavingsrateistherateofsavingswhichmaximizessteadystatelevelorgrowthofconsumption,[1]asforexampleintheSolowgrowthmodel.AlthoughtheconceptcanbefoundearlierinJohnvonNeumannandMauriceAllais'sworks,thetermisgenerallyattributedtoEdmundPhelpswhowrotein1961thattheGoldenRule"dountoothersasyouwouldhavethemdountoyou"couldbeappliedinter-generationallyinsidethemodeltoarriveatsomeformof"optimum",orputsimply"dountofuturegenerationsaswehopepreviousgenerationsdiduntous."[2]IntheSolowgrowthmodel,asteadystatesavingsrateof100%impliesthatallincomeisgoingtoinvestmentcapitalforfutureproduction,implyingasteadystateconsumptionlevelofzero.Asavingsrateof0%impliesthatnonewinvestmentcapitalisbeingcreated,sothatthecapitalstockdepreciateswithoutreplacement.Thismakesasteadystateunsustainableexceptatzerooutput,whichagainimpliesaconsumptionlevelofzero.Somewhereinbetweenisthe"GoldenRule"levelofsavings,wherethesavingspropensityissuchthatper-capitaconsumptionisatitsmaximumpossibleconstantvalue.Putanotherway,thegolden-rulecapitalstockrelatestothehighestlevelofpermanentconsumptionwhichcanbesustained.Inter-temporaltradeoffsNAIRUandrationalexpectationsInthe1970s,newtheories,suchasrationalexpectationsandtheNAIRU(non-acceleratinginflationrateofunemployment)arosetoexplainhowstagflationcouldoccur.Thelattertheory,alsoknownasthe"naturalrateofunemployment",distinguishedbetweenthe"short-term"Phillipscurveandthe"long-term"one.Theshort-termPhillipsCurvelookedlikeanormalPhillipsCurve,butshiftedinthelongrunasexpectationschanged.Inthelongrun,onlyasinglerateofunemployment(theNAIRUor"natural"rate)wasconsistentwithastableinflationrate.Thelong-runPhillipsCurvewasthusvertical,sotherewasnotrade-offbetweeninflationandunemployment.Theexpectations-augmentedPhillipscurveintroducesadaptiveexpectationsintothePhillipscurve.Theseadaptiveexpectations,whichdateformIrvingFisher,sbook“ThePurchasingPowerofMoney”,1911,whereintroducedintothePhillipscurvebymonetarists,speciallyMiltonFriedman.Therefore,wecouldsaythattheexpectations-augmentedPhillipscurvewasfirstusedtoexplainthemonetarists’viewofthePhillipscurve.Adaptiveexpectationsmodelsledtoanimportantshiftintheperceptionofagovernment,sabilitytoact.UnderKeynes,moneyillusion,changesinnominalvariables(prices,wages,etc…)wereacceptedbyagentsasrealdespiteoverallpurchasingpowerremainingstable.However,monetarismembracedtheadaptiveexpectationstheorytomeanthatpeoplewouldstumbleonceortwiceonthesamestone,butnotathird.Inthisway,ifthegovernmentdecidedonanexpansionistmonetarypolicy,inflationwouldriseandunemploymentwouldfall,basedonthePhillipscurve.However,asecondorthirdtimearound,agentswouldbequicktoassociatehigherinflationwithrisingsalariesinaviciouscircle,andadjusttheirbehaviouraccordinglybasedonpastexperiences.Theywouldanticipatethatinflationwoulddraintheirpurchasingpoweraccordingly,andmonetarypolicywouldhavelittleeffect.Ifweseethisgraphically:DynamicinconsistencyIneconomics,dynamicinconsistencyortimeinconsistencydescribesasituationinwhichadecision-maker'spreferenceschangeovertimeinsuchawaythatapreferencecanbecomeinconsistentatanotherpointintime.Thiscanbethoughtofastherebeingmanydifferent"selves"withindecisionmakers,witheach"self"representingthedecision-makeratadifferentpointintime;theinconsistencyoccurswhenallpreferencesarenotaligned.DefinitionTheproblemthatariseswhenadecisionmaker,especiallyapolicymaker,prefersonepolicyinadvancebutadifferentonewhenthetimetoimplementarrives.Knowingthis,otherswillnotfindthecommitmenttothefirstpolicycredible.TheTimeInconsistencyofDiscretionaryPolicyIfweassumethatwecantrustourpolicymakers,discretionatfirstglanceappearssuperiortoafixedpolicyrule.Discretionarypolicyis,byitsnature,flexible.Aslongaspolicymakersareintelligentandbenevolent,theremightappeartobelittlereasontodenythemflexibilityinrespondingtochangingconditions.Yetacaseforrulesoverdiscretionarisesfromtheproblemoftimeinconsistencyofpolicy.Insomesituationspolicymakersmaywanttoannounceinadvancethepolicytheywillfollowtoinfluencetheexpectationsofprivatedecision-makers.Butlater,aftertheprivatedecision-makershaveactedonthebasisoftheirexpectations,thesepolicymakersmaybetemptedtorenegeontheirannouncement.Understandingthatpolicymakersmaybeinconsistentovertime,privatedecision-makersareledtodistrustpolicyannouncements.Inthissituation,tomaketheirannouncementscredible,policymakersmaywanttomakeacommitmenttoafixedpolicyrule.Thesurprisingoutcomeofthisanalysisisthatpolicymakerscansometimesbetterachievetheirgoalsbyhavingtheirdiscretiontakenawayfromthem.Inthecaseofrationalterrorists,fewerhostageswillbetakenandkilledifpolicymakersarecommittedtofollowingtheseeminglyharshruleofrefusingtonegotiateforhostages'freedom.Inthecaseofmonetarypolicy,therewillbelowerinflationwithouthigherunemploymentiftheFediscommittedtoapolicyofzeroinflation.(Thisconclusionaboutmonetarypolicyismodeledmoreexplicitlyintheappendixtothischapter.)RBCtheoryThebusinesscycleoreconomiccycleisthedownwardandupwardmovementofgrossdomesticproduct(GDP)arounditslong-termgrowthtrend.[1]Thesefluctuationstypicallyinvolveshiftsovertimebetweenperiodsofrelativelyrapideconomicgrowth(expansionsorbooms),andperiodsofrelativestagnationordecline(contractionsorrecessions).Realbusiness-cycletheory(RBCtheory)areaclassofNewclassicalmacroeconomicsmodelsinwhichbusiness-cyclefluctuationstoalargeextentcanbeaccountedforbyreal(incontrasttonominal)shocks.Unlikeotherleadingtheoriesofthebusinesscycle,[citationneeded]RBCtheoryseesbusinesscyclefluctuationsastheefficientresponsetoexogenouschangesintherealeconomicenvironment.Thatis,thelevelofnationaloutputnecessarilymaximizesexpectedutility,andgovernmentsshouldthereforeconcentrateonlong-runstructuralpolicychangesandnotintervenethroughdiscretionaryfiscalormonetarypolicydesignedtoactivelysmoothouteconomicshort-termfluctuations.AccordingtoRBCtheory,businesscyclesaretherefore"real"inthattheydonotrepresentafailureofmarketstoclearbutratherreflectthemostefficientpossibleoperationoftheeconomy,giventhestructureoftheeconomy.Mundell-FlemingmodelBasicassumptionsofthemodelareasfollows:Spotandforwardexchangeratesareidentical,andtheexistingexchangeratesareexpectedtopersistindefinitely.Fixedmoneywagerate,unemployedresourcesandconstantreturnstoscaleareassumed.Thusdomesticpriceleveliskeptconstant,andthesupplyofdomesticoutputiselastic.Taxesandsavingincreasewithincome.Thebalanceoftradedependsonlyonincomeandtheexchangerate.Capitalmobilityisperfectandallsecuritiesareperfectsubstitutes.Onlyriskneutralinvestorsareinthesystem.Thedemandformoneythereforedependsonlyonincomeandtheinterestrate,andinvestmentdependsontheinterestrate.Thecountryunderconsiderationissosmallthatthecountrycannotaffectforeignincomesortheworldlevelofinterestrates.UnderaflexibleexchangerateregimeInasystemofflexibleexchangerates,centralbanksallowtheexchangeratetobedeterminedbymarketforcesalone.ChangesinthemoneysupplyAnincreaseinmoneysupplyshiftstheLMcurvetotheright.Thisdirectlyreducesthelocalinterestraterelativetotheglobalinterestrate.Adecreaseinthemoneysupplycausestheexactoppositeprocess.ChangesingovernmentspendingAnincreaseingovernmentexpenditureshiftstheIScurvetotheright.Theshiftcausesboththelocalinterestrateandincome(GDP)torise.Adecreaseingovernmentexpenditurereversestheprocess.ChangesintheglobalinterestrateAnincreaseintheglobalinterestrateshiftstheBoPcurveupwardandcausescapitalflowsoutofthelocaleconomy.Thisdepreciatesthelocalcurrencyandboostsnetexports,shiftingtheIScurvetotheright.Underlessthanperfectcapitalmobility,thedepreciatedexchangerateshiftstheBoPcurvesomewhatbackdown.Underperfectcapitalmobility,theBoPcurveisalwayshorizontalattheleveloftheworldinterestrate.Whenthelattergoesup,theBoPcurveshiftsupwardbythesameamount,andstaysthere.TheexchangeratechangesenoughtoshifttheIScurvetothelocationwhereitcrossesthenewBoPcurveatitsintersectionwiththeunchangedLMcurve;nowthedomesticinterestrateequalsthenewleveloftheglobalinterestrate.Adecreaseintheglobalinterestratecausesthereversetooccur.UnderafixedexchangerateregimeInasystemoffixedexchangerates,centralbanksannounceanexchangerate(theparityrate)atwhichtheyarepreparedtobuyorsellanyamountofdomesticcurrency.Thusnetpaymentsflowsintooroutofthecountryneednotequalzero;theexchangerateeisexogenouslygiven,whilethevariableBoPisendogenous.Underthefixedexchangeratesystem,thecentralbankoperatesintheforeignexchangemarkettomaintainaspecificexchangerate.Ifthereispressuretodepreciatethedomesticcurrency'sexchangeratebecausethesupplyofdomesticcurrencyexceedsitsdemandinforeignexchangemarkets,thelocalauthoritybuysdomesticcurrencywithforeigncurrencytodecreasethedomesticcurrency'ssupplyintheforeignexchangemarket.Thiskeepsthedomesticcurrency'sexchangerateatitstargetedlevel.Ifthereispressuretoappreciatethedomesticcurrency'sexchangeratebecausethecurrency'sdemandexceedsitssupplyintheforeignexchangemarket,thelocalauthoritybuysforeigncurrencywithdomesticcurrencytoincreasethedomesticcurrency'ssupplyintheforeignexchangemarket.Again,thiskeepstheexchangerateatitstargetedlevel.ChangesinthemoneysupplyIntheveryshortrunthemoneysupplyisnormallypredeterminedbythepasthistoryofinternationalpaymentsflows.Ifthecentralbankismaintaininganexchangeratethatisconsistentwithabalanceofpaymentssurplus,overtimemoneywillflowintothecountryandthemoneysupplywillrise(andviceversaforapaymentsdeficit).Ifthecentralbankweretoconductopenmarketoperationsinthedomesticbondmarketinordertooffsetthesebalance-of-payments-inducedchangesinthemoneysupply—aprocesscalledsterilization,itwouldabsorbnewlyarrivedmoneybydecreasingitsholdingsofdomesticbonds(ortheoppositeifmoneywereflowingoutofthecountry).Butunderperfectcapitalmobility,anysuchsterilizationwouldbemetbyfurtheroffsettinginternationalflows.ChangesingovernmentexpenditureAnincreaseingovernmentspendingforcesthemonetaryauthoritytosupplythemarketwithlocalcurrencytokeeptheexchangerateunchanged.Shownhereisthecaseofperfectcapitalmobility,inwhichtheBoPcurve(or,asdenotedhere,theFEcurve)ishorizontal.IncreasedgovernmentexpenditureshiftstheIScurvetotheright.Theshiftresultsinanincipientriseintheinterestrate,andhenceupwardpressureontheexchangerate(valueofthedomesticcurrency)asforeignfundsstarttoflowin,attractedbythehigherinterestrate.However,theexchangerateiscontrolledbythelocalmonetaryauthorityintheframeworkofafixedexchangeratesystem.Tomaintaintheexchangerateandeliminatepressureonit,themonetaryauthoritypurchasesforeigncurrencyusingdomesticfundsinordertoshifttheLMcurvetotheright.Intheend,theinterestratestaysthesamebutthegeneralincomeintheeconomyincreases.IntheIS-LM-BoPgraph,theIScurvehasbeenshiftedexogenouslybythefiscalauthority,andtheISandBoPcurvesdeterminethefinalrestingplaceofthesystem;theLMcurvemerelypassivelyreacts.Thereverseprocessapplieswhengovernmentexpendituredecreases.ChangesintheglobalinterestrateTomaintainthefixedexchangerate,thecentralbankmustaccommodatethecapitalflows(inorout)whicharecausedbyachangeoftheglobalinterestrate,inordertooffsetpressureontheexchangerate.Iftheglobalinterestrateincreases,shiftingtheBoPcurveupward,capitalflowsouttotakeadvantageoftheopportunity.Thisputspressureonthehomecurrencytodepreciate,sothecentralbankmustbuythehomecurrency—thatis,sellsomeofitsforeigncurrencyreserves—toaccommodatethisoutflow.Thedecreaseinthemoneysupplyresultingfromtheoutflow,shiftstheLMcurvetotheleftuntilitintersecttheISandBoPcurvesattheirintersection.Onceagain,theLMcurveplaysapassiverole,andtheoutcomesaredeterminedbytheIS-BoPinteraction.Underperfectcapitalmobility,thenewBoPcurvewillbehorizontalatthenewworldinterestrate,sotheequilibriumdomesticinterestratewillequaltheworldinterestrate.Iftheglobalinterestratedeclinesbelowthedomesticrate,theoppositeoccurs.TheBoPcurveshiftsdown,foreignmoneyflowsinandthehomecurrencyispressuredtoappreciate,sothecentralbankoffsetsthepressurebysellingdomesticcurrency(equivalently,buyingforeigncurrency).TheinflowofmoneycausestheLMcurvetoshifttotheright,andthedomesticinterestratebecomeslower(aslowastheworldinterestrateifthereisperfectcapitalmobility).OptimalCurrencyAreaThegeographicareainwhichasinglecurrencywouldcreatethegreatesteconomicbenefit.Whiletraditionallyeachcountryhasmaintaineditsownseparate,nationalcurrency,workbyRobertMundellinthe1960stheorizedthatthismaynotbethemostefficienteconomicarrangement.Inparticular,countriesthatsharestrongeconomictiesmaybenefitfromacommoncurrency.Thisallowsforcloserintegrationofcapitalmarketsandfacilitatestrade.However,acommoncurrencyresultsinalossofeachcountry'sabilitytodirectfiscalandmonetarypolicyinterventionstostabilizetheireconomies.eacountry’seconomywithintheOCA,asystemwith■businesscyclessothateconomicboomsareshared,andtheOCA’snecessarytothesuccessoftheOCA,butcrucial.Inhis1973“UncommonArgumentsforCommonCurrencies,”Mundellmandatesthatcountriesinsurplusmustmitigatemarketshocksbyclosereconomicandinstitutionalintegrationvia“reservepooling”orrevenuesharing.Thus,afloatingexchangeratethatborderrisksharing.AsGreece’ssovereigndebtcrisiscontinuestoworsenAdverseselection1.Thetendencyofthoseindangerousjobsorhighrisklifestylestogetlifeinsurance.2.Asituationwheresellershaveinformationthatbuyersdon't(orviceversa)aboutsomeaspectofproductquality.SignalingMichaelSpenceoriginallyproposedtheideaofsignaling.Heproposedthatinasituationwithinformationasymmetry,itispossibleforpeopletosignaltheirtype,thusbelievablytransferringinformationtotheotherpartyandresolvingtheasymmetry.Thisideawasoriginallystudiedinthecontextofmatchinginthejobmarket.Anemployerisinterestedinhiringanewemployeewhois"skilledinlearning."Ofcourse,allprospectiveemployeeswillclaimtobe"skilledatlearning",butonlytheyknowiftheyreallyare.Thisisaninformationasymmetry.Skillinlearningismalleable,anddependsuponmanyfactors,includingdiet,exerciseandmoney.Spenceproposes,forexample,thatgoingtocollegecanfunctionasacrediblesignalofanabilitytolearn.Assumingthatpeoplewhoareskilledinlearningcanfinishcollegemoreeasilythanpeoplewhoareunskilled,thenbyfinishingcollegetheskilledpeoplesignaltheirskilltoprospectiveemployers.Nomatterhowmuchorhowlittletheymayhavelearnedincollegeorwhattheystudied,finishingfunctionsasasignaloftheircapacityforlearning.However,finishingcollegemaymerelyfunctionasasignaloftheirabilitytopayforcollege,itmaysignalthewillingnessofindividualstoadheretoorthodoxviews,oritmaysignalawillingnesstocomplywithauthority.ScreeningJosephE.Stiglitzpioneeredthetheoryofscreening.Inthiswaytheunderinformedpartycaninducetheotherpartytorevealtheirinformation.Theycanprovideamenuofchoicesinsuchawaythatthechoicedependsontheprivateinformationoftheotherparty.Examplesofsituationswherethesellerusuallyhasbetterinformationthanthebuyerarenumerousbutincludeused-carsalespeople,mortgagebrokersandloanoriginators,stockbrokersandrealestateagents.Examplesofsituationswherethebuyerusuallyhasbetterinformationthanthesellerincludeestatesalesasspecifiedinalastwillandtestament,lifeinsurance,orsalesofoldartpieceswithoutpriorprofessionalassessmentoftheirvalue.ThissituationwasfirstdescribedbyKennethJ.Arrowinanarticleonhealthcarein1963.[7]GeorgeAkerlofinTheMarketforLemonsnoticesthat,insuchamarket,theaveragevalueofthecommoditytendstogodown,evenforthoseofperfectlygoodquality.Becauseofinformationasymmetry,unscrupuloussellerscan"spoof"items(likereplicagoodssuchaswatches)anddefraudthebuyer.Asaresult,manypeoplenotwillingtoriskgettingrippedoffwillavoidcertaintypesofpurchases,orwillnotspendasmuchforagivenitem.Itisevenpossibleforthemarkettodecaytothepointofnonexistence.MoralHazardTheriskthatapartytoatransactionhasnotenteredintothecontractingoodfaith,hasprovidedmisleadinginformationaboutitsassets,liabilitiesorcreditcapacity,orhasanincentivetotakeunusualrisksinadesperateattempttoearnaprofitbeforethecontractsettles.MechanismdesignWhilehighlyabstractandmathematical,mechanismdesigntheoryhasconcreteapplicationsintherealworld.Itcanprovideimportantjustificationsforgovernmentinterventionintheoperationofmarketssuchashealthcare,aswellashelpingtoconstructrulesthatattempttoavoidthedisparityininformationbetweengroupsofbuyersandsellers.Thatgapinknowledgeisknownineconomicsas"informationasymmetry"andithasbecomeoneofthemostwidelystudiedaspectsofthediscipline.InrecentyearseconomistssuchasGeorgeAkerlofandJosephStiglitzhavebeenawardedNobelprizesfortheirworkinthefield.Becausesellershaveanincentivetoseekthehighestpossiblesaleprice,andbuyershavetheoppositeincentive,andbothpartieshavedifferentlevelsofknowledgeabouttheoverallvalueofthetransaction,thefinaloutcomemaynotefficientfortheeconomyasawhole.Mechanismdesigntheoryattemptstoidentifythesebreakdownsandavoidthemwherepossible.Theinfluenceofmechanismdesigntheorycanbeseeninthestructureofauctions,suchastheUKgovernment'ssaleof3Gmobilephonelicensesin2000,whichnettedtheexchequermorethan£22bninrevenue.Thatwasthankstoaninnovativeproceduredesignedtosqueezepotentialbuyersintomakingbidsthatreflectedwhattheysawasthetrueworthofthelicences,andpreventedthemcolludingtopaylowerprices.ProfHurwiczbeganworkingonformsofgametheorywiththeinfluentialeconomistKennethArrow,whofirstoutlinedthepitfallsofinformationasymmetryinthe1960sandwasawardedtheNobelprizeineconomicsin1972.ButArrow'sworkbuiltonsomeofHurwicz'sresearchinthe1950s,andHurwiczwasregardedashavingbeenoverlooked,untilnow.Myersonisaprolificauthorofacademicpapersandcomputersoftwaretacklingthesubject.Heisbestknownasoneoftheauthorsofaninfluentialprincipleinmechanismdesigntheory,theMyerson-Satterthwaitetheorem,whichfindsthatonesideofatransactionstandstomakealossofsomekindwhentwopartiestradeagoodwheretheyeachhavehiddenanddifferinginformation.Maskinhasworkedontheoptimaldesignofauctions,alongsidehiscolleagueJohnRiley,andwashiredtoadvisetheItaliangovernmentontheoperationofitsbondauctions.HehaspreviouslyworkedasaresearchstudentandvisitingfellowatCambridgeUniversity.RationalExpectationsTheoryAneconomicideathatthepeopleintheeconomymakechoicesbasedontheirrationaloutlook,availableinformationandpastexperiences.Thetheorysuggeststhatthecurrentexpectationsintheeconomyareequivalenttowhatthefuturestateoftheeconomywillbe.Thiscontraststheideathatgovernmentpolicyinfluencesthedecisionsofpeopleintheeconomy.Economic-behaviorobservationaccordingtowhich:⑴Onaverage,peoplecanquitecorrectlypredictfutureconditionsandtakeactionsaccordingly,eveniftheydonotfullyunderstandthecause-and-effect(causal)relationshipsunderlyingtheeventsandtheirownthinking.Thus,whiletheydonothaveperfectforesights,theyconstructtheirexpectationsinarationalmannerthat,moreoftenthannot,turnouttobecorrect.Anyerrorthatcreepsinisusuallyduetorandom(non-systemic)andunforeseeablecauses.(2)Inefficientmarketswithperfectornearperfectinformation(suchasinmodernopen-marketeconomies)peoplewillanticipategovernment'sactionstostimulateorrestraintheeconomy,andwilladjusttheirresponseaccordingly.marketswithsearchfrictionsSearchfrictionsareparticularlyimportantinth