語言文化論文-AGING AND PRODUCTIVITY AMONG ECONOMISTS.doc

語言文化論文-AGINGANDPRODUCTIVITYAMONGECONOMISTSAbstract-Economistsproductivityovertheircareersandasmeasuredbypublicationinleadingjournalsdeclinesverysharplywithage.Thereisnodifferencebyageintheprobabilitythatanarticlesubmittedtoaleadingjournalwillbeaccepted.Ratesofdecliningproductivityarenogreateramongtheverytoppublishersthanamongothers,andtheprobabilityofacceptanceisincreasinglyrelatedtotheauthorsqualityratherthantheauthorsage.Itiswellknownthatproductivitydeclineswithageinawiderangeofactivities.Lehman(1953)suggestsanearlypeakinproductivityinavarietyofscientificandartisticendeavors,andDiamond(1986)documentsthepatternforseveralscholarlypursuits.LevinandStephan(1992)provideclearevidencethatthisdeclineexistsevenaftercarefulattemptstoaccountforindividualandcohortdifferences.Fair(1994)findsdeclinesinphysicalabilityamongeliterunners,asdoesLydall(1968,pp.113passim)inphysicalabilitiesofthepopulationgenerally.Inthisstudyweexamineproductivitydeclinesinourownfield.Themainnewresultsarisefromouruseoftwodifferenttypesofinformation,theequivalentofhouseholdandestablishmentdata,tostudythestonefieldoveressentiallythesameperiodoftime.SectionIdiscussesthegeneralresultsonagingandproductivity,whereassectionIIpresentsevidenceoftheimportanceofheterogeneity.I.DecliningProductivitywithAgeUsingtheAmericanEconomicAssociation(AEA)DirectoryofMembers,weidentifiedtenuredeconomicsfacultyat17topresearchinstitutionsandobtainedtheyearsoftheirPh.D.degrees.1WiththecitationindexoftheJournalofEconomicLiteraturewereplicatedportionsofthecurricalavitaeofeachofthe208economistscurrentlyintheeconomicsdepartmentsofthoseinstitutionswhoreceivedPh.D.degreesbetween1959and1983.2Tomeasureproductivityweconstructthreeindexes,combiningpaperspublishedinrefereedjournals.Priorresearchsuggeststhat,atleastintermsofsalarydetermination,thereturnsfromnonreferredpublicationsarequitelowSauer(1988),sothatweignoresuchpublicationsincalculatingthesemeasures.I1weightsanarticlebythejournalwhereitappearsbasedoncitationstothatjournal,usingvaluesgeneratedbyLabandandPiette(1994).Thisindexdistinguishesstronglyamongjournals.Forexample,theJournalofPoliticalEconomyhasaweightof59.1,whereasEconomicInquiryhasaweightof7.9.InconstructingI1weusetheweightsassociatedwiththedecadeinwhichthearticleswerepublished.I2distinguishessomewhatlessamongjournalsbyassigningallarticlesintheninecorejournalsidentifiedbyLabandandPietteavalueof1,whereasallotherjournalsarevaluedat0.5.3Finally,I3givesallpapersaweightof1.Coauthoredarticlesweregivenhalfcredit,consistentwithSauers(1988)findingsontheeconomicreturnstocoauthorship.4Wemeasurethechangeinproductivityoverthelifecyclebythepercentagechangeinthenumberofpublicationsfrom9-10yearspastthePh.D.totheperiods14-15yearsandthen19-20yearsafter.Formostoftheeliteeconomiststhebaseperiodisequivalent(accountingforpublicationlags)tothetimeoftenure,whenonemightexpectthatincentivestoproduceareatapeak.Usingtwo-yearpublicationrecordsateachpointreducestheeffectsofnoiseintheperformancemeasures.Onemightarguethatstillotherscientificlife-cyclemileposts(e.g.,attainingafullprofessorship)shouldbeaccountedfortoo(andtosomeextentthe14-15-yearpointdoesthis).Butourmainpurposeissimplytoprovidedetailedevidenceontherelationshiptoage,andourdataarenotsufficienttoinfertheimpactofeverypossiblemilepost.Table1containsdataonproductivitylossbyPh.D.vintagemeasuredbyeachofthethreeindexes.IfweconsiderI1andI2,thetwoindexesthattakejournalqualityintoaccount,thedeclineappearstobequitesubstantial.Betweenyears9-10and14-15eliteeconomistsasagrouplose29to32%oftheiroutput.Fromyears9-10to19-20theylose54to60%.Inotherwords,productivitylossesareontheorderof5%peryearfromthetimeofpeakproductivity.However,thelossesdonotappeartoaccelerateoverthese10yearsoftheeconomistsworklives.Thelossfromyear10toyear20isapproximatelytwicethatfromyear10toyear15.Anotherwaytostudytheage-productivityrelationshipistoexaminejournalsratherthanindividuals.Thefirstrowineachpairofyearsintable2showstheagesofauthorsoffull-lengthrefereedarticlesinseveralleadingjournals(AmericanEconomicReview,JournalofPoliticalEconomy,andQuarterlyJournalofEconomics).5Themedianageofauthorsinthe1980sand1990swas36.Scholarsoverage50whentheirstudiesarepublishedareaminutefractionofallauthorsinthesejournals.Creativeeconomicsatthehighestlevelsismainlyfortheyoung.Thatisastrueinthe1990sasitwasinthe1960s,althoughtheagedistributionofauthorsdoesseemtohaveshiftedslightlyrightwardinthelate1970s.Thesecondrowineachpairintable2showstheagedistributionsofrandomsamplesofthemembershipoftheAmericanEconomicAssociationinyearsnearthoseforwhichtheauthorsagesweretabulated.6Thedistributionsareheavilyconcentratedbetween36and50.DecadalvariationsreflectrapidexpansionofAmericanuniversitiesinthemiddleandlate1960s,stagnationinthe1970sandmuchofthe1980s,andapossiblefragmentationoftheprofessioninthe1980sasspecializedassociationsexpanded.AsubstantialpercentageofAEAmembersisoverage50implyingthatoldereconomistsaregreatlyunderrepresentedamongauthorsinmajorjournalsrelativetotheirpresenceamongthosewhoviewthemselvesaspartoftheeconomicsprofession.7AmongtheseveralgroupsofphysicalscientistsanalyzedbyLevinandStephan(1992)thedeclineofproductivity(high-qualitypublishing)withagewasverypronounced.McDowells(1982)smallsamplesofscholarsinavarietyofdisciplinessuggestlessrapiddeclinesinproductivitywithage(inpublicationsunweightedbyquality),withthesharpestdeclinesandearliestpeaksinthehardsciences,andlaterpeaksamongEnglishprofessorsandhistorians.Theevidencefromourtwoverydifferenttypesofsamplesofeconomistsandeconomicspublishingthataccountforthequalityofpublicationssuggeststhat,forwhateverreason,economicsisatleastasmuchayoungpersonsgameasarethephysicalsciences.II.HeterogeneityinDecliningProductivityTheevidenceinsectionIdocumentsthedeclineinproductivityatthesamplemeans.Informationontheage-productivityrelationshipattheextremesofthesampleisinterestinginitsownrightandmighthelpshedsomelightonthepossiblecausesoftheapparentdeclineinproductivitywithage.Thesimplesttestcomparesproductivitylossesamongthetopearlyperformerswiththatoftheentiresampleofeconomistsateliteinstitutions.Amongthetop10%ofearlyproducersthemeanvaluesofI1,I2,andI3atyear20were64,50,and22%,respectively.Thesemeansarequiteclosetothoselistedfortheentiresampleintable1.Thusonaverageearlypromiseseemstobesustainedinthissample.Ofthe12topresearchersonwhomwehave20yearsofdata,fivewerestillamongthetopdozenproducersatyear20.Theseconclusionsareconfirmedwhenweexaminetheentiresample.ForeachindexIj,j=1,2,3,weestimateb0andb1inMultiplelineequation(s)cannotberepresentedinASCIItext.(1)Table3reportstheparameterestimates.Forallthreeindexesproductivityinyear20ispositivelyandsignificantlyrelatedtoproductivityinyear10.Thereisalsosubstantialproductivityloss.Thejointhypothesisthatb0=1andb1=0(i.e.,noproductivityloss)isrejected(F-statisticsof134,152,and39,respectively).ProductivitylossisleastsevereinI3,whichweightsalljournalsequally,regardlessofquality.Ifproductivitylosseswerelessamongeconomistswithhighearlyproductivity(highIj,10),b1wouldbenegative.Infact,fortwoofthethreeindexestheestimatedb1iseffectivelyzero.Wecannotrejectthehypothesisofalinearrelationshipbetweenlateandearlyproductivity.OnlyforI3doesitappearthatproductivitylossishigherfortopearlyproducers,andevenheretheeffectisquitesmall.Aneconomistinthetop10%ofthissampleatyear10losesonlyanadditional0.5(unweighted)papercomparedtoanaverageresearcherinthissampleatyear10.Theverytopproducersinthiselitesamplekeeponproducinghigh-qualityresearch,butataslowerrate.Thosewhowerenotatthetopearlyintheircareersslowdownasrapidlyasthetoppeople,buttheirslowdownleadsthemtopublishincreasinglyinlowerqualityoutlets.Anotherwayofexaminingheterogeneityistolookathowauthorsofdifferentqualityfreeinthepublicationprocessconditionalontheirefforts.Weobtaineddataonarandomsampleofinitialsubmissionstoamajorgeneraljournalduringafour-monthperiodin1991.(SomeofthedatawereinitiallysuppliedbythejournalsofficeforuseinHamermesh(1994).)Refereeingatthisjournalisdouble-blind,sothatthechancethatreferees(thoughpossiblynottheeditors)wereaffectedbyauthorsreputationsisreduced.Theagesoftheauthorsofthese313papersaremeasuredasof1993toaccountfortheprobabletwo-yearaveragelagbetweenthesubmissionofapaperanditspublication.Thesimplefactintheseadditionaldataisthatacceptanceratesatthisjournalareremarkablyconstantbyauthorsage.Theprobabilitiesofanarticlebeingacceptedare0.122,0.114,and0.123inthethreeagegroups50,respectively.8Onaveragethereisnodeclinewithageintheacceptancerateofpaperssubmittedtothisjournal.9ProbitsontheacceptanceofasubmissionthatalsoincludedvariablesindicatingwhethertheauthorwasamemberoftheAEA,wasinatop20department(aslistedinBlank,1991),wasresidentinNorthAmerica,orwasfemale,andtheauthorspriorcitationrecordyieldanidenticalconclusion.Thedecliningpresenceofolderauthorsintopeconomicsjournalsdoesnotoccurbecauseolderauthorswhokeepsubmittingpaperssufferhigherrejectionrates.Theprobitsincludedinteractiontermsbetweenindicatorvariablesforageandtheextentofcitations.(Low-citedeconomistsweredefinedasthosewithfewerthan10citationsperyear,well-citedwithatleast10.)Asfigure1clearlyshows,acceptanceratesforeachagegroupdiffersharplybycitationstatus.Comparingauthorsage36-50tothoseover50,itisquiteclearthatthedegreeofheterogeneityincreaseswithage.Thisappearstobelesstrueincomparingtheoldesttotheyoungestgroup,butthatinferenceisduemainlytoaverysmallsample.(Onlysixauthorsunderage36,thefuturesuperstarsoftheprofession,werewellcited.)Thegeneraltenorofthecombinedresultsfromthissampleisthattheprofessionsignalstolessablescholarsthattheirworknolongermeetstheprofessionshigheststandards,andmostofthemrespondbyred