Publication rate expressed by age, gender and academic position - A large-scale analysis of Norwegian academic staff

Journal of Informetrics

jo u r n al hom e p ag e :w w w . e l s e v i e r . c o m / l o c a t e / j o i

Publication rate expressed by age, gender and academic position – A large-scale analysis of Norwegian academic staff

Kristoffer Rørstad

, Dag W. Aksnes

NIFU–NordicInstituteforStudiesinInnovation,ResearchandEducation,Wergelandsveien7,NO-0167Oslo,Norway

a rt i c l e i n f o

Articlehistory:

Received1October2014 Receivedinrevisedform 13December2014 Accepted4February2015

Keywords:

Publication Productivity Age Gender Academic Position

a b s t ra c t

Thisstudyinvestigateshowscientificperformanceintermsofpublicationrateisinfluenced bythegender,ageandacademicpositionoftheresearchers.Previousstudieshaveshown thatthesefactorsareimportantvariableswhenanalysingscientificproductivityatthe individuallevel.Whatisnewwithourapproachisthatwehavebeenabletoidentify therelativeimportanceofthedifferentfactorsbasedonregressionanalyses(OLS)ofeach majoracademicfield.Thestudy,involvingalmost12,400Norwegianuniversityresearchers, showsthatacademicpositionismoreimportantthanageandgender.Inthefieldsanalysed, theregressionmodelcanexplain13.5–19percentofthevarianceinthepublicationoutput atthelevelsofindividuals.Thisalsomeansthatmostofthevarianceinpublicationrateis duetootherfactors.

©2015TheAuthors.PublishedbyElsevierLtd.ThisisanopenaccessarticleundertheCC BY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

Itiswellknownthattherearelargedifferencesinthepublicationoutputbetweenscientists:arelativelysmallproportion ofscientistscontributetothemajorityofthepublications.In1926Lotkaformulatedthefamousinversesquarelawof productivity,whichstatesthatthenumberofauthorsproducingnpapersisapproximately1/n²ofthoseproducingone (Lotka,1926).Thismeans,forexample,thatofallauthorsinagivenfield,60percentwillhaveproducedjustonepublication.

Alargenumberoflaterstudieshaveconfirmedthatthereexistsahighlyskewedproductivitypatterninscientificpublishing (e.g.Allison&Stewart,1974;Price,1986;Reskin,1977).However,ithasalsobeenshownthatthedifferencesinscientific publicationrateatthelevelofindividualsarefewerthanindicatedbyLotka,andthatLotka’slawoverestimatesthenumber ofpapersproducedbythemostprolificscientists(Kyvik,1991;Potter,1981).

Thereasonfortheskeweddistribution,andforindividualpublicationratedifferencesmoregenerally,hasalsobeen thetopicofmanysubsequentstudies.Here,attentionhasbeendirectedtowardsfactorsattributedtosocialdynamics(e.g.

cumulativeadvantage,theMattheweffect(Merton,1968))andtomorespecificfactorslikeageandacademicpositionof thescientists.Inthisstudy,wearefocusingonthelattersetoffactors.Weaskwhetherscientificpublicationratecanbe expressedbytheage,genderandacademicpositionoftheresearchers.Ifso,towhatextentdothesevariableshaveany effectonscientificperformanceintermsofpublicationoutput?Previousresearchhasshownthatallthesevariableshave aneffectonscientificproductivity,buttheresultsofthedifferentstudieshavenotbeenentirelyconsistent.

First,thescientificpublicationratehasbeenfoundtoincreasewithinthehierarchyofacademicpositions:professorsare themostprolificpersonnelwhilepeopleinloweracademicpositionstendtopublishfewerpublicationsperyear(seee.g.

∗ Correspondingauthor.Tel.:+4722595179.

E-mailaddresses:[email protected](K.Rørstad),[email protected](D.W.Aksnes).

http://dx.doi.org/10.1016/j.joi.2015.02.003

1751-1577/©2015TheAuthors.PublishedbyElsevierLtd.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/

licenses/by-nc-nd/4.0/).

isthatwomenoccupyfewerofthehighestacademicpostsandalsoarelessintegratedinthescientificcommunity,for examplebypositions/membershipinscientificassociationsandontheeditorialboardsofjournals(Bentley&Blackburn, 1992;Cole&Zuckerman,1984;Luukonen-Gronow&Stolte-Heiskanen,1983;Prpic,2002;Puuska,2010;Xie&Shauman, 1998).Nevertheless,studieshavealsoshownthatdifferencesinpublicationrateamongmenandwomencanbefoundat alllevelsofacademicpositions(Aksnesetal.,2011;Kyvik,1991).Asanexplanationofthegenderdifferences,ithasbeen suggestedthatwomenandmenchoosedifferently(Ward&Grant,1996).Whilewomendevotemoretimetoteachingand administrativework,malescientistsfocusmoreonresearchandsupervisionofPhDstudents.However,arecentstudyon Dutchsocialscientistsfoundthatyoungfemaleresearchersoutperformedyoungmaleresearchersintermsofnumberof publications(vanArensbergen,vanderWeijden,&vandenBesselaar,2012).

Finally,therelationshipbetweenageandpublicationratehasbeenfoundtobecurvilinearinseveralstudies.Theaver- ageproductionofpublicationsincreaseswithageandreachesapeakatsomepointduringthecareerandthendeclines (seeforinstanceAksnesetal.,2011;Barjak,2006;Cole,1979;Gonzalez-Brambila&Veloso,2007;Kyvik,1990).However, Kyvik(1990)alsonotedthattheresearcherswithmorerecognitionkeeppublishingfrequentlyaftertheirless-recognised colleaguesreachedtheirpeak.

Inthislarge-scalestudy,wehaveinvestigatedtheinfluenceofage,genderandscientificpositiononscientificpub- licationrate.Thisisdoneseparatelywithinmajoracademicfields.Whilemostpreviousstudieshaveinvestigatedthese variablesindividually,weinthismultivariatestudyhaveanalysedallthreefactorsatthesametime(cf.Puuska,2010;Shin

&Cummings,2010).Ourobjectiveshavebeentoidentifythevariableswhicharemostinfluentialintermsofexplaining differencesinpublicationrates,andwhetherthesamefactorsareinfluentialacrossallacademicfields.

Mostpreviousstudieswhichhaveinvestigatedthesefactorshavemeasuredthepublicationoutputofeachscientist duringacertainperiod.Inthisstudy,wehaveusedthepublicationoutputperscientistperyearasameasure(notthe averageforalongerperiod).Asaresult,thefiguresareadjustedforthetimearesearcherhasbeenemployedinanacademic position.

Typically,previousstudieswhichhaveaddressedthesequestionshavebeenrestrictedtothedataavailablefromlarger bibliometricdatabases,inparticulartheWebofScience(ThomsonReuters).Suchanalysesoftenproduceadistortedpicture oftheresearchoutputinsomedisciplines,inparticularthesocialsciences,artsandhumanities,whereasubstantialshare ofrelevantjournalsorbooksarenotindexedintheWebofScience(Hicks,2004).Thisstudy,ontheotherhand,isbasedon completepublicationdata(scientificandscholarlypublications)forallresearchersemployedatNorwegianuniversities.As aresult,thesocialsciencesandhumanitiesarefullycoveredinouranalyses.

Norwayiswellsuitedasacaseforanalysingthisissue.Uniquedatasetsareavailablenotonlyontheresearchoutput butalsoontheresearchstaff.Norway’shighereducationsectorcomprisesfourtraditionaluniversities,fourspecialised universitiesaswellasanumberofuniversitycolleges.TheacademiccareersystemconsistsofPhDcandidates,postdocs, associateprofessorsandfullprofessorsasthemainpositions.AfterobtainingaPhDdegree,oneisentitledtoapplyfor permanentpositionsasassociateprofessorortemporarypositionsaspostdocs.Contrarytomanyothercountries,associate professorsareeligibletoapplyforpromotiontofullprofessoronthebasisoftheirindividualresearchcompetence(in accordancewithinternationalornationalstandardswithinthesubjectarea),irrespectiveofvacantprofessorships(Olsen, Kyvik,&Hovdhaugen,2005).

Itshouldbenotedinitiallythatinpreviousliterature,scientificproductivityoftenhasbeenusedasconceptforthe input–outputrelationship,typicallyexpressedasthenumberofpublicationsofaresearcherduringagiventimeperiod.

Productivitymayhaveconnotationstoefficiency,whichisamorecomplexissue,involvingconsiderationofoptimaltime use,spendingofresources,etc.Wehavethereforeinthisstudymainlyusedpublicationrateasaconceptfortherelationship, whichpreviouslyusuallyhavebeentermedpublicationproductivity.

2. Methodsanddata

Inourstudy,weappliedtheNorwegianpublicationdatabaseCurrentResearchInformationSysteminNorway(Cristin).

Thisdatabaseincludesalltypesofscientificandscholarlypublications,inallfieldsofresearchinthehighereducation sector.Bibliographicdataarecollectedthrougha commondocumentationsystemusedbyallinstitutions,resultingin

Humanities 1340 3691

Socialsciences 1979 5821

Naturalsciences 3151 9558

Engineeringandtechnology 1912 4757

Medicine 4021 11,974

Total 12,403 35,798

complete,verifiableandstructureddataforuseinbibliometricanalysis(Schneider,2009;Sivertsen,2010).Inthedatabase, publicationoutputisreportedbytheinstitutionsasstandardbibliographicreferences,whichareanalysablebypublication channelandtypeofpublication.Adynamicauthorityrecord,covering19,000controlledscientificandscholarlypublication channelsensuresthatnon-scientificpublicationsarenotenteredintothesystem.¹ Nationalpublishingboardsineach disciplineareresponsiblefortheapprovalofpublishingchannelsaccordingtospecificnationalcriteriaandguidelines(e.g.

onlyjournals,series,andbookpublisherswithpeerreviewsystemscanbeapproved).Publicationdatafromprofessional bibliographicdatasources(e.g.theWebofScience)areimportedtotheCristinsystem,tofacilitatetheregistrationof publicationsbytheemployees.Atinstitutions,therearelocalroutinestocheckthatallpublicationshavebeenregistered.

Thus,missingpublicationsbyresearchersislikelytobeaveryminorproblemandoverallthepublicationdatahaveexcellent quality.Thedatabaseisthereforewell-suitedtopublicationanalysesacrosssubjectfields,asalargescaledatabase,with completecoverageofallpeer-reviewsscientificandscholarlypublicationoutput,includingjournalarticles,monographs, bookchaptersandconferenceseries.

AsabasisforthestudyweselectedthefourmajorNorwegianuniversities(UniversityofOslo,UniversityofBergen,The NorwegianUniversityofScienceandTechnologyinTrondheim,andtheUniversityofTromsø)whichaccountforabout70 percentofthetotalpublicationoutputofthehighereducationsectorinNorway.Ouranalysiscoversthe7-yearperiodfrom 2005to2011.

Toprovideinformationonindividualcharacteristicsoftheresearchers(fieldofscience,position,ageandgender),the bibliographicdatabasewascoupledwithanotherdatabase,theNorwegianResearchPersonnelRegister(providingtheoffi- cialNorwegianR&Dstatistics,compiledbyNIFU).Thisdatabasecontainsindividualdataforallresearchersinthehigher educationsectorandinstitutesectorinNorway(withbiennialdatafrom1977to2007,andannualdatafrom2008).The researchershaveuniqueIDsinboththeResearchPersonnelRegisterandtheCristinpublicationdatabase.However,theIDs arenotidentical.Thelinkingisbasedondataonthefullnameoftheresearchersaswellastheirinstitutionalaffiliations.

Foralargenumberofindividuals,thereisaone-to-onecorrespondence,andhomonyms(differentpeoplewithidentical names)donotrepresentaproblem.Inourstudywehavelinkedresearcherswithidenticalnamesmanuallyusingavailable dataandinformation.

Thecouplingofthesetwodatabasesresultedinadatasetweanalysed,containingabout12,400peopleinalmost35,800 observations(i.e.publicationnumbersperyears).Thus,thereareonaveragealmostthreeobservationsperpersonanalysed.

Non-publishingpersonnelhavenotbeenincludedinthestudyasonlypeoplewhohavepublishedareregisteredinthe database.Thismayberegardedasalimitationofourstudyastheinclusionofthenon-publishingresearcherscouldpossibly increasethepublicationratedifferencesbetweengenders,agegroupsandpositions.Probably,manyoftheresearcherswho arenotfoundinthedatabase(andhavenotpublished)arenewlyappointed,andthusunproductive.Othershavenotpub- lished,foravarietyofreasons.Althoughitwouldhavebeenpreferabletohavedataonnon-publishingpersonnelincluded, theadvantageofourapproachisthattheanalysisisbasedonpeoplewhoevidentlyareactiveresearchers.Moreover,biases causedbymobileresearchersarereduced.Whenaresearcherisnewlyappointedataparticularuniversity,itusuallytakes sometimebeforetheresearchendsupinpublications.

Intheanalysis,allpersonswereassignedtofivemajorfields;thehumanities,socialsciences,naturalsciences,engineering andtechnologyandmedicine(cf.Table1).Thisassignmentwasbasedonthedepartments’reportingoftheirscientificprofile innationalR&Dstatistics(departmentsselectfromalistof58scientificsubfieldswithinthefivemaindomains).Wehave previouslyanalysedpublicationrateatsubfieldlevels,partlybasedonthesamedatamaterial.Thisanalysisshowsthatthe largestdifferencesinpublicationpatternsandratesarefoundacrossthebroadfields(Piro,Aksnes,&Rørstad,2013).Within eachfieldthepublicationpatternismoreuniform,althoughwithnotableexceptions.Basedonthesefindingswedecided nottoincludesubfieldasavariableinthepresentstudy.

Publicationoutputhasbeenmeasuredasarticleequivalentsperpersonperyear.Inthiscalculation,co-authoredpubli- cationsarefractionalisedamongtheauthors.Moreover,monographsareweightedasequaltofivearticles(injournalsor books)inordertomaketheresearcheffortsbehinddifferenttypesofpublicationscomparable.Theweightingofbooksis basedonKyvik’ssummaryofsuchweightingproceduresfromotherstudies,whichshowsthatmoststudiesequate4–6 articlestoonefullmonograph(Kyvik,1991).TheNorwegianandDanishperformancebasedfundingmodelalsoequalsone

1Thelistcanbedownloadedat:https://dbh.nsd.uib.no/publiseringskanaler/Forside?sok.avansert=true&requestlocale=en.

Fig.1.Articleequivalents(mean)byfieldsandgender(N=35,798).

monographwithfiveregularjournalarticles(Sivertsen,2010).IntheFlemishperformance-basedfundingsystemforuniver- sityresearchbooksareassignedaweightfactorof4articles(Engels,Ossenblok,&Spruyt,2012).Theweightingprincipleis admittedlysomewhatrandomasnoempiricalinvestigationhasbeencarriedoutofthetimeandeffortsneededfordifferent typesofpublications.Itshouldbenotedthatmonographsaccountsforaverysmallproportionofthepublications,overall 2.6percent,andonlyinthehumanitiesandthesocialsciencesthispublicationtypehasacertainvolume(proportions:10.5 and6.6percentoftheobservations).WehaveshownthepublicationpatternforbooksweightedinFig.1andnon-weighted inFig.2.

Inouranalysis,weincludedfourmainacademicpositions:professors,associateprofessors,postdocsandPhDstudents.In addition,physicians/medicaldoctorswereincludedformedicine.Theresearchersweredividedinto5-yearagecategories.

Althoughwe mightlosesomeoftheinformation,ageintervalssimplifythedescriptivepresentationandareeasierto interpret.Thedescriptivestatisticsalsoshowthattheagecategoriesbehavelinearly.Itshouldalsobeaddedthatthereisa time-lagfromtheresearchiscarriedouttilltheresearchappearaspublishedarticles(usually1–2yearsorlonger).

Ourstudyinvolvescross-sectionaldata.Wehaveanalyseda7-yearperiodbuthaveusedannualpublicationcountsand havenottracedthedevelopmentofthepublicationrateoftheindividualresearchersoveraperiod.Foreachresearcher thereisamaximumofsevenobservations,butformanyindividualswehavefewerobservationsbecausetheyhavenotbeen employedduringtheentireperiodorhavenotpublishedparticularyears(cf.Table1).Theageandpositionoftheresearchers havebeenadjustedaccordingly.Forexample,apersonwhowaspromotedfromassociateprofessortofullprofessorin2009 isincludedasanassociateprofessorforthe2005–2008observationsandasaprofessorforthe2009–2011observations.

Cross-sectionalmethodologyisgenerallyregardedashavingmoreweaknessesthanlongitudinalmethodology(Allison&

Stewart,1974;Stephan,1996).Nodoubt,alongitudinalstudywouldhaveprovidedinterestingcomplementaryresults.As thestudydoesnotfocusonanalysingchangesinpublicationrateattheindividuallevelovertime,wehavechosenacross- sectionalapproach.Itshouldalsobeaddedthatthenormsforpublicationbehaviourhavechangedduringrecentdecades (e.g.byanincreasingnumberofauthorsperpublicationandnumberofpublicationsperperson(Kyvik&Olsen,2008)),and thiscomplicatestheinterpretationofresultsobtainedbylongitudinalmethods.

Fig.2.Articleequivalents(mean)(booksunweighted)byfieldsandgender(N=35,798).

Fig.3. Distributionofnumbersofaveragearticleequivalentsperpersonperyearandnaturallogarithmicnumbers(N=35,798).

Inordertobeabletomakeregressionmodelsonourdata,werecodedourvariables.First,positionswererecodedto numericalcategoricalvariables,thendummyvariableswereusedforeachposition(1ifpresentand0ifnotpresent).Gender wasalsorecodedthesameway(men=0andwomen=1).Agegroupswerecategorisedintoanordinalvariablei.e.20–24 years=1,25–29=2,30–34=3andsoforth.Theresponsevariablerangedfrom0.0003to20.33,whichafterlogtransformation amountedtobetween−8.06and3.01.

Thepublicationratevariessignificantlyamongtheindividuals, andisnotnormallydistributed.A histogramofour publicationindicatorshowsapositiveskewinFig.3.Acommonwaytoeliminateskewnessistotransformthedatato naturallylogarithmicscale.Densitychartsofthelogarithmicofthepublicationindicatorforeachmajorfieldareshownin theAnnex.Thesechartsshowthattheobservationsfornaturalsciences,engineeringandtechnologyandmedicine,have anormallydistributedshape.However,forthehumanitiesandsocialsciences,thelogarithmicofthepublicationratewas notnormallydistributed.Thismeansthatthedatainthelattertwofieldsviolatelinearregressionassumptionsandsuch regressionanalysiscanonlybeconductedwithsatisfactorilyresultsinthefirstthreefields.

Weanalysedthepublicationoutputbyfieldsofsciences,academicposition,agegroupsandgender.Regressionanalysis wasperformedonthreeofthemajorfieldsseparatelyinordertoinvestigatewhetheroneregressionmodelisvalidforall fields.

Sincewepreviouslyhavefoundthatageandpublicationrateoftenhaveacurvilinearrelationship,weincludethepower ofageinourregressionmodel.Ourassumptionthatpublicationrate(numberofarticleequivalentperpersonperyear)isa functionofgender,ageandscientificposition,ourregressionmodelcanbewrittenas:

Log(Y)=ˇ0+ˇ1∗age+ˇ2∗age²+ˇ3∗gender+ˇ4∗position+ε (1) Werecognisethatareversecausalitybetweenpublicationrateandacademicpositionmaybepresent,asscientificpub- licationoutputisoneofseveralcriteriaforadvancementwithintheacademiccareersystem.Inordertoinvestigatethis problemfurther,werearrangedthedatainsuchwaythatoneresearcherrepresentedoneobservation.Anew“career- change-variable”wasalsointroduced.Outofthe12,304researchers,10,594researchers,accountingforabout85percent, hadthesamepositionthroughouttheperiod,whilsttherest,1809(i.e.15percent)hadacareerchangeduringtheperiod.

Thepurposeofthisanalysiswastoinvestigatewhetherresearcherswithacareerchangehadahigheraveragepublication rateintermofpublicationoutput,thanthosewhowereinthesameacademicposition.

Theresultoftheanalysisshowedthatacareerchangedidnothaveanyeffectonpublicationrateasthisvariablewasnot significantfornoneofthemajorfield.Thepublicationrateforeachresearchercanthereforeberelatedbythepositionthe researcherhadduringthestudiestimeperiod.Ourdataarethussuitabletoexaminepublicationratebyacademiclevels.

3. Results

ThedistributionofthepopulationbyfieldsintermsofnumbersofresearchersandobservationsisgiveninTable1.

Medicineisthelargestfieldandaccountsforaboutone-thirdofthepopulation,intermsofbothpersons(4021)andobserva- tions(11,974).Withabout1340personsandabout3700observations,humanitiesisthesmallestfield,butwithasufficiently largepopulationtoanalyseseparately.

Fig.1showstheaveragenumbersofarticleequivalentsperpersonperyearbygenderandfields.Thisfigureshowsthat therearemajorinequalitiesinthepublicationrateacrossfields.CorrespondingresultswerealsofoundbyPiroetal.(2013), andjustifythedecisiontocarryoutregressionanalysisofeachfieldseparately.

Fig.4. Articleequivalents(mean)bygenderandagegroupsforallfields(N=35,798).

Fig.4showsthepublicationrateforthewholepopulationbyagegroupandgender.Thepublicationrateofwomen increasescontinuouslybyage,inanalmoststraightline(thelowerdarkerlineinFig.4),whilethepublicationrateofmen showsacurvilinearshape.Overallmenhavehigherpublicationratethanwomenuptotheageof55–59years.

Thepersonsover70aremainlyemeritusprofessorswhohaveformallyretired.Onlythepersonswhoarestillactive researchersareincluded(i.e.havepublishedatleastonepublication).Itshouldbenotedthatthisgroupofpersonsisrather heterogeneousandtheextenttheyarestillinvolvedinresearchmayvary.Someareveryactiveandspendmuchtimeon research,othersdoresearchonlyoccasionally.Thetotalnumberofobservationsbythisgroupis673,orlessthan2percent, anddonotmakeanydifferencefortheanalysis.Hence,theywerenotexcludedfromthedata.

3.1. Analysisofnaturalsciences

Table2showstheaveragenumberofarticleequivalentsperpersonperyearbyacademicpositionandgender.Over- all,we canobserveanincreaseinpublicationratefromPhDstudentstoprofessorsinthenaturalsciences.Moreover, forallpositionsfemalescientiststendtohavelowerpublicationratesthantheirmalecolleagues.Onaverage,menhave 0.34morearticleequivalentsannuallythanwomen.Theoverallgenderdifferenceislargerthanintheindividualposition categoriesduetoalargershareoffemaleresearchersinthecategorieswithlowestpublicationrate(PhDstudentsand postdocs).

Dividedbyagegroups,curvilinearrelationshipsbetweenpublicationrateandagecanbeseenwithseveralpeaks.In addition,menhavehigherpublicationratethanwomeninallbutoneageinterval.

Inordertotestwhetherthesevariablescanbeusedtopredictthepublicationratelevel,wecarriedoutanordinary leastsquaresregressionanalysis.Theresultsfromourregressionmodelshowthatbothgenderandacademicpositionare statisticallysignificantvariables,whileageandagesquaredarenot.AsseeninFig.5,thepublicationratedoesnothavea linearoracurvilinearrelationshipasassumed.Thechangeinpublicationrateinpercent,causedbyavariable,isgivenby theunstandardisedregressioncoefficientB,andcanbeexpressedase^B−1.Theregressionanalysisthusshowsthatwomen publishabout22percentfewerpublications(articleequivalents)onaveragethantheirmalecolleaguesareatsameageand

Table2

Articleequivalents(mean)byacademicpositionandgenderinthenaturalsciences(N=9558).

Academicposition Women Men Bothgenders Diff.,men−women

Professors 0.91 1.14 1.11 0.23

Associateprofessors 0.61 0.86 0.80 0.25

Postdocs 0.44 0.65 0.59 0.21

PhDstudents 0.35 0.48 0.43 0.13

Total/average 0.53 0.87 0.79 0.34

Fig.5. Articleequivalents(mean)bygenderandagegroupsinnaturalsciences(N=9558).

Table3

Regressionanalysisofnaturalsciences.

Variables Std.beta Bcoef. Std.Err. t-Value P>t [99percentConf.Int.]

Agegroup −0.06 −0.02 0.025 −0.97 0.332 −0.074 0.025

Agegroupsquared −0.06 0.00 0.002 −1.11 0.266 −0.006 0.002

Gender −0.10^** −0.25 0.024 −10.42 0.00 −0.301 −0.206

Professors 0.16^** 0.33 0.032 10.47 0.00 0.271 0.395

Associateprofessors Ref.value

Postdocs −0.17^** −0.44 0.038 −11.52 0.00 0.164 0.289

PhDstudent −0.29^** −0.66 0.040 −15.81 0.00 −0.746 −0.582

Constantterm −0.32 0.058 −3.79 0.00 −1.099 −0.869

R-squared=0.1345,F-value=247.33,N=9558.

**Significantat0.01level.

insameacademicposition.Moreover,professorshaveonaverageabout40percenthigherpublicationoutputthanassociate professors,whilepostdocsandPhDstudentshaveabout35and50percentlower,respectively(Table3).

3.2. Analysisofengineeringandtechnology

Table4showsthatresearcherswithinengineeringandtechnologyhaveslightlyhigherpublicationrate(with0.96article equivalentsperpersonperyear)thantheircolleagueswithinnaturalsciences(with0.79)(seealsoFig.1andFig.2).Not surprisingly,professorsarethemostprolificpersonnel,followedbyassociateprofessors,postdocsandPhDstudents.Inthis field,womenaccountforlessthan20percentoftheobservationsandtheypublish0.30lessarticleequivalentsonaverage thanmen.Thegenderdifferencesinpublicationraterangefrom0.08forprofessorsto0.20forpostdocs.

Table4

Articleequivalents(mean)byacademicpositionandgenderinengineeringandtechnology(N=4754).

Academicposition Women Men Bothgenders Diff.,men−women

Professors 1.47 1.55 1.54 0.08

Associateprofessors 1.07 1.09 1.09 0.02

Postdocs 0.62 0.82 0.78 0.20

PhDstudents 0.52 0.61 0.59 0.09

Total/average 0.71 1.01 0.96 0.30

Fig.6.Articleequivalents(mean)byagegroupsinengineeringandtechnology(N=4754).

Ifwelookatpublicationratebyage,therearedifferentpatternsformenandwomen(cf.Fig.6).For bothgenders, publicationrateincreasesbyageuptoabout40–44years,thendeclinesformen,whilewomenremainatthesamepublication ratefortheirnext5years.Whilewomenreachapublicationpeakaroundtheirmid-fifties,theirmalecolleagueshaveaslight decrease,andthenfurtherincreasetheirpublicationoutputratetoapeakintheirsixties.Thispublicationpatternindicates thatageandagesquaredshouldbeincludedinaregressionanalysisforpredictingpublicationratesinengineeringand technology.

Theregressionanalysisofengineeringandtechnologygivesamodelwhereallvariablesaresignificant.Thesizeandsign ofthebetacoefficientsprovideinformationontheextentpublicationratecorrelatestoeachoftheindependentvariables.

Allofthevariablesaresignificantandbothageandagesquaredaremoreinfluentialstatisticallythangender.However,by comparingtheregressioncoefficients,thedifferencebetweenmenandwomenisslightlylarger(B=0.17)thanat5years older(B=0.12).Asforthenaturalsciences,professorsarethemostprolificpersonnelinengineeringandtechnology,and acorrespondingpatternofdecliningpublicationratescanbeseenwithinthehierarchyofacademicpositions.Explained varianceinthismodelisabout15percent,andthemodelisslightlymorepowerfulthanwhatwefoundfornaturalsciences (13.5percent)(Table5).

3.3. Analysisofmedicine

Table6showsthepublicationratebyacademicpositionandgenderwithinthefieldofmedicine.Overallmenhavehigher publicationratethantheirfemalecolleagues,butfemaleprofessorsandassociateprofessorsareslightlymoreproductive thantheirmalecolleagues.Onaverage,amaleresearcherwithinmedicinepublishes0.63articlesperyear,whileafemale researcherproduces0.47articles,whichgivesadifferenceof0.16articlesperyear.

Table5

Regressionanalysisofengineeringandtechnology.

Variables Std.beta Bcoef. Std.Err. t-Value P>t [99percentConf.Int.]

Agegroup 0.31^** 0.12 0.03 3.8 0.00 0.06 0.18

Agegroupsquared −0.33^** −0.01 0.00 −4.58 0.00 −0.02 −0.01

Gender −0.07^** −0.17 0.03 −5.18 0.00 −0.23 −0.10

Professors 0.16^** 0.31 0.05 6.12 0.00 0.21 0.41

Associateprofessors Ref.value

Postdocs −0.13^** −0.32 0.06 −5.73 0.00 −0.43 −0.21

PhDstudent −0.24^** −0.43 0.06 −7.72 0.00 −0.54 −0.32

Constantterm −0.55 0.10 −5.34 0.00 −0.75 −0.35

R-squared=0.1509,F-value=140.56,N=4754.

** Significantat0.01level.

Professors 0.97 0.95 0.96 −0.01

Associateprofessors 0.71 0.66 0.69 −0.05

Postdocs 0.40 0.47 0.43 0.07

PhDstudents 0.28 0.31 0.29 0.04

Medicaldoctors/physicians 0.38 0.50 0.47 0.12

Total/average 0.47 0.63 0.57 0.16

Fig.7. Articleequivalents(mean)byagegroups,medicine(N=11,974).

ScientificpublicationrateasafunctionofageisshowninFig.7.Thepublicationratepatternissimilartotheonefound forengineeringandtechnology.Women(thedarkergreyline)havelowerpublicationratethantheirmalecolleagueswithin thesameagegroup,uptotheirmid-fifties.Thentheybecomeequallyproductive,andintheirlatefiftiesapublicationrate peakcanbeseen,wherefemaleresearchershavehigherpublicationratethantheirmalecolleagues.

TheresultsoftheregressionanalysisareshowninTable7.About19percent(R-squared=0.1895)ofthevariance isexplainedinourregressionmodel,andisthusalittlemorepowerfulthanthemodelsforbothnaturalsciencesand engineeringandtechnology.Allvariablesarealsoshowntobesignificant.Ageanditssquaredtermisthemostimportant variable,followedbyacademicposition,whilegenderistheleastimportantvariable–butstillsignificant.Theaverage

Table7

Regressionanalysisofmedicine.

Variables Std.beta Bcoef. Std.Err. t-Value P>t [99percentConf.Int.]

Agegroup 0.40^** 0.15 0.018 8.31 0.00 0.117 0.190

Agegroupsquared −0.35^** −0.01 0.001 −7.72 0.00 −0.014 −0.008

Gender −0.04^** −0.08 0.017 −4.9 0.00 −0.117 −0.050

Professors 0.15^** 0.31 0.032 9.54 0.00 0.243 0.369

Associateprofessors Ref.value

Postdocs −0.12^** −0.35 0.037 −9.56 0.00 −0.422 −0.279

Medicaldoctors/physicians −0.20^** −0.40 0.031 −13.02 0.00 −0.466 −0.344

PhDstudent −0.28^** −0.59 0.034 −17.24 0.00 −0.656 −0.522

Constantterm – −1.23 0.066 −18.68 0.00 −1.360 −1.102

R-squared=0.1895,F-value=39.61,N=11,974.

**Significantat0.01level.

Fig.8.Articleequivalents(mean)byagegroups,socialsciences(N=5821).

differenceinpublicationratebetweenthegendersisonly8percentinfavourofmen;howeverat5yearsolderthepublication rateofbothmenandwomenwillonaverageincreaseby17percent.

3.4. Analysisofsocialsciences

AsshowninFig.1,researchersinsocialscienceshavehigherpublicationratethanresearchersinthenaturalsciences, engineeringandtechnologyandinmedicineintermsofarticleequivalents.Whilearesearcherinsocialsciencesproduces onaverage1.5articlesperyear,colleaguesinthehardsciencesproducedsomewherebetween0.6and1.0articlesper yearonaverage.Onepossibleexplanationforthesedifferencesisadifferentpublicationpatterninthesocial sciences comparedwiththepreviouslystudiedfields.Inthesocial sciences,onepublicationhasin generalfewerauthorsthan apublicationinmedicine,naturalsciencesandtechnology.Inaddition,researchersinthesocialsciencespublishmore monographs.

Onaverage,aprofessorpublishesabout1.77articleequivalentsperyear.Incontrasttotheothermajorfields,postdoc fellowshavehigherpublicationratethantheassociateprofessors,with1.53and1.44articleequivalents,respectively.PhD studentshaveonaverage0.96articleequivalentsperyear.Forallacademicpositions,menhaveslightlyhigherpublication ratethantheirfemalecolleagues,onaverage0.25publicationsperpersonperyear.

PublicationrateversusageforresearchersinthesocialsciencesisshowninFig.8.Overall,thepublicationrateshows alesssteepincreasebyagecomparedwiththehardsciences,butmaleresearchershavehigherpublicationratethantheir femalecolleaguesatthesameage,exceptforattheendoftheircareer.

3.5. Analysisofhumanities

Scholarsinthehumanitieshaveoverallhigherpublicationratethanresearchpersonnelinalltheothermajorfields(see Fig.1).Onaverage,aresearcherwithinthisfieldproduces2.02articleequivalentsperyear,whichistwiceasmuchasthe averageforthewholepopulationofallfields.Themainreasonisadifferentpublicationpattern,whichhassimilaritiesto theonefoundforthesocialsciences,albeitwithanevenhigherproportionofmonographs.Thepublicationrateversusage forresearchersinthehumanitiesisshowninFig.9.

Maleprofessorspublishonaverage2.39articleequivalentsperyear,andhavehigherpublicationratethantheirfemale colleagues,whohaveanaverageoutputof2.08articleequivalentsperyear.Maleprofessorspublishonaverage2.52article equivalentsperyear,andhavehigherpublicationratethantheirfemalecolleagues,whohaveanaverageoutputof2.08 articleequivalentsperyear(Table9).MalePhDstudentsarealsoslightlymoreproductivethanfemales,butforassociate professorsandpostdocs,thegenderdifferenceisminor.

Thepublicationratepatternasafunctionofageandgendershowsthatmaleresearchershavehigherpublicationrate thantheirfemalecolleaguesforallagegroupsexceptintheirearlyforties.Overall,thepublicationrateincreasesbyage,but therelationshipisnotlinear,andthecurvehasseveralpeaks.

Fig.9. Articleequivalents(mean)byagegroupsinthehumanities(N=3691).

3.6. Regressionanalysis–comparativeperspectives

Theregressionanalysisshowsthatthevariableshavedifferentinfluenceontheaveragepublicationratewhencomparing fields.Whileageseemstobeanimportantvariableinbothtechnologyandmedicine,itdoesnothavethesameimportance innaturalsciences,comparedtotheothervariablesanalysed.Thepublicationratedifferencebetweenmaleandfemaleis howeversignificantforthethreementionedfield,withthelargestgenderdifferencesinnaturalsciencesandthelowestin medicine.Innaturalsciences,ageisnotsignificantwhilegenderaccountsfor22percentofthepublicationratedifference betweenmaleandfemalescientists,whenallothervariablesareconstant.Thepublicationratedifferencebetweengender inengineeringandtechnologyis15percentinfavourofmen.Forascientistintechnology,a5-yearageinterval,accounts for12percenthigherpublicationoutput,onaverage.Inthemedicalfield,thedifferenceinpublicationrateisrathersmall betweenmenandwomen,withonly8percentinfavourofmen.Getting5yearsolderwillhowever,accountforabout17 percentinincreasedpublicationoutput,onaverage.

Ifwelookatthepublicationratedifferencesbetweenprofessorsandassociateprofessors,itisaboutthesameforthe threemajorfields(B-coefficients around0.31–0.33)equalstoaround35–40percentinfavourofprofessors.Associate professorspublishagain,morethantheirlessexperiencedcolleagueswhoareinpostdoc-positions,andthedifferenceis almostidenticalforthenaturalsciencesandengineeringandtechnology(B=−0.44i.e.35percentless)whileitisabitless inmedicine(B=−0.35i.e.30percent).ThepublicationratedifferencesbetweenPhDstudentandassociateprofessorsare largeracrossthefields.Thelargestdifferenceisfoundinnaturalsciences(B=−0.66equalsto48percent)whileitissmallest inengineeringandtechnology(B=−0.43equalstoabout35percent).

Intheacademicsystem,thereisahierarchywhereonestartsasaPhDstudentandendupasprofessor.Thismeans thatthetwoexplanatoryvariablesacademicpositionandagemaybehighlycorrelatedwitheachother(collinearity).In theanalysis,particularattentionhasbeendirectedtowardsthispotentialproblem.Table13showstheagedistribution inpercentforeachacademicposition.Table14showsthecorrelationbetweeneachofthevariables.Thelargestpositive correlationisbetweenageandprofessorswiththevalueof0.6,whilethecorrelationbetweenageandPhDstudentsis equallyassociatednegatively.Notsurprisingly,theyoungerresearchersaremainlyholdingjuniorpositionssuchasPhD andpostdocfellowships,whiletheelderandmoreexperiencedresearchersareassociateandfullprofessors.However,the researchersineachoftheacademicpositionsareincludedinseveralagegroups(forexample,professorsinagegroups from30to70years,andPhDstudentsfrom20to50years).Forthisreason,wehaveincludeageasanexplanatoryvariable intheregressionstobeabletomeasuretheeffectofthisvariablewithineachoftheacademicpositions.Inaddition,new regressionswithoutageandagesquaredwereconductedforeachofthethreemajorfields.Ifwecomparethenewregression resultswiththeresultswhereageandagesquaredwereincludedintheregressions,wefindonlyminordifferences.The standarderrorsforeachofthepositionvariablesremainedatthesamelevel,andtheexplainedvariance(R-squared)slightly droppedwhenageandagesquaredwereexcluded.Forexample,inthefieldmedicine,theregressionanalysiswithoutage andagesquared,resultedinanR-squaredvalueof0.17.Thisindicatesthatincludingageandagesquaredonlycontribute toaminorpartofthepublicationrate.However,theB-coefficientforprofessorsincreasedsignificantlywhenageandage

Thedescriptivestatistics(Tables2,4,6,8and10)showthattherearesevencategories(combinationsofacademicpositions andfields)wherefemaleresearchershave20–32percentlowerpublicationscountsthanmen,sixcategorieswherethe publicationcountsare10–20percentlowerpublicationcounts,andsixcategorieswith0–10percentdifference.Inaddition, therearetwocategorieswithacontrarypatternwherefemaleresearchershaveslightlyhigherpublicationcountsthanmen (2–8percenthigher).ThedeviatingfindingsofvanArensbergenetal.(2012)(cf.Section1)thatyoungfemaleresearchers aremoreproductivethanyoungmaleresearchersdonotfindsupportinourstudy.However,withinanagegroupthegender differencesinpublicationrateareusuallysmallerthanwhenthewholepopulationisanalysed.Thisisduetothefactthat therearerelativelymorewomeninjuniorpositions(Table11).

Alsowhenitcomestopublicationdifferenceswithinthehierarchyofacademicpositionsourresultscorroboratethe findingsofseveralpreviousstudies(seee.g.Aksnesetal.,2011;Allison&Stewart,1974;Kyvik,1991;Tien&Blackburn, 1996).Professorsarethemostprolificpersonnelinallfieldsanalysedandacrossbothgenders.Ourresultsshowthatthe

Table8

Articleequivalents(mean)byacademicpositionandgenderinsocialsciences(N=5821).

Academicposition Women Men Bothgenders Diff.,men−women

Professors 1.72 1.79 1.77 0.07

Associateprofessors 1.38 1.49 1.44 0.10

Postdocs 1.45 1.65 1.53 0.20

PhDstudents 0.81 1.11 0.96 0.30

Total/average 1.35 1.60 1.51 0.25

Table9

Articleequivalents(mean)byacademicpositionandgenderinhumanities(N=3691).

Academicposition Women Men Bothgenders Diff.,men−women

Professors 2.08 2.52 2.39 0.44

Associateprofessors 1.83 1.92 1.88 0.09

Postdocs 1.85 1.94 1.89 0.08

PhDstudents 1.12 1.31 1.22 0.19

Total/average 1.79 2.17 2.02 0.38

Table10

Regressionsummaryfornaturalsciences,engineeringandtechnologyandmedicine.

B-coefficients Naturalsciences Engineeringandtechnology Medicine

Variables

Agegroup −0.02 0.12 0.15

Agegroupsquared 0.00 −0.01 −0.01

Gender −0.25 −0.17 −0.08

Professors 0.33 0.31 0.31

Associateprofessorsref.

Postdocs −0.44 −0.44 −0.35

PhDstudent −0.66 −0.43 −0.59

Physicians −0.40

R-squared 0.13 0.15 0.19

Intermsofpublicationfrequency,ourstudyhasrevealedquitelargeagedifferences.Thepublicationrateincreaseswith time,typicallytotheageof40–50inthefieldsanalysed.

AsdescribedinSection1,severalpreviousstudieshaveidentifiedaninvertedU-shapedpublicationpattern(e.g.Cole, 1979;Costas,vanLeeuwen,&Bordons,2010;Fox,1983).Onepreviousstudy(Diem&Wolter,2013)foundthatbothphysical ageandacademicage(i.e.yearsafterobtainingaPhDdegree)haveaneffectonpublicationrate.

Is some of the field analysed we also findan age-related rise and decline pattern. This is most distinct in engi- neering and technology (Fig. 6).However, there are also fields where the publication rate does not decline for the oldestpersonnel(e.g.thesocialsciences, Fig.8).Thismeansthatwecannotinterpretagedeclineasageneralfinding of ourstudy.Withinthe scopeofthis article,we arenot abletodiscuss possiblereasonsfor thepatternsidentified, but various theorieshavebeen developedboth to explaingender andage differencesin productivity(see e.g.Kyvik, 1991).

Scientificpublicationrateisstronglyskewedatthelevelofindividuals:thisholdsforallfields,positionsandagegroups.

Ourstudyhasshownthatpublicationrateintermsofarticleequivalentscanbeexpressedasafunctionofgender,age,age squaredandacademicpositioninallthefieldsinvestigated(thenaturalsciences,engineeringandtechnology,andmedicine).

Theamountthesevariablescanaccountforthechangeinpublicationrate,variesfrom13.5percentfornaturalsciences, 15percentforengineeringandtechnologyand19percentformedicine.Thisshowsthatourmodelshavereasonable explanatorypower.Wehavefoundthatageandacademicpositionaremoreimportantthangenderstatistically,thoughall variablesaresignificant.

Intheanalysis,wehave focusedonthreevariablesthathave beenshowntobeimportantinpreviousstudies.The datamaterialconsistsofresearchersoffourdifferentNorwegianuniversities.However,wedidnotincludeinstitutionasa variable.Astheselecteduniversitiesdonotdifferintermsofworkingconditionsandtimeavailabletospendonresearch, wedidnotexpectanysignificantdifferencesbetweentheinstitutionsintermsofpublicationrate.Inasecondregression analysis,wedidincludeinstitutionasavariabletocontrolfororganisationaldifferencesintermsofpublicationrate.This secondanalysisshowednooronlyminor,improvementstoourmodels.

Althoughtherearenooveralldifferencesatinstitutionallevelwhenitcomestoworkingconditionsandtimeavail- able forresearch,there areimportant variationsat thelevel ofpositions. NorwegianR&D statistics alsoinclude data ontimeavailableforresearch,accordingtoacademicpositions,institutions,anddomains(R&Dequivalents).Thesedata showthattenuredpersonneltendtohave∼40 percentoftheirtimetospendonresearch,whilethefiguresforPhD students andpostdocsarearound70–80per cent.These differencesaremainlydue tothefact thatthetenuredper- sonnelhave muchgreaterteaching obligations.Ifwehad appliedtheR&D equivalentsonthepublicationdatainour study,thedifferencesinthepublicationratelevelsacrossgroupsofacademicpersonnelwouldhavebeenevenlarger.

On theotherhand,itis notuncommonthatPhD students andpostdocscarry outmuch thetime consumingempiri- calinvestigations(e.g.laboratoryandfield work)whilethetenuredscientificstaffaremanagingtheproject.Withina researchgroupledbyaprofessor,theprofessorwilltypicallygether/hisnameonallpublicationsproducedbythegroup, whilethePhDstudentsandpostdocswillbeauthorsonlyinthepublicationstheyhavebeendirectlyinvolvedin(Kyvik, 1991).

Itcanbeconcludedthatmostofthevarianceinpublicationrateattheindividuallevelisduetootherfactorsthanthose investigated.Previousstudieshavesuggestedthatpublicationratealsodependsonawiderangeoffactorsthatcannoteasily bemeasured,suchas:theavailabilityofresearchfunds;teachingloads;equipment;researchassistants;workloadpolicies;

departmentalcultureandworkingconditions;organisationalcontext;andtalentandhardwork(seee.g.Dundar&Lewis, 1998;Kyvik,1993;Ramesh&Singh,1998).Moreover,theprocessofcumulativeadvantage(Merton,1968)impliesthat minordifferencesearlyinacareermayresultinsubstantialdifferencesinachievementbytheendofacareer.Successin scientificcareersmaydependontheabilityofthescientiststhemselvesbutalsoonluck(cf.thedistinctionbetweenvirtu andfortunabyTurner&Chubin,1979).Publicationratestudiesatanindividuallevelthatdonottakeallfactorsintoaccount canthereforeonlyshowpartofthepicture.

Acknowledgements

TheauthorswouldliketothanktwoanonymousreviewersandPålBøringatNIFUfortheirvaluablecommentsona previousdraft.Preliminaryresultsfromthisstudywerepresentedatthe18thInternationalConferenceonScienceand TechnologyIndicators,Berlin(Rørstad&Aksnes,2013).

Annex.

SeeTables11–15andFig.10.

DensitychartsofthelogarithmicofthepublicationoutputindicatorforeachmajorfieldareshowninFig.10.

Professor 428 3501 3929

Associateprofessor 323 1067 1390

Postdoc 505 1244 1749

PhDstudent 810 1680 2490

Engineeringandtechnology 849 3905 4754

Professor 118 1378 1496

Associateprofessor 64 329 393

Postdoc 163 532 695

PhDstudent 504 1666 2170

Medicine 4645 7329 11,974

Professor 719 2463 3182

Associateprofessor 511 446 957

Postdoc 743 640 1383

PhDstudent 1926 1171 3097

Physician/medicaldoctor 746 2609 3355

Total 11,234 24,564 35,798

Table12

Numbersofobservations(articleequivalents)byfieldsandagegroups(N=35,798).

Fieldofsciences 20–24 25–29 30–34 35–39 40–44 45–49 50–54 55–59 60–64 65–69 Morethan70 Total

Humanities 100 355 497 449 424 429 477 516 372 72 3691

Naturalsciences 33 1222 1964 1311 929 963 918 776 709 524 209 9558

Medicine 15 694 1682 1547 1360 1422 1569 1470 1268 708 239 11,974

Socialsciences 3 194 685 749 686 730 787 753 690 435 109 5821

Engineeringandtechnology 25 1069 1306 552 462 337 310 232 248 169 44 4754

Total 76 3279 5992 4656 3886 3876 4013 3708 3431 2208 673 35,798

Table13

Distributionofobservationsbyacademicpositionsandagegroups,percentbyagegroup(N=35,798).

Academicposition 20–24 25–29 30–34 35–39 40–44 45–49 50–54 55–59 60–64 65–69 Morethan70

Professors 0 0 0 3 8 15 19 19 19 13 4

Associatedprof 0 0 6 18 20 17 13 11 8 5 1

Postdoc 0 5 38 34 14 5 2 1 0 0 0

PhD 1 32 39 15 7 3 2 1 0 0 0

Physicians 0 1 4 9 13 16 17 17 14 6 2

Total 0 9 17 13 11 11 11 10 10 6 2

Table14 Correlationmatrix.

Publicationoutput Agegroup Agegroupsquared Gender Professor Assprof Postdoc Physicians Publicationouput 1.00

Agegroup 0.25 1.00

Agegroupsquared 0.24 0.99 1.00

Gender −0.01 −0.16 −0.17 1.00

Professors 0.33 0.61 0.61 −0.20 1.00

Assprof 0.11 0.06 0.06 0.06 −0.31 1.00

Postdoc −0.08 −0.28 −0.28 0.08 −0.30 −0.16 1.00

Physicians −0.19 0.15 0.15 −0.06 −0.24 −0.13 −0.13 1.00

PhD −0.27 −0.60 −0.60 0.15 −0.45 −0.13 −0.23 −0.19

K.Rørstad,D.W.Aksnes/JournalofInformetrics9(2015)317–333331

Professors 2 8 19 25 80 74 124 81 207 90 250 125 294 95 204 14 48 1740

Associateprof 1 9 27 76 103 97 94 85 105 61 65 58 75 34 63 33 40 6 4 1036

Postdoc 1 2 25 37 90 75 63 45 13 10 7 4 1 3 376

PhD 43 53 118 137 61 65 28 17 10 3 3 1 539

Socialsciences 1 2 93 101 317 368 352 397 296 390 274 456 286 501 270 483 222 468 103 332 26 83 5821

Professors 4 7 8 48 46 145 106 272 154 380 171 388 168 397 84 290 23 79 2770

Associateprof 2 25 34 92 136 129 174 109 162 95 106 83 88 52 66 19 42 3 4 1421

Postdoc 3 3 58 74 113 93 67 36 28 6 21 8 7 4 2 2 525

PhD 1 2 88 98 230 253 139 120 54 35 31 16 16 7 9 3 3 1105

Naturalsciences 9 24 410 812 581 1383 358 953 184 745 174 789 152 766 92 684 47 662 46 478 13 196 9558

Professors 3 3 13 14 115 59 366 109 591 100 642 62 582 35 590 37 426 9 173 3929

Associateprof 2 1 13 30 99 77 262 70 195 44 136 47 115 29 98 12 72 9 52 4 23 1390

Postdoc 1 38 86 221 571 191 415 37 126 13 42 3 4 1 1749

PhD 8 22 371 710 327 700 76 161 18 58 8 20 2 5 4 2490

Engineeringandtechnology 3 22 247 822 285 1021 124 428 79 383 49 288 27 283 14 218 15 233 6 163 44 4754

Professors 1 10 11 90 29 203 31 200 16 252 10 203 14 222 6 154 44 1496

Associateprof 2 21 36 8 74 14 94 9 63 7 25 4 15 1 11 9 393

Postdoc 8 52 82 299 48 121 20 44 5 12 4 695

PhD 3 22 239 768 181 676 57 143 16 42 4 13 4 2 2170

Medicalandhealthsciences 7 8 401 293 957 725 803 744 647 713 585 837 536 1033 350 1120 247 1021 94 614 18 221 11974

Professors 1 2 5 23 55 94 134 268 158 454 150 543 132 544 72 397 12 138 3182

Associateprof 1 17 18 57 74 104 94 91 61 106 74 58 62 67 34 8 23 3 5 957

Postdoc 16 14 234 208 262 220 119 102 57 60 35 24 16 6 3 5 1 1 1383

PhD 6 6 373 251 662 413 378 239 236 126 147 74 98 37 25 24 1 1 3097

Physicians 1 2 12 27 43 84 101 188 133 297 156 374 139 444 101 485 44 437 13 193 3 78 3355

Total 20 56 1195 2084 2292 3700 1872 2784 1419 2467 1264 2612 1153 2860 875 2833 690 2741 377 1831 77 596 35798

Fig.10. Densitychartslog(articleequivalents)ofallmajorfieldsseparatelyandforallfields.