A long-term assessment of the multidisciplinary degree of multidisciplinary journals

RESEARCH ARTICLE A long- e m assessmen o he mul idisciplina y deg ee o mul idisciplina y jou nals Daniel Redondo-Go ´mezID 1 *, Wenceslao A oyo-Machado 2 , Daniel To es-Salinas 2 , An oni Ma galida 3,4 , Ma cos Moleo ´n 1 1Depa men o Zoology, Uni e si y o G anada, G anada, Spain, 2Depa men o In o ma ion and Communica ion Sciences, Uni e si y o G anada, G anada, Spain, 3Ins i u e o Game and Wildli e Resea ch, IREC (CSIC-UCLM), Ciudad Real, Spain, 4Py enean Ins i u e o Ecology (CSIC), Jaca, Spain *[email p o ec ed] Abs ac A e mul idisciplina y jou nals uly mul idisciplina y, and, how has he mul idisciplina y cha - ac e o hese jou nals e ol ed o e he long e m? He e, we assess hese ques ions by analyzing da a om he Jou nal Ci a ion Repo s. We examined 983,246 a icles and e iews published be ween 1980 and 2021 in 127 jou nals ca ego ized unde ‘Mul idisciplin- a y Sciences’. We ound ha he ep esen a ion o he main b anches o knowledge in mul i- disciplina y jou nals was une en and, in gene al, no p opo ional o he global esea ch e o dedica ed o each b anch. Simila ly, he dis ibu ion o publica ions ac oss speci ic esea ch a eas was une en, wi h “Biochemis y & Molecula Biology” s ongly o e ep e- sen ed. Howe e , we de ec ed a dec easing end in he pe cen age o publica ions ha mul- idisciplina y jou nals dedica e o his and o he op a eas, especially o e he las decade. The mul idisciplina y deg ee o mul idisciplina y jou nals, as measu ed by he Gini index, was gene ally low bu showed a g adual inc ease o e ime. The impac ac o o mul idisci- plina y jou nals was posi i ely ela ed o he pe cen age o publica ions in he a ea “Bio- chemis y & Molecula Biology”. Compa ed o o he mul idisciplina y jou nals, Na u e, Science, and PNAS emphasized his a ea e en mo e s ongly, hough he di e ence be ween he i s - anked a ea and he o he op a eas consis en ly dec eased since 1980. In conclusion, while a s ong bias emains in a o o highly ci able a eas, mul idisciplina y jou - nals a e p og essi ely inc easing hei deg ee o mul idisciplina i y in ecen yea s. Thus, we encou age au ho s o ca e ully conside his pola iza ion when selec ing jou nals o hei s udies, and we sugges ha scien i ic agencies keep i in mind when e alua ing esea che s. In oduc ion Mul idisciplina y jou nals, i.e., hose lis ed in he Jou nal Ci a ion Repo s (JCR) unde he ca - ego y ‘Mul idisciplina y Sciences’ o in Scopus wi hin he subjec a ea ‘Mul idisciplina y’, a e PLOS ONE PLOS ONE | h ps://doi.o g/10.1371/jou nal.pone.0314616 Decembe 2, 2024 1 / 15 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Ci a ion: Redondo-Go ´mez D, A oyo-Machado W, To es-Salinas D, Ma galida A, Moleo ´n M (2024) A long- e m assessmen o he mul idisciplina y deg ee o mul idisciplina y jou nals. PLoS ONE 19(12): e0314616. h ps://doi.o g/10.1371/jou nal. pone.0314616 Edi o : Robin Haunschild, Max Planck Ins i u e o Solid S a e Resea ch, GERMANY Recei ed: Decembe 11, 2023 Accep ed: No embe 13, 2024 Published: Decembe 2, 2024 Pee Re iew His o y: PLOS ecognizes he bene i s o anspa ency in he pee e iew p ocess; he e o e, we enable he publica ion o all o he con en o pee e iew and au ho esponses alongside inal, published a icles. The edi o ial his o y o his a icle is a ailable he e: h ps://doi.o g/10.1371/jou nal.pone.0314616 Copy igh : ©2024 Redondo-Go ´mez e al. This is an open access a icle dis ibu ed unde he e ms o he C ea i e Commons A ibu ion License, which pe mi s un es ic ed use, dis ibu ion, and ep oduc ion in any medium, p o ided he o iginal au ho and sou ce a e c edi ed. Da a A ailabili y S a emen : Da a can be ound in h ps://doi.o g/10.5281/zenodo.13269363. Funding: DRG was unded by a p edoc o al g an om he Jun a de Andalucı ´a (PREDOC_00262). supposed o accommoda e he publica ion o esea ch pape s om a ious a eas o esea ch o disciplines. Bu , o wha ex en a e hese jou nals ac ually mul idisciplina y? In hese jou nals, mul idisciplina i y may be achie ed h ough wo ways: by including mul idisciplina y publica- ions and by ga he ing unidisciplina y publica ions om mul iple disciplines. Howe e , mul i- disciplina y jou nals o en publish a small p opo ion o uly mul idisciplina y a icles [1] and a e g ea ly biased owa ds ce ain disciplines [2,3]. In pa icula , mul idisciplina y jou nals usually end o accep a icles based on hei po en ial ci abili y [4,5]. Thus, he mul idiscipli- na i y o hese jou nals may be comp omised by os e ing a ew a eas cha ac e ized by high- impac scien i ic p oduc ion [3] o he de imen o less ci ed a eas. Though mul idisciplina y jou nals ha e been p o usely analyzed in he scien i ic biblio- me ic li e a u e, mos esea ch has been ocused on e y speci ic issues o only on a ew op jou nals [2,3,6]. The inc ease in he mul idisciplina i y o se e al speci ic a eas is well docu- men ed (such as medicine [7]; cogni i e science [8]; nanoscience and nano echnology [9]; and o he s [10]) bu li le is known abou how he mul idisciplina y cha ac e o mul idisciplina y jou nals has changed o e ime. Despi e his end in speci ic a eas, he g owing compe i i e- ness o he inc easingly c owded mul idisciplina y ca ego y may jeopa dize i s mul idisciplin- a y na u e, since i is expec ed ha jou nals use all possible esou ces o become and emain as high as possible in he impac and ci a ion ankings [4]. He e, we aim o explo e how he mul idisciplina y cha ac e o mul idisciplina y jou nals has changed in he long e m. Fo his gene al pu pose, we ha e delinea ed i e main speci ic goals a h ee le els. Fi s , a he le el o he ‘Mul idisciplina y Sciences’ ca ego y, we aim i) o de e mine i he ep esen a ion o he di e en b anches and a eas o knowledge in mul idisci- plina y jou nals is p opo ional o he null expec a ions indica ing mul idisciplina i y. Ou null expec a ions a e: a) mul idisciplina y jou nals alloca e he same space (i.e. simila p opo - ion o i ems published) o each b anch/a ea, and b) he space alloca ed in mul idisciplina y jou nals o each b anch/a ea is p opo ional o he global esea ch e o behind each b anch/ a ea. Also, we aim ii) o iden i y he a eas o knowledge ha ha e been o e ep esen ed in mul- idisciplina y jou nals, and i hey ha e changed o e he las ou decades. Second, a he le el o all mul idisciplina y jou nals, we aim iii) o assess which jou nals a e mo e mul idisciplina y and i hey ha e changed o e ime. Also, we aim i ) o in es iga e i a) he mul idisciplina i y deg ee o he jou nal and b) he p opo ion o publica ions in he jou nal ha belong o he op a ea (acco ding o he numbe o a icles) a e ela ed o he impac ac o o mul idisciplin- a y jou nals. Thi d, wi h a ocus on he h ee op mul idisciplina y jou nals (Na u e,Science, and P oceedings o he Na ional Academy o Sciences,PNAS), we aim ) o es ablish which o hem is ad ancing he mos owa d mul idisciplina i y. Ma e ials and me hods Web o Science ca ego ies Web o Science and InCi es ha e di e en classi ica ion schemas o he esea ch ca ego ies o scien i ic jou nals, wi h he ca ego ies o Web o Science being he mos used. This scheme, comp ising a o al o 254 ca ego ies, is used o classi y he jou nals indexed in he Jou nal Ci a- ion Repo s (JCR). These jou nals can be assigned up o six ca ego ies based on c i e ia such as hema ic alignmen , au ho and ins i u ion a ilia ions, ci a ions and e e ences (h ps:// suppo .cla i a e.com/Scien i icandAcademicResea ch/s/a icle/Web-o -Science-Co e- Collec ion-Web-o -Science-Ca ego ies?language=en_US). Addi ionally, hese ca ego ies a e hen inhe i ed by he a icles published in hem. Howe e , he e is an excep ion o he ca ego- ies “Mul idisciplina y Sciences” and “Medicine, Gene al, and In e nal”. Thei a icles a e eassigned h ough an algo i hmic p ocess based on hei e e ences o o he hema ic a eas, PLOS ONE A long- e m assessmen o he mul idisciplina y deg ee o mul idisciplina y jou nals PLOS ONE | h ps://doi.o g/10.1371/jou nal.pone.0314616 Decembe 2, 2024 2 / 15 WAM was unded by FPU G an (FPU18/05835) om he Spanish Minis y o Uni e si ies. MM was pa ly suppo ed by he Se e o Ochoa P og am o Cen es o Excellence in R+D+I (SEV-2012-0262) and by a esea ch con ac Ramo ´n y Cajal om he MINECO (Minis e io de Economı ´a, Indus ia y Compe i i idad; RYC-2015-19231). The unde s had no ole in s udy design, da a collec ion and analysis, decision o publish, o p epa a ion o he manusc ip . Compe ing in e es s: The au ho s ha e decla ed ha no compe ing in e es s exis . al hough his is only done in InCi es and no o all publica ions (h ps://inci es.help.cla i a e. com/Con en /Indica o s-Handbook/ih-documen - eclassi ica ion.h m). Da a ga he ing Fi s , we selec ed all jou nals included in he ca ego y “Mul idisciplina y Sciences” o a leas one o he edi ions be ween 1997 and 2020 (n = 127 jou nals; “mul idisciplina y jou nals”), acco ding o da a om he Jou nal Ci a ion Repo s. We excluded ESCI (Eme ging Sou ces Ci a ion Index) jou nals. The jou nals we e indi idualized by ISSN/eISSN, assigning he mos ecen name in case o name changes. O hese jou nals, 55 (43%) we e included in he ca e- go y “Mul idisciplina y Sciences” o a leas hal o he s udy pe iod, and only 10 (8%) we e included o <5 yea s. Also, du ing he s udy pe iod, 86 jou nals (68%) we e exclusi ely ca e- go ized as “Mul idisciplina y Sciences”. Then, we ga he ed all publica ions, i.e., “a icles” and “ e iews” (documen s ha always unde go pee e iew and ecei e he majo i y o he ci a- ions), om hese jou nals be ween 1980 and 2021, a e manually il e ing he jou nals by ISSN in he InCi es publica ion sou ces module and downloading all publica ions ha me he c i e ia o ime and ypology. F om hese publica ions, we eco ded he publica ion da e (yea ), sou ce (publishing jou nal), and esea ch “a ea” (Web o Science ca ego ies; no e ha InCi es algo i hmically eassigns publica ions in mul idisciplina y jou nals o hei mos ele- an a ea, acco dind o hei ci ed e e ences when a ailable). Following A oyo-Machado & To es-Salinas, 2021 [11], we classi ied he cu en 254 esea ch a eas in o six majo “b anches” o knowledge: “Mul idisciplina y”, “A s & Humani ies”, “Li e Sciences & Biomedi- cine”, “Physical Sciences”, “Social Sciences”, and “Technology”. I is impo an o no e ha he “Mul idisciplina y” b anch includes only one a ea (“Mul idisciplina y Sciences”). Second, we ga he ed all publica ions om all JCR jou nals o he same pe iod (1980–2021). F om hese publica ions, we also eco ded he publica ion da e (yea ), sou ce (publishing jou nal), “a ea”, and “b anch”. Da a ea men and analyses: Mul idisciplina y sciences Fo each esea ch a ea, we calcula ed 1) he numbe o publica ions in he esea ch a ea in all mul idisciplina y jou nals each yea , as a measu e o he g oss numbe o publica ions, 2) he a io be ween he pe cen age o publica ions in each esea ch a ea each yea in mul idisciplin- a y jou nals and he pe cen age o publica ions in each esea ch a ea each yea in he wo ld (he ea e , “mul idisciplina y/wo ld a io”), as a measu e o he weigh ed numbe o publica- ions ela i e o he global esea ch e o and 3) he posi ion o he esea ch a ea in he anking o he numbe o publica ions by mul idisciplina y jou nals each yea . Publica ions included in mo e han one esea ch a ea we e conside ed in each o he a eas hey we e included (bu no e ha only 3.1% o publica ions we e included in mo e han one a ea, and ha hese mul i- ple a eas we e o en closely ela ed, e.g., “Compu e Science, Ha dwa e & A chi ec u e” and “Compu e Science, Theo y & Me hods”). To es ou null expec a ions indica ing mul idisci- plina i y, we pe o med Chi-squa ed analyses compa ing, o he en i e s udy pe iod and excluding he b anch “Mul idisciplina y Sciences”, he median pe cen age o a icles published in each b anch in mul idisciplina y jou nals and a) a balanced pe cen age (i.e., 20% o o al publica ions belonging o each o he i e b anches) and b) he pe cen age o a icles published in each b anch in he wo ld (i.e., in all jou nals excep hose included in he a ea “Mul idisci- plina y Sciences"). To explo e in e -annual ends, we made Pea son co ela ions be ween he yea and he yea ly pe cen age o publica ions ha mul idisciplina y jou nals de o e o a) he op-30 a eas o knowledge (acco ding o he o al numbe o publica ions) and b) he a ea “Biochemis y & Molecula Biology”. PLOS ONE A long- e m assessmen o he mul idisciplina y deg ee o mul idisciplina y jou nals PLOS ONE | h ps://doi.o g/10.1371/jou nal.pone.0314616 Decembe 2, 2024 3 / 15 Da a ea men and analyses: Mul idisciplina y jou nals Simila ly, o all mul idisciplina y jou nals (i.e., n = 127 jou nals wi hin he a ea “Mul idisci- plina y Sciences"), we calcula ed 1) he numbe o publica ions in each esea ch a ea each yea , 2) he a io be ween he numbe o publica ions in he jou nal and he wo ld numbe o publi- ca ions in each esea ch a ea each yea (he ea e jou nal/wo ld a io), and 3) he “Mul idisci- plina i y deg ee” ( om he Gini index) [12,13]. This inequali y index anges be ween 0 (all esea ch a eas a e equally ep esen ed i.e., hey ha e he same numbe o publica ions) and 1 (all publica ions a e concen a ed in one esea ch a ea). The Gini index was compu ed using he unc ion ineq() om he ineq package [14]. The mul idisciplina i y deg ee was calcula ed as 1—Gini index. Addi ionally, we made Pea son co ela ions be ween he yea ly impac ac o o mul idisciplina y jou nals (acco ding o Web o Science da a) and a) hei yea ly mul idisci- plina i y deg ee and b) he yea ly pe cen age o publica ions belonging o he op- anked esea ch a ea: “Biochemis y & Molecula Biology”. Also, we co ela ed he yea ly pe cen age o publica ions belonging o “Biochemis y & Molecula Biology” wi h he yea ly mul idiscipli- na i y deg ee. To de ec empo a y ends, we made addi ional Pea son co ela ions be ween he yea ly pe cen age o publica ions belonging o “Biochemis y & Molecula Biology”, he pe cen age o publica ions in he op-30 a eas (acco ding o he numbe o a icles and exclud- ing “Mul idisciplina y Sciences”) and he yea (as a p oxy o ime). All s a is ical analyses we e conduc ed in R 4.0.5 [15]. Da a ea men and analyses: Top mul idisciplina y jou nals The wo ld’s h ee mos in luen ial mul idisciplina y jou nals: Na u e,Science, and PNAS we e analyzed in de ail. As o he es o he jou nals, we calcula ed 1) he numbe o publica ions in each esea ch a ea each yea , 2) he jou nal/wo ld a io, and 3) he “Mul idisciplina i y deg ee” om he Gini index, as well as he empo al changes o hese a iables h oughou he s udy pe iod. To de ec empo a y ends, we also made Pea son co ela ions be ween he yea ly pe cen age o publica ions belonging o “Biochemis y & Molecula Biology”, he pe - cen age o publica ions in he op-30 a eas (acco ding o he numbe o a icles and excluding “Mul idisciplina y Sciences”) and he yea (as a p oxy o ime). Resul s Rela i e ole o esea ch b anches and a eas in he ‘Mul idisciplina y Sciences’ ca ego y Ou bibliog aphic dump o he ‘Mul idisciplina y Sciences’ ca ego y included 127 jou nals ha published a o al o 983,246 a icles and e iews (he ea e “publica ions”) be ween 1980 and 2021 (S1 Table). Mo e han hal o hese publica ions (604,578 publica ions; 61.5% o he o al) belonged o he b anch o knowledge “Li e Sciences & Biomedicine”, ollowed by “Physi- cal Sciences” (152,629 publica ions; 15.5%; S1 Table). The b anch wi h he lowes ep esen a- ion was “A s & Humani ies” (6,124 publica ions; 0.6%; S1 Table). The dis ibu ion o publica ions by b anches o knowledge in mul idisciplina y jou nals was clea ly une en, ei he o he en i e s udy pe iod (χ 2 = 40.51, p <0.001 in he Chi-squa ed es compa ing he median pe cen age o publica ions published in each b anch and he balanced pe cen age, i.e., 20% o each o he i e b anches, excluding “Mul idisciplina y Sciences”) o sepa a ely by decades (χ 2 = 37.78–47.32, p <0.001 o all cases). In addi ion, we ound di e ences be ween he median pe cen age o a icles published in each b anch in mul idisciplina y jou nals wi h espec o he median pe cen age o a icles published in each b anch in he wo ld, o he en i e pe iod (χ 2 = 15.15, p <0.01) and o 1980–1989 (χ 2 = 14.89, p <0.01), 2010–2019 (χ 2 = PLOS ONE A long- e m assessmen o he mul idisciplina y deg ee o mul idisciplina y jou nals PLOS ONE | h ps://doi.o g/10.1371/jou nal.pone.0314616 Decembe 2, 2024 4 / 15 23.23, p <0.001) and 2020–2021 (χ 2 = 14.70, p <0.01), bu no o 1990–1999 (χ 2 = 8.24, p = 0.083) and 2000–2009 (χ 2 = 6.85, p = 0.144). Since 1980, he ela i e con ibu ion o he b anch "Mul idisciplina y" o mul idisciplina y esea ch has been dec easing in a o o "Li e Sciences & Biomedicine", while he ela i e con ibu ion o he es o he b anches o knowl- edge has emained app oxima ely s able (Fig 1). Wi h ega ds o he esea ch a eas (Fig 2), he 30 a eas wi h he highes numbe o publica- ions belonged o he b anches “Mul idisciplina y Sciences” (no e ha he e is only one a ea wi hin his b anch), “Li e Sciences & Biomedicine” (43.3% o he 30 a eas), “Physical Sciences” (40.0%), “Technology” (10.0%) and “A s and Humani ies” (3.3%; he e was none esea ch a ea belonging o he b anch “Social Sciences” wi hin hese 30 a eas). “Mul idisciplina y Sci- ences” and “Biochemis y & Molecula Biology” we e he wo a eas wi h mo e publica ions pe yea in mul idisciplina y jou nals (12.0% and 13.1% as a e age o o al publica ions in mul- idisciplina y jou nals, espec i ely; Fig 2B). These a eas we e ollowed by o he a eas belong- ing o he b anches o knowledge “Li e Sciences & Biomedicine” and “Physical Sciences”, such as “Ecology”, “Neu osciences”, “Immunology”, “Ma hema ics”, “Geochemis y & Geophysics” and “Cell Biology”. Wi hin he b anch “Technology”, he esea ch a eas o “Enginee ing, Mul- idisciplina y” and “Ma e ials Science, Mul idisciplina y” we e he wo a eas wi h mo e publi- ca ions. Wi hin he b anch “A s and Humani ies”, “His o y & Philosophy o Science” was he only esea ch a ea among he 30 a eas wi h mo e publica ions. O e all, we de ec ed a s ong imbalance among a eas, as he numbe o publica ions ela ing o he i s i e op a eas was simila o he o al numbe o publica ions ela ing o all he emaining a eas in he op 30 (median = 29,297 publica ions, co esponding o he i h a ea “Immunology”). Mo eo e , he a e age yea ly numbe o publica ions belonging o “Biochemis y & Molecula Biology” (3058 publica ions, ange = 1401–7381, 13.1%) was ma kedly highe han he a e age yea ly numbe o publica ions belonging o each o he o he i s 30 a eas excluding “Mul idisciplin- a y Sciences” (395 publica ions, ange = 66–1543, 0.3%). In gene al, he pe cen age o publica- ions ha mul idisciplina y jou nals de o ed o hese op-30 a eas has inc eased since 1980 ( = 0.798, p <0.001), al hough his end was e e sed since 2011 (S1 Fig). In he case o he a ea “Biochemis y & Molecula Biology”, i s pe cen age in mul idisciplina y jou nals has been Fig 1. Decadal e olu ion o he pe cen age o publica ions (“a icles” and “ e iews”) pe b anch o knowledge in mul idisciplina y jou nals (acco ding o he Web o Science) om 1980 o 2021. h ps://doi.o g/10.1371/jou nal.pone.0314616.g001 PLOS ONE A long- e m assessmen o he mul idisciplina y deg ee o mul idisciplina y jou nals PLOS ONE | h ps://doi.o g/10.1371/jou nal.pone.0314616 Decembe 2, 2024 5 / 15 Fig 2. a) Posi ion o each esea ch a ea in he anking o he numbe o publica ions in mul idisciplina y jou nals pe yea . Numbe one in he y axis ep esen s he esea ch a ea wi h mo e publica ions. G aph a) ep esen s he comple e g aph including all he esea ch a eas and he g aph c) is he enla ged pa indica ed by he squa e (wi h he axes in e ed). b) Numbe o publica ions o each esea ch a ea in mul idisciplina y jou nals pe yea . Only he i s 30 esea ch a eas o each g aph a e shown, dec easingly so ed by he median. Resea ch a eas a e classi ied by b anches o knowledge and poin s a e colo ed acco ding o yea . h ps://doi.o g/10.1371/jou nal.pone.0314616.g002 PLOS ONE A long- e m assessmen o he mul idisciplina y deg ee o mul idisciplina y jou nals PLOS ONE | h ps://doi.o g/10.1371/jou nal.pone.0314616 Decembe 2, 2024 6 / 15 dec easing since he mid-1980s ( = -0.548, p <0.001; S1 Fig). This dec ease has been pa icu- la ly ma ked in he las decade ( = -0.975, p <0.0001; S1 Fig). When so ing he esea ch a eas by he numbe o publica ions pe yea , we ound ha he op- anked a eas o all yea s du ing he en i e s udy pe iod we e “Biochemis y & Molecula Biology” and “Mul idisciplina y Sciences” (Fig 2A and 2C), excep in 2012, when “Biochemis y & Molecula Biology” and “Neu osciences” we e in he op posi ions. Be o e 1999, “Mul idisciplin- a y Sciences” was always in he i s posi ion ollowed by “Biochemis y & Molecula Biology”, bu , since 2000, hese posi ions became e e sed, excep in 2021, in which “Mul idisciplina y Sci- ences” e u ned o he i s posi ion. The ollowing a eas ha e su e ed mo e in e -annual changes in hei posi ion in he anking, especially as hei median posi ion in he o al anking is lowe . Some a eas showed a clea inc easing end in hei posi ions in he anking, such as “Neu osci- ences”, “Cell Biology” and “Ma e ials Science”, while o he s showed he opposi e end, such as “Geochemis y & Geophysics”, “Geosciences” and “As onomy & As ophysics” (Fig 2C). The o e whelming p imacy o “Mul idisciplina y Sciences” and “Biochemis y & Molecula Biology” was also e iden when plo ing he pe cen age o publica ions o each a ea in mul i- disciplina y jou nals agains he wo ld pe cen age o publica ions o each a ea (Fig 3A and 3B). To a lesse ex en , o he a eas such as "Ecology", "Neu osciences", “Immunology”, “Ma h- ema ics” and “Cell Biology” we e also o e ep esen ed. In con as , o he esea ch a eas such as “Su ge y”, “Enginee ing, Elec ical & Elec onic”, “Chemis y, Mul idisciplina y”, “Physics, Applied” and “Ma e ial Sciences” we e unde ep esen ed (see Fig 3A and 3B). “Vi ology”, “Immunology”, “Neu osciences” and “Cell Biology” consis en ly inc eased hei ep esen a- ion o e ime wi h espec o he wo ld con ex . Besides, o he a eas such as “Biodi e si y Conse a ion”, “Geog aphy, Physical” o “As onomy and As ophysics” ha e los p ominence since 1980 (Fig 3C). How mul idisciplina y a e mul idisciplina y jou nals, and i s ela ion o he jou nal impac Fi s , we assessed which jou nals a e mo e mul idisciplina y by calcula ing hei “Mul idisci- plina i y deg ee” om he Gini index. In gene al, he mul idisciplina i y deg ee was low in all mul idisciplina y jou nals du ing all yea s (<0.25 in all cases; Fig 4). Speci ically, wo hi ds (67.7%) o mul idisciplina y jou nals showed an a e age Gini index highe han 0.95. Royal Socie y Open Science,PLoS ONE,Scien i ic Repo s, and PEERJ we e he jou nals wi h he high- es median mul idisciplina i y deg ee (lowes Gini index). The gene al end o he olde jou - nals was o inc ease hei mul idisciplina i y deg ee o e ime. Na u e,Science, and PNAS appea in he anking posi ions as 19 h, 29 h, and 44 h, espec i ely (Fig 3). The jou nals’ impac ac o was posi i ely ela ed o hei pe cen age o publica ions in he a ea “Biochemis y & Molecula Biology” ( = 0.290, p <0.001; Fig 4C), as well as o hei mul- idisciplina i y deg ee ( = 0.200, p <0.001; Fig 4D). Acco dingly, he e was also a posi i e co - ela ion be ween he pe cen age o publica ions in he a ea “Biochemis y & Molecula Biology” and he mul idisciplina i y deg ee o he jou nals ( = 0.334, p <0.001; Fig 4E). How- e e , his coun e in ui i e co ela ion is condi ioned by a ew alues, and jou nals ha pub- lished many “Biochemis y & Molecula Biology” publica ions showed in gene al e y low mul idisciplina i y deg ees (Fig 4E). In ac , he e we e no jou nals wi h many “Biochemis y & Molecula Biology” publica ions and high mul idisciplina i y deg ee. Mul idisciplina i y in op mul idisciplina y jou nals As obse ed o he whole “Mul idisciplina y Sciences” ca ego y, he numbe o publica ions o he di e en esea ch a eas in he op mul idisciplina y jou nals was highly une en (S2 Fig). PLOS ONE A long- e m assessmen o he mul idisciplina y deg ee o mul idisciplina y jou nals PLOS ONE | h ps://doi.o g/10.1371/jou nal.pone.0314616 Decembe 2, 2024 7 / 15 Fig 3. Rela ion be ween he pe cen age o publica ions o each esea ch a ea in mul idisciplina y jou nals and he pe cen age o publica ions o ha esea ch a ea in he wo ld. G aph b) is a zoom o he indica ed pa o g aph a). Each esea ch a ea is ep esen ed by a colo . The black line ep esen s he 1:1 a io, namely he publica ions in each esea ch a ea in mul idisciplina y jou nals a e p opo ional o he global publica ions in ha a ea. No e he g ea o e ep esen a ion o " Biochemis y & Molecula Biology " in mul idisciplina y jou nals. c) Ra io be ween he pe cen age o publica ions in each PLOS ONE A long- e m assessmen o he mul idisciplina y deg ee o mul idisciplina y jou nals PLOS ONE | h ps://doi.o g/10.1371/jou nal.pone.0314616 Decembe 2, 2024 8 / 15 Howe e , unlike o he “Mul idisciplina y Sciences” ca ego y, “Biochemis y & Molecula Biology” was he esea ch a ea wi h he highes numbe o publica ions in he h ee op mul i- disciplina y jou nals, well abo e “Mul idisciplina y Sciences”, especially in PNAS. In pa icu- la , “Biochemis y & Molecula Biology” ep esen ed 27.2–47.7% o o al publica ions o he op 15 a eas in hese jou nals. We ound ha he numbe o publica ions ela ing o he i s wo op a eas was simila o he o al numbe o a icles ela ing o all he emaining a eas in he op-15 (median = 3395 publica ions, co esponding o he hi d a ea “As onomy and As ophysics” o Na u e; 2755 publica ions, co esponding o he hi d a ea “Neu osciences” o Science; and 6964 publica ions, co esponding o he hi d a ea “Mul idisciplina y Sci- ences” o PNAS). These esul s we e consis en be ween jou nals and o e ime (see S2 Fig). Tha said, he ep esen a ion o “Biochemis y & Molecula Biology” in hese h ee jou nals is consis en ly dec easing since 1980 ( = -0.649, p <0.001 o Na u e; = -0.461, p <0.01 o Science; = -0.988, p <0.001 o PNAS), hough s ill hese jou nals publish mo e han double o publica ions o his a ea compa ed o he a e age o o he mul idisciplina y jou nals. In e sely, he ep esen a ion o he o he op esea ch a eas is inc easing in ecen yea s, espe- cially in PNAS (S2 Fig). Focusing on he 15 a eas wi h he highes numbe o publica ions, mos o he publica ions we e wi hin he b anch o knowledge o “Li e Sciences & Biomedi- cine” (88.6% o PNAS, 57.0% o Na u e and 52.4% o Science), while Na u e and Science also had a la ge numbe o publica ions in “Physical Sciences” (28.0% o Na u e, 29.8% o Science and 4.0% o PNAS;S2 Fig). Compa ing wi h all mul idisciplina y jou nals, he e a e some a eas ha play a no ably mo e (e.g., “As onomy & As ophysics”) and less p ominen ole (e.g., “Ecology” and “Ma hema ics, In e disciplina y Applica ions”) in he h ee op jou nals. Wi h ega ds o he anking o each a ea in he h ee op mul idisciplina y jou nals, we obse e a simila in e -annual pa e n han o all mul idisciplina y jou nals (Fig 2C), hough some di e ences a ise. Fo ins ance, in Na u e, he posi ion in he anking o he op a eas is much mo e s a ic (S3 Fig). When weighing he numbe o publica ions by he wo ld numbe o publica ions in each esea ch a ea, he p ominence o he b anches o knowledge o “Li e Sciences & Biomedicine” and “Physical Sciences” is main ained. In pa icula , “Biochemis y & Molecula Biology” and “Geochemis y & Geophysics” we e esea ch a eas wi h a clea o e - ep esen a ion. Howe e , he e is a ma ked and ubiqui ous endency o educe he o e ep e- sen a ion o op esea ch a eas, especially in Na u e and Science. In addi ion, PNAS shows a clea inc ease in he ep esen a ion o unde ep esen ed a eas (Fig 2C and S4 Fig). Discussion He e, we p esen a comp ehensi e long- e m analysis o he mul idisciplina y cha ac e o mul idisciplina y jou nals. Excluding he “Mul idisciplina y” b anch and he co esponding “Mul idisciplina y Sciences” a ea, which accoun ed o 12% o o al publica ions in hese jou - nals, we obse ed a s ong bias in a o o publica ions wi hin speci ic b anches and a eas o knowledge, consis en wi h indings om p e ious s udies [1–3]. None heless, ou analysis also e eals a ecen end in mul idisciplina y jou nals owa d educing his imbalance. Con a y o ou null expec a ions, we ound ha he ep esen a ion o he i e main b anches o knowledge, namely “Li e Sciences & Biomedicine”, “Physical Sciences”, “Technol- ogy”, “Social Sciences”, and “A s & Humani ies” (in ha o de acco ding o hei numbe o publica ions), in mul idisciplina y jou nals was no ully balanced no , excep o he pe iod 1990–2009, p opo ional o he global esea ch e o dedica ed o each b anch. Thus, esea ch a ea each yea in mul idisciplina y jou nals and he pe cen age o publica ions o each esea ch a ea each yea in he wo ld (mul idisciplina y:wo ld a io). h ps://doi.o g/10.1371/jou nal.pone.0314616.g003 PLOS ONE A long- e m assessmen o he mul idisciplina y deg ee o mul idisciplina y jou nals PLOS ONE | h ps://doi.o g/10.1371/jou nal.pone.0314616 Decembe 2, 2024 9 / 15