JOURNALCITATIONREPORTS

IntroductionI. journals, References,

and Citations

A citation index is baaed on the principle thatthere is some meaningful relationship betweenone paper and some other that it cites or thatcites it, and thus between the work of the twoauthors or two groups of authors who publishedthe papers.

The entire SC/Q data base is stored on mag-netic tape, and it is thus amenable to extensivemanipulation and analysis. In the case of au-thors, we have been able to identify the fre-quency with which they and their papers arecited in the literature, over any chosen timeperiod. Counts of this sort are strictly quantita-tive and objective. But even admitting this limi-tation, an author’s or a paper’s frequency ofcitation has been found to correlate well withprofessional standing. It is certainly not the on/ymeasure, nor one that can be used, for anypurpose, in isolation. We do not claim for it theabsolute reliability that critics of citation analysishave wrongly imputed to us when they haveattacked it. The fact does remain, however, thatit provides a useful objective criterion previouslyunavailable.

Basically the same principle can be used inevaluation of journals, rather than of authors’publications or single papers. When a scientistcites a previously published article, he tells us, ina sense, that he has read it and has some reasonfor bringing it to our attention. The more fre-quently a journal’s articles are cited. the morethe world’s scientific community implies that itfinds the journal to be a carrier of useful infor-mation.

Evsfuaring Journals

It has always been and still remains diftlcult toassess the relative importance of scientific andtechnical journals. There have been few, if any,totally objective criteria by which to measurethem. Researchers and their library colleaguesquickly learn what journals are most ‘important’for particular dkciplines, and countless studieshave been carried out to establish ‘core-journal’lists. But as research interest and activity extend

]eyond the basic discipline, as interdisciplinadmd multidisciplinary ‘mission-oriented’ researchrequires broader journal coverage, the relevatrrxmd usefulness of journals outside the disciplin-my core may be difficult to determine. Evenwithin the small d~ciplinary or departmental li-brary, when a choice between journals is dictatedby restricted acquisitions budgets, considerationsless relevant than scientific merit may all toolikely determine or force the choice--politics,sheer habit, relative subscription cost, and so on.

Thus, the Journal Citation Reporma (JCR” )extends the use of citation analysis to examinethe relationships among journals rather thanamong articles and their authors. The JCR an-swers these basic questions: how often has ajournal been cited? what journals have cited it?how frequently have particular joirrnah cited it?does the cited material in the case of a particularIOUrnal come primarily from older articles, newerarticles, or does the citation pattern show achronological consistency? what journals has theparticular journal itself cited? how often has itcited each of them? is it citing old material, newmaterial? what part of these counts is due toself-citation? in other words: who uses a partic-ular journal? how frequently? for what purposes?

The Total Framework

Like any other tool, the JCR cannot be usedindiscriminately. It is a source of highly valuableinformation, but that information must be usedwithin a total framework proper to the decision tobe made, the hypothesis to be examined, andrarely in isolation without consideration of otherfactors, objective and subjective. For example,there are undoubtedly highly useful journals thatare not cited frequently. Scientists read manysuch journals for the same reason people readnewspapers and other non-scientific periodicals--to keep up with what’s going on generally. Theymay rarely cite such journals in their publishedwork. This does not mean that such uncited orinfrequently cited joumala are any less useful fortheir intended purpose than cited journals. hdoes mean, however, that these journals arewritten and read for a purpose other than thecommunication of original research fmtlngs andthe indispensable summary of research findingsprovided by reviews.

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Another consideration is that citation frequen-cy is sometimes--indeed to some extent must

be--a function of variables other than scientificmerit. Some such variables may be an author’sreputation, the controversiality of subject matter,a journal’s circulation and its cost, reprint dis-semination, its coverage by current-awarenessand indexing and abstracting services, societymemberships, the availability and estent of li-braries’ journal collections, national research pri-orit ies.

Compiking Joumsf Data

The ./CR’”analyzes and summarizes a massiveamount of data: the 1975 listings are based on5,395310 citations from the references of approximately 420,000 source items published in1975 issues of some 2500 SCl source purnals.

Obviously, it will be easier to use informationfrom the .lCR if one understands how it has beencompiled. The user must remember that the JCRis a calendar-year report, cwmpiled from theScience Citation Inde.-& (SCP ) data base.

The SC1 indicates the reference/citation ]inksbetween an article published during the year andall previously published articles cited in the cur-rent article’s references. The SC/ identifies everyunique link between any cited article and all arti-cles that have cited it during the year, supplyingauthors’ names, journal titles, journal volumeand page numbers. and year of publication. TheJCR extracts from each of these unique citationlinks four pieces of information: two journal titlesand two publication years. One of the extractedjournal titles is that in which the current citingarticle was published. The other journal title isthat in which the cited article was published. Oneof the publication years is that in which the cur-rent citing article was published. Since the JCRis a calendar-year compilation, this year date willbe the same in all cases. The other publicationyear will be the year in which the cited articlewas published.

In this extraction process many similar linksare generated from the millions of different andunique links identified fully in the SC1. The JCRcounts how many of these similar links there noware, and tabulates the results in its two ‘detail’listings, first by citing journal and then by citedjournal.

Article-to-Articfe Links

h is important to remember the way thesecounts have been generated, as described above.They are counts of referencdcitation links, notcounts of articles, nor of journals per se. For ex-ample, a 1975 article published in Journal of the

American Chemical Society may have had 40 re-ferences. These 40 references contained, let us

say, citations of only 35 dlflerent articles. The 35different cited articles appeared in 10 differentjournals. In other words, the 40 references citedsome articles--at the most S--more than Onm,and cited each of the ten different journals anaverage of 4 times. In compiling the JCR. it isthe number of different article-to-article linksthat is counted. In this case the Journal of rheAmerican Chemical Society k credited with 35unique references. Their 35 citations will be dis-tributed among the 10 different cited journals,each receiving on the average a ‘cited’ count of3.5--not 4. and not 1.

Lest this point be passed over as a laboring ofthe obvious, the user must remain aware that theJCR represents only one of several possible de-scriptions of journal relationships. Others havebeen suggested above, namely, one based ondata incfuding duplicate citation links betweenthe same two articles, and another based on dataincluding only unique joumaf links rather thanunique article links between the same two arti-cles.

The Ever-Changing Riverof Journals

Many users will need no reminder that the

management of serials, among which are in.eluded scientific journals, is one of the thorniestthickets of bibliography and librarianship. Evenknowledgeable estimates of the number of extantscientific and technical periodicals vary sowidely--by tens of thousands--that the uninitiatedcannot be blamed for doubting the competence ofthose concerned with the problem.

Like a real river, the river of scientific andtechnical publication is ever-changing. Its ele-ments are complex, its cuurse confusing, butwerall the difficulties and problems of serialshbrarianship in science are a reflection of thestrength and force of its river’s progress. Jour-nals die but are replaced by others: journalsBrow,and split into sections (letteredor num-beredor subtitledand resubtitled),or into newioumals;journalsmay narrowtheir interestandmerge with other journals under old or newtitles; titles change to reflect a reorientation evenwhen splitting and merging is avoided--a fewwords are added, some dropped, the language ofthe title itself may change.

This characteristic but vital inconstancy of sci-entific publication is severely problematic for aneffort like the JC#’that seeks to describe journalrelationships over periods of time. There is, to besure, the additional confusion contributed by in-correct or ambiguous citations, by the sometimestruly stultifying virtuosity of title abbreviators,by the ‘separateness’ of original and translatedversions of the same journal, etc. As irritatingand time-wasting as such things are, they are

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nevertheless of relatively minor significancewithin the total complex framework. Most areamenable to easy solution, given persistence,generous computer time, and the ability to sur-vive seemingly endless deserts of boredom. (Onevery soon ceases to wonder at the reason behindsome probably reasonable researcher’s decisionto abbreviate in yet another way the title of theComptes Rendus of the French Academy of Sci-ences. )

When and When Not to CombineCitation Counts

The user is advised in any detailed chronologi-cal study to make use of the cross-references inthe annually issued SCfiuide and Journal Lists,and to consult periodical directories that providehistorical and genealogical information aboutserials, such as Ulrich’s or CASSI.

Compilation of the JCR has, as thoroughly aspossible, dealt with these ‘minor’ problems. Ma-jor problems of identification remain, however,and the user and researcher must not expect thatthey have been ,solved. Any general attempt todo so would have been misguided and inevitablyabortive. We have, thus, in compiling the JCRrefrained from combining journal counts on thebasis of ‘lineage’, even when it is clearly de-finable. Except where a title change has been sominor (usually among latter words) that it neither

affects the title’s position in a catalog listing norrequires additional or different entries, the JCR

does not combkre counts for related journals (re-placements, superaedents, continuations,descendants, etc. ). Nor does it combine countsfor ‘sections’ of ‘the same journal’. JCR leaves itto the user to decide whether or not his purposerecommends that counts be combined in suchcases.

A particularly well-known example of thisproblem is that of Soviet journals and their trarts-Iations. To alert the user, an asterisk after amain entry or subentry abbreviation signals thatthe journal appears in the JCR with counts forboth original and translated versions. Unfortun-ately it would be impractical to attempt anythingsimilar for the hundreds of journals that arelineally or otherwise related to others in theselists. When, for special purposes, counts havebeen combined, the user is informed.

ChmtOst!

Caution ia advisable in comparing journals, es-pecially journals from different disciplines. Thejournal literature varies in its importance as ameans of disseminating information in differentfields. Wide citation may be necessary practice

n one field, but because of other disseminationn others a redundancy. Citation practices differ‘rorrrone field to another, The d~fference may beimplicated by a difference in the half-life ofournal literature in different fields, as well ashe size of the extant citable literature. Rapidobsolescence may characterize one field but notmother. Thus, for example, it would be foolish to:onclude merely on the basis of citation countshat Journal of the A mericrrn Chemical Society is~ ‘better” journal than Annals of Mathematics, oro hypothesize, without a great deal of study,~,hich serves its own field ‘better’.

Other factors must be considered as well. For:xample, journals that do not use the remanalphabet are not as easily and economically in-:Iuded in the SC] data base as those that do. Thisfact may affect the ranking and citation counts ofsome Russian and Japanese journals, Or a journalmay have published two or three articles that arecited year after year with extraordinary fre-quency, compared with the ‘average’ article ithas published. Citations of such papers may dis-tort evaluation of the journal unless their recordsare taken into account.

II. Why the

Jowwd Citation Reports?”In other parts of this introduction 1 have tried

to explain the source of tbe data in the JCRT todescribe how the material has been summarizedand dk.played in its various sections, and to helpthe novice use it for the first time. The JCR an-swers the following types of questions immedi-ately: how often has a particular journal beencited? what journals have cited it? how frequent-ly have portictdar journals cited it? is it the olderor new material that’s being cited? what journalsdoes this journal cite? how often does it cite eachof them, etc. ?

A merely curious browser, or even students orresearchers, may reasonably and bluntly ask why

these questions should be asked. What is thevalue of answering these questions? Can itjustify a work of the JCR’S scope and expense?What is the mtionafe of such questions, beyondan academic itch to know? Who wants or needsthe answers? Why is it necessary to comparejournals or to determine their importance?Ooesn’t the mere fact that a journal is publishedsay--with inarguable economic authority--allthere is to be said? Aren’t journals publishedbecause they are important to someone or tosome group? Unfortunately iife isn’t that simple.

This introduction is no piace to go into thecomplicated economics and politics of scientificand technical journal publication. The subject de-serves several dnctoral theses. In due course, the

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JCR will undoubtedly stimulate students to un-dertake them. Suffice it to say the ‘authoritative’voice of economics can speak in barely more thana whisper. Indeed it can often hardly be heardfrom its shaky podkm, of subsidized and un-subsidized society sponsorship, tint- and back-dmr government support, voluntary and manda-tory and “man&tory-voluntary’ page-charge sys-tems, advertising and public relations programs,etc. The sheer economic chaos of much of thisimportant activity is alone good enough reason toattempt to answer questions like those posedabove.

For that very reason, the JCR should quicklyprove itself indspenasble to people who cannotrely on economic criteria alone in making basicdecisions about journals, since the law of supplyand demand is not always allowed to prevail.Tlreae include administrators in libraries and in-formation service centers individual scientists;journal editors and publishers; and those whodetermine science policy and measure its accom-plishments.

Librarians can use the XX to counteract theinertia that too often prevails with regard topumal selection. [t’s just too difficult; therefore,ad hoc decisions are rampant. llre JCR offera ob-jective evidence of the optimum makeup of gen-eral and special journal collections. Its yearlyeditions will indicate or imply changes the libraryshould consider. The chronological spread of ci-tation counts should be invstuable in optimizingretention schedules. Why keep twenty-five yearsof a journal on your shelves when 80 to 90% ofits cited material is less than six years old? Fewtibraries in the world have a mandate to collecteverything and none can afford it. Most mustoperate within a budget on which users’ journalrequests can wreak havoc. Because the JCRgives gocd indication of a journal’s overall use, itprovides a starting point for tme cost-benefit an-alysis in allocating acquisition funds.

Outside the library or information center’s ad-ministration offices, the JCR can be as useful tothe librarian as to the library user. At H#wehave found the JCR to be the most reliable--sometimes the only reliable--indicator of a jour-nal’s subject area, and of its orientation withhthe subject area. One quick scan of the mhsmnsshowing journals that it cites and that cite it canoften be more informative than the best title orstatement of a journal’s editorial objectives. Thiscapabltity of the JCR is especially uscfid as mul-tidisciplinary work takes scientists to the bordersof their own fields, and perhaps over them intoothers with less familiar journals and journals nfd~fferent types. These same cited and citing listsreveal what journals in other fields are linking upwith journals in their own. And, a far from trivialmatter, the JCR can be very helpful in deciding

where to publisb to reach the audience you wantto reach. If, for example, you have ● paper that&als with some interesting mathematicalaspects of biological problems but is neverthelessdefinitely a biological paper, the JC#’can showyou which biological journals have the best ‘con-nections’ with math, and whklr are most fiiely towelmme the paper.

Since publication of the preliminary 1%9 cdl-tion of the JCR we have had many inquiries fmmjournal publishers and editors. Those inquiriesseem to me to speak not only for the potential ofthe JCR but also for the managerial acumen ofthe scientists and business people who expressedimmediate interest in JCR. As made plainearlier, the JCR cannot be used alone in evsdua-ting a journal’s performance, but it can alonegive reliable indication that a thorough evahsa-tinn--including use of the JCR--may be in order.Has the number of citations dropped in relationto number of articles published? Has the rate ofself-citation remained steady at the expectedaverage? How do the self-citing and self-citedrates compare? How are citations distributedsmong citing journals within and outside the spe-cialty? What is the impact of the average citedarticle in comparison with other comparably citedjournals? How rapidly -- see immediacy hsdsx

Imong the De@ritions--is the journal’s material~oted in the references of other pumals?

The use of the JCR can be of far-ranging sig-nificance in a field abnut which I can say leasthere--science--its planning, its evsfuation, its so-ciology, its history. Citation analysis can be usedto identify and map research frontx to definedisciplines and emerging specialties throughjournal relationship to determine the interdki-plinary or multidisciplinary character and impactof research programs and pmjeets. I say leastabout this, to me the moat exciting aspect of itspotential, because the JCR in its present form is,for such advanced applications, only a sketch ofthat potential, providing tiile more than sugges-tions for further and deeper examination of themassive data bank from which its sections havebeen estracted. I have made plain above my re-gret that this book has dimensional limits. Evenfor the generally straightforward lists of rankedand citing and cited journals, we have had tolimit the data presented. For the study of scienmpolicy and smiology those timitations are moretroublesome to me. I believe the JCR in itspresent form can certainly providematerialforinnovativeresearchin the field. But it will servethe field best if it does, as 1 hope, promptmoreimaginativeanalyses than 1 am mmpetent toattempt.1 shallbe verydisappointedif theJCRdoes not, as any good piece of scientific workshould, stimulate with every answer it givesmore questions that need answera.

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III. Definitions

TheseDefirsirions are, in some cases, actually defnritiorrs. fn others, they explain U.SSWSpedier tothe .fCfland the JC~and their editoriaI conventions. In stifl others (e.g., cited jossmd. chbrg jourrdtimes cited), the delhtidrrn is meant primarily to warn the reader that, in the case of the JCR, them ismore than initially meets the eye in these apparently obvious terms, and tiequently mom than thememory instantly discloses. The user will need a fair command of their meaning when reading thedescriptions of the Citing and Cited Josmsal Packages.

CttaItlorr. When one document (B) mentions, or have an advantage, as regards immediacy, overrefers to another dwasment (A), the latter (A) has journals published quarterly and semi-annually.been cited by the former (B) as a source of itr-formatiorr. as suppnrt for a Pint Of view. as au- lmp~t F=tQr. A measure of the frequencythority for a statement of fact, etc. The word ci- with which the ‘average cited article” in a journaltation is used to indicate not only the fact that hdocument A has been cited in a reference of

as been cited in a particular year. The JCR

document B. but also for the description of docu -impact factor is basically a ratio between cita.tions and citable items published. Thus. the 1979

ment A contained in the reference (Ls4erbqf J. jrnpact factor of journal X would be calculated byJ, Buct. 63:399. 1952). hr this sense. Citation and di~iding the number Of all the .$cf sOur~ jour.reference are frequently used interchangeably. nals’ 1979 citations of articles journal X pub-

lished in 1977 and 1978 by the /oti?/ number ofatskfosl Idex. The Cira~ion index is an alpha- sourcc items it published in 1977 and 1978.hetic list. by first author. of items cited in refer- TI.w.re arc other ways of calculating journal im-cnces from footnotes or bibliographies Of a pact (see G~efrf E. Citation analysis as a tmI insource article, Each such citation is followed by a journa] evaluation, science 178:471-79. 1972; es-shorr bibliographic description of the source al’ti- pcially note 27),CICwhich contained the citing reference. The impact factor is useful in evaluating the

significance of absolute citation frequencies. It

Cited Jmrrruxf. A journal cited in a reference of tends to discount the advantage of large journalsan itcm (source item) published in an SCI source over small ones, of frequently issued journals

journal (citing journal). A cited journal is not over less frequently issued ones (weeklies vs.necessarily covcrcd by the SC/; that is, it may quarterlies or annualsk of older journals overnot bc found in the listing of citing .iournuls. newer journals. [n each such case the first isMxt cited journals. however. are also citing Iikcly to produce or have produced a larger cit-

journals. Cited.ioumul is used as a column head - able corpus than the =cond. All things beinging in the Cited Jourrrul Puckage of the JCR equal. the larger that corpus. the more often altcms in that column may include so-called ‘s@ ‘ pumal will be cited. The impact factor allowsjournals, and other serial publications. SUCh some qualification of quantitative data. Thectrtrics have been retained for their informationn qualification is algorithmic and objective, butvalue. nonetheless useful in pumal evaluation.

Cithsg Journal. A jrrurnalin which publishedi!cms contairrcd rcfcrcnccs citing another journalor published itcm. In the JCR, citing journals arenecessarily source.icummds of the SC!.

kssmedkcy Index. A measure of how quicklythe ‘average cited article’ in a particular journalis cited. A journal’s immediacy index considerscitations made during the year in which the citeditems were published. Thus, the 1979 immediacyindex of Journal X would be calculated by divid-ing the number of all journals’ 1979 citations ofitems it published in 1979 by the tots/ rrumber ofsource items it published in 1979. h should beobvious that an article published early in the yearhas a better chance of being cited than onepublished later in the year. As a result. journalspublished weekly and monthly will theoretically

Jsmmaf TMe. The title of a scientific or techni-cal perio&cal. usually givers in the .fCY/’fn an ab-breviated form. Abbreviation of titles in the ./CRusually ignores subtitles and title run-ons (Actsmedics clinics--an international jnuma[ of medi-CUI practice. Zeitschrift fiir Neurologische For-schung srrrd Arrgeswmdte Gebiete). In abbrevia-tion of journal titles, consistency is subordhsatedto informativeness and clarity, as far as spaceallows. In alphabetic listing of journals, abbrevia-tions are alphabetized letter by letter, with aspace regarded as a ‘letter” preceding A and ahyphen as a “letter” following Z. In such alpha-betic listings of ‘journal titles’ in the JCR. notethat it is the abbreviation. not the full journaltitle, that is alphabetized. An Abbreviated-to-FulfTit/es ofCiting/CitedJossmals list begins on page40.

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Reference. The mention or description of omdocument (A) in another dcvaiment (B), to indi.catc a source of information, to provide supponfor a point of view. to lend authority to sumcstatement of fact. ctc, Document B is said tcmake rcferencc to dncument A: document A issaid tn be cited by document B. Re/iwwrce is alwused for the document description or bibliographic data given in making tbc referenct

(Lederberg J. J. EUCI. 63:399. 1952). Referenceis made. that is. references arc given. in footnotes. and more frequently among bibliographiccnd.notes or in bibliographic listings at [hc cncof an art iclc. Frnm such rcfcrenccs are cd ractccthe ci[ufions which bccomc mairwcntrics in thtCitution lttdex.

Rest. A column heading in the Citing and Ci#ed

Jourmd Packages uf the JCR. used to mean‘Tntal Citations of Amicles Published in All Pre-vinus Years”. Since the format of the JCR allowsa chronological distribution of citation dates overu Icn-year period. Resf means ‘published prior tothe dccadc just ended”.

Seff-Cftatkoxs. Self-citation of journals ocersrswhen an article in journal X cites another articlepreviously or simultaneously published in journalX. Self-citations are contained in about 207. of ajournal’s references.

Seff.Cftatfms Rate. Self-citations expressed as apercentage of all citations. There are two aelf-citation rates, the self-citing and self-cited rates.The self-citing rate relates a journal’s self-citation to its total references. The self-cited raterelates a joumal”s self-citations to the number oftimes it is cited by all journals includhsg itselfFor example journal X made reference to 1000Citems, including 2000 items it itself had pubIished. Its self-citing rate is 2/10 or 20?70.On theother hand, journal X was cited 15QO0times irthc references of all journals, including its ownIts self-cited rate is 2/15 or 13.37..

Source Index. The Source Index of the SC;gives a complete bibliographic description of al’source items processed for the SC/. Items artarranged alpbabctically by name of first authorall coauthors are cross-referenced to first authors. The Source /srdex is. thus. an alphabcti{index by author of all items published by SC/twvcred journals during a particular year. or during the time covcrcd by any of the cumulation oSC/ annuals.

Source Item. Called also source documentsnurcc article. a source item is an itcm publishe{in one of the source journals processed for th~

icience Citufion /rrdex-(SCfl. Source items may)C original substantive articles. editorials. let-crs, technical notes. correction notes. meeting,cports. reviews, etc. From thc references pro-Iided by a source item, citations are extracted towcparc the Cifu/ion Index of the SC/; biblio-graphic descriptions of source items are preparediw the Sourer /ndex of the SC/; and words fromhe titles of source items are paired for pmduc-iorr of the Permsdermm Subject Index of theFcl.

Snmc types of source items (e.g.. news items.mm-scientific and non-technical corrcspontlence)10not by their very nature invite citation in theeferences of scientific reports. Such source!ems are excluded from source-item counts inompilation of the JCRrn In the JCR only originalrficles, technical notes and review articles areourrted as source items, except in the case of theallowing journals, whose meeting abstracts aredmitted as source items in impact-factor andmmediacy-index calculation: Federation Pro-ceedings. Bsdletin of the A men”can Physical So-

iery. Clinical Research, Transactions of theImen”can Nuclear Society. and Nasices of theImerkarsMathematical .%ie~.

iaree Joomaf. A journal that is processed forhe SCI,” so called because it is the source oftublished items processedfor compilationof thehree sectionsof the SC/. In the JCR a sourcemtmal is a cifing journal.

~mes CttesL The JCR describes relationships)etween journals. It is, however, based on cita-ion links between articles. The following ex-Aanations of “times cited” may be unnecessaryor most users. Some, however, may need thenformation, and it is given in some detail in thentcrcst of whatever differentiation research may.cquirc.

f’fmeaCltsxk Autksara. in the case of authors,‘times cited’ is the sum of the citation of theircited items, as descrikd below. inclu~lngjournal articles. beoks. etc.

Tlmea C2teshJosrrssak In the case of Purrrals.3times cited” is based on citations of articles, asdescribed below. It is a cumulation of the num-ber of times a particular jouraal has been namedin citation of different articles in references ofindividual source items.

Tfrnea Cfkf: Adcfea. As elsewhere in thesedefinitkmts, the term arric/es is used broadly for‘pumal items’. and includes technical communi-cations. letters to the edkor. editorials, etc.; inrrthcr words. individual items published in jour-nals. An articfe cited three times in the refer+

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. . . . . .ences of the same SCI source item is counted ashaving been cited by that source item once.Thus, ‘times cited’ in the case of articles is thecumulative number of times the article has beencited once or more by single SC1 source items. Inthe case of articles, therefore, ‘times cited’ isequivalent to the number of source items thathave cited the article.

Tkrtsea Cited: Books and CJtJser *Non-JmarrsaYItems. The references of journal items containcitations of many different types of publications.About 80?J0 of the references cite other journalitems. The remaining 2070 cite books (single- 01multi-authored monographs); edited collectionsof single- or multi-authored ‘contributions’ ot“chapters’ or ‘sections’; variously compiled andformatted collations of reports and papers produced by meetings, symposia, congresses: technical reports of academic, industrial, and governmental origin: personal communications; items ilpress: theses; ‘unpublished’ reports collectetworks of classical and modem authors; handbooks. textbooks, data compilations, encyclopedias and other reference works; etc.

A great deal of such material presents prob

Iems tar cttatlon analysls that the Journal arhcledoes nol. First, styles of citation vary widely andwildly. Second, internal citation (of a singlepage. series of pages, section. chapter. etc. ) isparticularly frequent. Third. different revisionsor editions. by the same author(s) or by the sameor different editor(s), may bc cited.

Such items cited more than once in the re-ferences of the same SC/ source item are takenas cited as many times as there are differentforms of citation. Thus. if John Smith’s ClassicCJremis/ry is cited three times identically as“’Smith J. C/assic Cherrristty. New York: ABCPubI,. 1954, ” it is counted as having been cited

once by the citing article. If, however, the threereferences cwntain citations such as (1) “Smith J.Clussic Chemistry. 1ss esf., New York: ABCPubI.. 1954, p. M:”’ (2) Smith J. Classic Chem-istry, let cd., New York: ABC PubI., 19S4, p.Eid;”and (3) “Smith J. Classic C/fernisrry. 2rsdrev. esf., New York: ABC PubI.. W&t,” Smith’s‘book’ (and Smith) will be taken as having beencited three times. Thus, ‘times cited’ in the caseof such ‘non-journal’ items is the cumulative sumnf their single or multiple citation by individualSCI source items.

IV. Components of the jCR”

The JCA is made up of three data ‘packages’ or sectbns. We have retakd the word “pack.sgea’ in thetitles of the sections tivm their first pubtkkation in the form of computer printouts. The three sections are:(1) Journal Ranking Package: (2) Cskirrg Jasimal Package; (3) Cited JasrmaJ As&age.

The first section (Jarsnssd Ranking Package) lists cited journals alph&eticsdly and then ranks them byfive different counts or indicators.

The second section (Citing Journal Package) shows for each SC[ ● source journaJ the journals it cited in1975, ●nd the chronologkcaf spread of items cited.

The third section (Cited Joawrsal Pockage) shows for each purnsf cited by SCl journals, the SC] sourcepumals that cited it, and the chronological spread of items cited.

Each of these sections is described more fully in the material whkh follows.

IThe Journal Ranking Package

The first part of the JCR is the Journal Rank-

ing Package. It contains six listings, described indetail on pages 10-13. The first listingis an al-phabetic list of journals cited in the 1975 re-ferences of journals prcxessed for the productionof the Science Citafion hsdex” The remaining Jivelistings rank the cited journals by various muntsand indicators.

The ranking lists present a great deal of usefulinformation. Some of it is a summing of counts of

references made and citations received that arebroken down by cited journal and by citing jotsr-nal in the two larger parts of the JCR. Sense of

the information is presented only in these lists;for example, the number of source items pub-lished in the years 1973, 1974, and 1973 by eachof the cited journals. It can be somewhat dlffkultinitially to understand the calculation of impactfactor and immediacy index, as defined in tbeDefinitions elsewhere in this introduction. Thesumming of counts presented in tbe JoumrdRanking Package gives the counts involved in thecalculation of botb, along with the result. Impactfactor is the result of dividing the cwtnt in thefourth column of figures by the count in theseventh column. Immediacy index is the result of

dtviditrg the count in the next-to-last numericalcolumn by the number on its left.

564

The fact that there are five ranking lists will, Ihope, serve to remind users that ranking journalsby any single criterion can be highly useful. Butthe result must be usedwithcaution,and not inisolation without consideration of other rankingsand other factors which may not be susceptible toany kind of ranking or any khd of objective,especially algorithmic comparison. Not un-

necessarily, this advice of due caution is re-peated elsewhere in this introduction. and inmuch else that the author has written on the sub.ject, The user must remember that rank in theJCR indicates relative standing on certain lists,and that the JCR is, among other things, a fordfor evaluation of journals, not itself an evaluationof ioumals.

Journal Ranking Package, Section 1:

Specimen

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Description

Section I is a listing of journals cited in 1974 inthe references of SCl*&mrce journals. The jour-nals are arranged in alphabetic order of title ab-breviation (letter by letter, with space precedhgA and hyphen following Z). The first column isan item number. The semrnd column is the jour-nal-title abbreviation. The next four columns,bracketed under the heading ‘—Citations in1974 to---’ give:

(1) the total number of times the journal wascited by individual Ss21 source itemsin 1974;

(2) the portion of those total citationsaccounted for by articles the journal pub.Iished in 1973;

(3) the portion of the total citations accountedfor by articles the journal published in1972; and

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(4) the sum of 1972 and 1973 items citedin 1974.

The nest three columns, bracketed under theleading ‘—source Items in—‘, give

(1) the number of source items published bythe journal in 1973;

(2) in 1972; and

(3) in those two years together.

le nest column, headed ‘Impact Factor’ gives aigure for the relative frequency with which themmal’s ‘average cited article’ has been cited.See Impact Factor under Definitions above.)Iriefly, the impact factor ia the ratio of citationso citable items published: all journals’ 1974 cita-ions of 1972 and 1973 items published by journal[, divided by the total number of source itemswblished in 1972 and 1973 by journal X.

‘fire next two columns show, respectively, thelumber of times articles in the journal’s 1974

565

issues were cited in the references of 1974 SCf4source items; and the number of source items thejournal itself published in 1974. The last column,headed ‘Immediacy Index’ (see that term underDejirsitions above) is the quotient of 1974 cita-tions divided by 1974 source items.

Thus, we see that Acts A rsaesthetica Scan-dirmvica was cited by all SC{ snurce journals 287times in 1974. Of those 287 citations, 62 were ci-tations of articles published in 1972 and 1973issues of Acts A rraesth. Scancf. In 1973 thatjournal had published S4 source items; in 1972, itpublished 48. These 102 items (54 -t 48), pub-lished by Acts Arraesfh. ScarId in 1972 and 1973,were cited in pari by SCf source journals 62times in 1974. as we have seen. The impact fat.tor is therefore 62/102, or 0.608. In 1974, AcmAnaes:h. Stand. published 61 articles. to a few ofwhich there were, dun”ng /974; 8 references. Theimmediacy index is thus 8/61 or 0,131,

In some cases, a column will show a zero, asmall bullet. or a blank. A zero is always a truezero; a small bullet indicates lack of data; a blankindicates an incalculable figure,

It should be remembered, as noted elsewhere.that the journals variously arranged in the sec-tions of the Journal Ranking Package include not

only SC) source journals themselves, but alsoother journals they have cited. In most cases, wehave been able to supply the information onitems published in the perind 1972-1974 that isneeded to fill out the entry for each cited journalnot covered by the SC1. Where we have not, asmall bullet appears.

There will, naturally, always be actual countsin the first column of these listings. A zero in thesecond to fourth columns of the ‘—Ci.

tations in 1974 to----’ group is a true zero.Abrasive Engineering, for example, was citedonly once in 1974; that citation was of an articlepublished in some year other than 1972 or 1973,and the three columns for those two years’ ci-tations and their sum show zeros. Both impaclfactor and immediacy indexes are therefore alsozero.

Zeros in the second group of columns headed‘——Source Items In—’ usually indicatethat the journal is no longer published or nolonger published under that title. A small bulletindicates the few cases in which we have beenunable to determine the number of source items.For example, AcIa CrysfaHographica was cited7598 times in 1974. Of those citations, 40 weresupposedly citatioir% of articles published by‘Acts Crystallographic” in 1972 and 1973. As thereader may know, however, the former Acra Cry-srallographica had by 1972 split into separate Aand B sections. Cnunts for those new journalsimmediately follow the entry forthe formertitle.As shown, ‘Acts Crystallographic’ publishednothing in 1972 and 1973, or in 1974, but in-complete citations in 1974 references of somejournals failed to identify which of the A or Bsections was meant. The original title is stillhtghly cited, but cannot be given either impactfactor or immediacy index. Both appear for the Aand B sections in the entries below. The journalorigin of the 40 incomplete citations can be par-tially determined by consulting the Cited Jour-

nal Package.

As an alert for the user, an asterisk follows theabbreviation of journals (usually Russian) which

appear in the listings in both original and trans.Iated versions.

Journal Ranking Package, Sections 2-6:

Specimen

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566

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DescriptionIn Section I of the Journal RSrtrkirrgPackage,

cited journals are listed alphabetically by journaltitle abbreviation. In Sections 2-6, cited journalsare rearranged in descending numerical order ofcounts or indicators in various columns, as fol-lows:

Section 2. By total citations for all yearsSection 3. By impact factorSection 4. By immediacy indexSection 5. By source items published in 1974Section 6. By number of 1972 and 1973 cita-

tions in the references of 1974issues of SC/%ource journals.

in Sections 2-6, the first column is a ‘rank’number. In these sections. journals will have thesame rank number when they show the samenumber or value for the cnunt or indicator thathas determined the ordering of the entries. Afte!one or more repetitions of a rank number, thenext lower rank number is advanced as man)times as necessary to compensate for the repetition(s). Thus. in Section 5. B CHEM SOCJAPAN, J APPL CHEM-USSR* , and ZH PRIK1KHIM* all rank 37th in terms of source item!pubtished in 1974. The next journal on the list. JGEOPHYS RES. ranks 40th.

Once familiar with the JCR*and its potential irjournal evaluation. readers will find they want informat ion about part icular journals from seversor all of the lists in Sections 2-6 of the Joumu

BankingPackage. To find the rank of a particularPumal on any of the lists, Inok it up in the alpha-betic list. Determine the count or indicator in themlumn by which you want the journal ranked,turn to the indicated Section of the Jaumaf Rarrk-brg Package, and run down the relevant columnuntil you find the journal’s count or ind~atorDne can of course work from any one of theSections to any other in this manner, withoutbeginning with the alphabetic listing in Section 1.

For example. in the alphabetic list of Section 1.Science is number 232S on page 20. From thatlist, we find that it was cited 47,S0S times in1974. Turning to Section 2, we do not have to gofar down the first numerical column to find47.S05: Science ranks 7th. Scanning across therow to the impact-factor column, we find a valuenf 5.412. Turning to Section 3. we scan barelyhalf a page to find 5.412 and Science. with animpact factor rank of 48th. Jumping across to theimmediacy-index column. we find a value of1.314, Turning to Section 4, we find Scienceranks 22nd in immediacy. It published 919 sourceitems in 1974: turning to Section 5. we find itranked 27th (the same as FIZ TVERD TELA andSOV PHYS SOLID ST* ) in this respect. In Sec-Iion 5, in the fourth numerical column. we findScience articles published in 1972and 1973 wereci[cd 11.781 times in 1974,Turning (O Section 6,and starting down the fourth numerical column,wc find Science ranking fifth.

567

The Citing and CitedJournal Packages

The Citing and Cited Journal Packages showcitation-frequency relationships between pairs ofjournals. in the Citing Journal Package, one canfind what journals a particular journal has cited,and a distribution by year of the publicationdates of the cited material. In the Cited JournalPackage one can find what journals have cited aparticular journal, and a distribution by year ofthe publications dates of the cited material. Spe-cimens with description from both appear onpages 16-19.

Relatively few journals produce most of thereferences processed for the Science Citation In-dex data base. Similarly, relatively few journalsaccount for most of the citations made in thosereferences. In either case, a list of 1000 journalswill encompass well over 70$’oof the items. Be-yond lists of 1000 journals, the ‘return’ in re-ferences and citations becomes progressivelysmaller as the lists are estended, but that returncan be valuable for the information it gives about‘narrow’ but important specialties and sub-specialties in whtch journals may he few, publi-cation infrequent, research relatively slow-paced,and so on.

Ratios like the XR’S impact factor and im-mediacy index do much to compensate for sheersize in ‘comparing’ one journal in biochemistrywith another, for example, or in ‘comparing’ abiochemistry journal to a paleontology journal.But even with the help of such indices, we mustextend the lists of citing and cited journals wellbeyond the select but gigantic core if we are todo justice to as many of the ‘narrower’ fields andsubspccialties and border-marches of science aspossible.

The Citing Journal Package includes entriesfor each of the 2540 journals covered by the SC/in 1975, provided that issues of the journal did

appear during the year, or, as in the case ofsome ‘annuals’, appeared with 1975 cover datesduring the early part of 1976. The Cited JourrsufPackage includes entries for more than 250ttjournals and other items, some of them obviouslynot covered by the SCf. As noted above, journalreferences contain citations of other items be-sides journal articles. As far as possible, citationsof non-journal material have been deleted in

compiling the JCR. Ched subentry items- in theCiting Journal Package and main entries in theCited Journal Package will, therefore, be journa/s in almost all cases. Since exclusion ofnon-journa} material from these listings has beenalgorithmic, a non-journal item may appear oc-casionally as a cited-journal main entry, or as aciting-journal subentry.

It would have been uneconomical to give forevery citing journal all the journals it cited, andfor every cited journal all the journals that citedit, To do so would have made thk volume manytimes its actual size, but would have added to itin either case mainly long strings of singly citedor citing items under every main entry. To avoidtbe latter, but at the same time to avoid neglectof journal relationships in ‘smaller’ and ‘nar-rower’ fields, the length of subentry lists hasbeen controlled in both the Citing Joumaf Pack-age and Cited JournalPackage.

The following algorithm was adopted to controlthe length of subentry lists. Subentry lists ofcited or citing journals are limited to a maximumof 100 items, or to the number of items thataccount for 75% of the total references or ci-tations. Where either condition would allow list-ing of items cited or citing less than 6 times inthe year, the items are not printed as subentriesbut are incorporated in the ALL OTHER sub-entry, the last subentry under each main entry.Disregarding these conditions, at least six sub-entries in addition to the ALL OTHER subentrymust be printed, if the main entry journal cansupply them.

Complete citing and cited data on all the listedjournals are available on magnetic tape for userswhose research requires it. inquiries should bedirected to the Research and Corporate Development Division, Institute for Scientific hrforma-tion, 325 Chestnut Street. Philadelphia, Pa.19106, USA.

Main entries in the Citing Journal and Cited

Journal Packages are arranged alphabetically byjournal title abbreviation. As mentioned else-where, consistency in abbreviation of journal titlewords has been subordinated to informativeness,The same word may not be abbreviated in thesame way whenever it occurs. The reader can‘decode’ any abbreviations that may leave him indoubt by referring to the Abbreviated-to-FullTiiles Of Citing/Cited Journals list beginning onpage 40.

568

Citing Journal Package

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duced 1090 references with unique citatiOns (ci-tations of the same article in a single article’sreferences are counted as one). Twenty-six of the1090 references contained citations of articlespublished in 1974, 92 references cited articlespublished in 1973, 115 references cited articlespublished in 1972, etc. The last column in thecow shows that 432 of the 1090 references con-tained citations of material published in 1964 andearlier years.

Under the total line for each citing journal arelisted the journals cited in the references of theciting journal named in the main-entry line.These cited journals are listed, in descendingnumerical order, by the frequency of their cita-tirm in references of the citing journal named inthe main -entsy total line. The abbreviated title of

DescriptionCiting journals are listed in alphabetical order

of their abbreviated title. ‘llrus, in the specimenshown, the entry for Mathematische Zeitschrt~(MATH Z) comes before the entry for Mathema-tika (MATHEMATIKA). The first line of theentry for each citing journal gives its impact fac-tor, abbreviated title (in most cases), and totalnumber of unique references from articles thejournal pubfished in 1974. The total is asterisked.Succeeding columns of the row distribute the re-ference total by year in which the articles cited inthe references were published. The last columnincludes counts for 1%4 and previous years.

Thus, the specimen shows that articles pub-lished by Mathematische Zeitschrrfi in 1974 pro-

569

cd.11 w urc suo-enwy Clrea JmSmalS 1s precededby the impact factor of that journal if it has beenpossible to determine it. The total citation countfor each sub-entry cited journal is shown, andthen distributed, as described above, by year 01publication of the cited items.

Thus. Mafherrwfische Zeifschrift cited itself151 times in the references of articles it pub-lished in 1974. Of those 151 citations, 5 were ofarticles published in 1974, 24 of articles pub-lished in 1973, 18 of articles published in 1972,etc. Thirty-six of the 15I citations were of articlespublished in 1964 and earlier yeara. Similarly,Mathematische Zeinchrifl cited MathernatischeAnna/en (MArH ANN) 60 times in the refer-ences of articles it published in 1974. Four ofthese references contained citations of articlespublished by Mathematische Annolen in 1974,icuntained citations of articfes published byMathematische Anrralerrin 1973.and w on. Thechronological distribution shows that more thamhalf (34/60) of Mathenraiische Zeitschrrfi’s cita.t’mnof Mathematische Anna\en was of matetialpublished by AfathetnatischeAnnalen in 1964and earlier years.

-.. . . . . . .IIre last suo-emry unaer each cnmg puma!

main-entry summarises data on pumals thatwere cited less than 6 times in the references ofarticles published in 1974 by the pumal namedin the main-entry line. (Exceptions to the ‘less-tharr-six’ convention are explained elsewhere).Thus ‘all other’ journals cited in 1974 referencesof Mathematische Zeitschri~tnumbered 217, andthese unnamed cited journals accounted for 354articles. The total for ‘all other” journals is dis-tributed chronological y. as described above fornamed cited journals.

This specimen shows that about 40?4 (432/IC190)of the articles cited in 1974 references ofMarhematische ZeitschnJi were published in1964 and earlier years, that its self-citing rate is13.8% ( 151/1090). that language seems to be oflittle hindrance in mathematical studies (therearc English, French. Gerrnarr. Russian, Japanesejuurnals on this cited list), that AfarhemafisckeZeirschr@ seems inclined to an interest in phy-sical and applied mathematics. and that 42.670(464/10953) of the articles it cited in 1974 werepublished in 1%9 or thereafter.

Cited Journal Package:

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570

DescriptionCkedjoumats ate lieted in alphabetical order

of their abbreviated title. Thus, in the specimenabove, the entry for American Journal of Physics(AM J PHYS) comes before the entry for Anreri-crm Journal of Physical Anthroplo@ (AM JPHYS ANTHROFOL). The first line of the entryfor each cited joumai gives its impact factor,abbreviated title (in most eases), and total cita-tions received in 1974. The total is asterisked.Succeedng eohsmns of the row distribute the ci-tation total by year in which the cited articleswere published. The last column includes countsfor 1964 and previous years.

Thus, the specimen shows that Amen”can Jossrnol of Physics (AJP) was cited 800 times in 1974by SCf$ource journal items. Fourteen of the ar-ticles or other items cited in 1974 were publishedby AJP in 1974,95 in 1973, 104 in 1972, etc. Ofthe S00 citations, 230 were of articles publishedby AJP in 1964 and early years.

Under the total line for each cited joumst arelisted the journals its whose references citationsof the main-entry cited journal appeared. Tbeaeciting joumafs are fisted, in descimdkrg numeri-ral order, by the number of citations each contri-buted to the citation totals for the cited journalnamed in the main-entry total line. The abbre-viation for each of the sub-entry citing journals ispreceded by the impact factor of that journal, if ithas been possible to determine it. The total cita-tion count for each sub-entry citing journal isshown, and then dktributed, as described above.by year of publication of cited AJP items.

Thus, American Jaumal of Physics (AJP) citeditself 243 times in references of articles it pub-tished in 1974. Seven of those references con.tained citations of articles published by AJP in1974; 60 of the 1974 references cited 1973 AJPasticles,and so on. Similarly, Journal of Chemi-calPhysrks (J CHEM PHYS) cited AJP 29 timesin references of articles it published in 1974.None of those 29 references cited 1974 AJP arti-cles. Of the 29 references from Journalof Chemi-

calPhysics in 1974that cited AJP, 1 cited a 1973AJP article, 4 cited 1972 AJP articles, 2 cited1971 AJP articles, etc. in eight csses, Journal of

Chemical P/rysics cited articles that had beenpublished in AJP in 1964 or earlier years.

The last sub-entry under each cited journalmain-entry summarizes data on journals whose

1974 references included fewer than 6 citations ofAJP in 1974. (Exceptions to the ‘less-than-six’convention are explained elsewhere. ) Thus, ‘allother’ journals whose 1974 references containedcitations of AJP numbered 1S3. These 153 jour-nals contained in all 262 citations of AJP articlesin their references. The total for these ‘all other’journals is distributed chronologically, as de-scribed for named citing journals.

This specimen shows that AJP has a self-citedrate of 30.4% (243/S00); that 28.8% (230/800) of1974 citations of the AJP were citations of oldermaterial published in 1964 and earlier years; that.$cie;ce in 1974 cited AJP as often as Solid StateCommunications cited AJP, and interestinglyenough, that Science cited newer AJP material,while Solid State Communications cited oldermaterial.

The specimen below opposite shows severalfeatures whose significance users will soon un-derstand at a glance. B1OCHEM PHYSIOL VISUwas cited only twice and the cited items are fromthe same year. ‘fire cited work is Biochemistryand Physiology of VisualPigments. a symposiumproduct published in 1973. When all citations, asin this case, are confined to the same year, thecited item is likely to be a ‘soft’ journal, as in thiscase, or as mentioned elsewhere a book of sometype. Where citations arc confined to two orthree years, each separated by a lapse of severalyears. the cited items arc likely to be successivereports from irregularly held symposia, cmsfer-ences, etc., or successive editions of a book.

BIOCHEM SOC TRANS was cited only S02times. The journal is BiochemicalSociety Transac-tions. which began publication in 1973--hence thezeros in most of the right-hand columns. Theseven citations for 1972 items are the result ofincorrect references. The array of zeros on theright alerts the user to the fact that the pumal isrelatively new. As a matter of fact. it replaces aproceedings section formerly included in Bio-chemicalJournal

B1OCHEM Z was cited 2420 times. It shows noimpact factor, and practically no counts for citeditems published atler 1966. In fact 84% (2038/2420) of the citations refer to items publishedbefore 196S. Biochemische Zeirschrrfi ceasedpublication with issue number 5 of volume 346 inJanuary 1%7. It was superseded by EuropeanJournalaf Biochemistry. The ten counts for citeditems published after 1967 are the result of incor-rect references.

571