El Science Citation Index (SCI) va ser proposat fa més
de 50 anys per facilitar la disseminació i recuperació de literatura
científica. El seu cercador era únic pel fet de basar-se en una
recerca per cites, però no va ser àmpliament adoptat fins que
va estar disponible en la xarxa en l'any 1972. El Journal Citation
Reports, que apareix com a conseqüència d'aquest en
1975, incloïa a més una classificació basada en el factor d'impacte.
No era comú utilitzar els factors d'impacte fins a fa una
dècada quan van començar a ser usats com una alternativa
per a calcular les freqüències esperades de cites a articles publicats
recentmentuna aplicació molt polèmica de la cienciometria
com eina per avaluar institucions i científics. L'inventor
de l'SCI, i la seva base de dades companya, l'SSCI, examinarà
la seva història i discutirà el seu ús més recent en la visualització
gràfica de microhistories de temes acadèmics. Mitjançant
HistCite, un programari patentat per a l'anàlisi historiogràfic algorítmic,
es parlarà sobre la genealogia del descobriment de
Watson-Crick de la estructura de la doble hèlix del DNA i la
seva relació amb el treball de Heidelberger, Avery i altres.The Science Citation Index was proposed over 50
years ago to facilitate the dissemination and retrieval of scientific
literature. Its unique search engine, based on citation
searching, was not widely adopted until it was made available
online in 1972. Its by product, Journal Citation Reports, became
available in 1975 and included its rankings by impact
factor. Impact factors were not widely implemented until about
a decade ago, when they began to be used as surrogates for
expected citation frequencies for recently published papersa
highly controversial application of scientometrics in evaluating
scientists and institutions. Here, the inventor of both the SCI
and its companion, Social Sciences Citation Index, review the
history of these instruments and discusses their more recent
use in graphically visualizing microhistories of scholarly topics.
In an example thereof, the patented HistCite software for algorithmic
historiographic analysis is used to follow the genealogy
of the Watson-Crick discovery of the double-helix structure of
DNA and its relationship to the work of Heidelberger, Avery,
and others

Garfield, Eugene

Hemeroteca Cientifica Catalana

PERSPECTIVES The evolution of the Science Citation IndexIntroductionThe Science Citation Index (SCI®) was first promulgated inScience in 1955, as an up-to-date tool to facilitate the dissem-ination and retrieval of scientific literature [3]. Its practicalrealization was possible thanks to the already-existing infor-mation service, Current Contents. The early computer hadmade it feasible for Current Contents to appear each weektogether with its title word indexes and author address direc-tory. In those days, conventional indexes were anywherefrom six months to three years behind the literature.Nevertheless, the SCI’s success did not stem from its primaryfunction as a search engine, but from its use as an instrumentfor measuring scientific productivity, made possible by theadvent of its by-product, the SCI Journal Citation Reports(JCR) and its Impact Factor rankings. The SCI’s multidisciplinary database has two purposes:first, to identify what each scientist has published, and sec-ond, where and how often the papers by that scientist arecited. Hence, the SCI has always been divided into twoauthor-based parts: the Source Author Index and the CitationIndex. By extension, one can also determine what each insti-tution and country has published and how often their papersare cited. The Web of Science® (WoS)—the SCI’s electronicversion—links these two functions: an author’s publicationcan be listed by chronology, by journal, or by citation fre-quency. It also allows searching for scientists who have pub-lished over a given period of years. As an example of this,Table 1 shows the resulting list for a search of scientists whohave published for 70 to 85 years.A key question often arises as to the ability of citationindexing to retrieve all the relevant work on a topic. Beforethe advent of molecular biology, citation practices were notnearly as standardized as they are today, and implicit citationwas quite common, therefore, explicit citation of earlier rele-vant work could not always be found. When the ScienceCitation Index was launched in 1964, Irvin Sher and I hadalready begun using bibliographic citations to create topolog-ical maps which we called Historiographs, to investigatewhether citation indexes could aid in writing mini-historiesof scientific topics. More recently, gigabyte computer mem-ories made it possible to write a program called HistCite,which accepts the output of a WoS search and automaticallygenerates historiographs [www.histcite.com]. By collectingall the relevant citing papers on a subject in a WoS search, thecollective memory of the citing authors produces a visualdescription of the topical history. Figure 1 shows a year-by-year historiograph created to track the implicit connectionbetween the 1953 Watson-Crick paper on the double helix,and the 1944 work of Avery et al. on pneumococcal DNA(which Watson and Crick did not cite in their paper) [http://garfield.library.upenn.edu/histcomp/index-watson-crick.html].The Annual SCI Journal Citation Reports were officiallylaunched in 1975. The JCR evolved to provide a statisticalsummation of the Journal Citation Index, which in turn was theresult of re-sorting the Author Citation Index: instead of alpha-betizing the file by author name, you simply sorted the file bythe names of the journals in which papers were published.When this exercise was first performed in the early 1960s, thejournals already covered in Current Contents included thosethat either produced the most papers or those that were citedthe most. But a simple method was needed to compare largejournals such as Nature, Science, and JAMA with smaller butimportant review and specialty journals including the AnnualReviews, which might not be selected if only total publicationEugene GarfieldChairman Emeritus, Thomson Scientific ISI Philadelphia, Pennsylvania, USAINTERNATIONAL MICROBIOLOGY (2007) 10:65-69DOI: 10.2436/20.1501.01.10  ISSN: 1139-6709 www.im.microbios.org E-mail: garfield@codex.cis.upenn.eduThis article is based on a lecture given by the author at the Institute forCatalan Studies, Barcelona, on January 24, 2007.For full text see URL http://garfield.library.upenn.edu/papers/barcelona2007.pdf 66 INT. MICROBIOL. Vol. 10, 2007or citation counts were taken into account [2], thus the journal“impact factor” was created. We observed that 25% of all cita-tions in the current year’s literature were to papers that wereonly two to three years old and so it was decided upon to usethe prior two cited years as the basis for calculating a currentyear impact factor—the average number of citations per pub-lished paper. The term “impact factor” has gradually evolved,especially in Europe, to describe both journal and authorimpact. Whereas an individual author produces a small num-ber of articles on average (although there are some phenome-nally productive ones), journal impact factors generallyinvolve relatively large populations of articles and citations. Ajournal’s impact factor is based on two elements: the numera-tor, which is the number of cites in the current year to anyitems published in the journal during the previous two years;and the denominator, the number of substantive articles(source items) published during the same two years. Theimpact factor could just as easily be based on the previousyear’s articles alone, which would give even greater weight torapidly changing fields or, take into account longer periods ofcitations and/or sources, but the measure would be less current.It is important to take into account that correspondence, letters,news stories, obituaries, editorials, interviews, and tributes arenot included in JCR’s calculation of source items. Never-theless, since the numerator includes citations to these moreephemeral items, some distortion will result; but ordinarily justa small number of journals will be affected, and out of those,the effect will imply a change of only 5–10% [4]. Scientometrics and journalologyCitation analysis has blossomed over the past three decadesinto the field of scientometrics, already possessing a special-ized journal which started in 1978, Scientometrics, and itsown International Society of Scientometrics and Informetrics(ISSI) [http://www.issi-society.info]. Over 15 years ago, SteveLock aptly named the application of scientometrics to journalevaluation “journalology” [10]. All citation studies should be normalized to take intoaccount variables such as discipline, half-life, and citationdensity [12]. The half-life (number of retrospective yearsrequired to find 50% of the cited references) is longer for aphysiology journal than that for a physics journal. For somefields, JCR’s two-year based impact factors may or may notgive as complete a picture as would a five- or ten-year period.Nevertheless, when journals are studied within disciplinarycategories, the rankings based on 1-, 7- or 15-year impact fac-tors do not differ significantly [6,7]. The citation density isthe average number of references cited per source article.Citation density (R/S) is significantly lower for mathematicsjournals than for molecular biology journals. There is a wide-spread but mistaken belief that the size of the scientific com-munity that a journal serves significantly affects the journal’simpact factor. This assumption overlooks the fact that whilemost authors produce more citations, these must be shared bya larger number of cited articles. Most articles in most fieldsGARFIELDTable 1. Scientists who have published for 69 years or moreScientist Birth/Death Pub Years Years PubIzaak Maurits (Piet) Kolthoff (analytical chemist)Michael Heidelberger (organic chemist–immunologist)Melvin Guy Mellon (chemist)Ernst Mayr (geneticist)Michel Eugene Chevreul (chemist)Carl S. Marvel (polymer chemist)Joel H. Hildebrand (chemist)Linus Pauling (chemist)John Carew Eccles (neurophysiologist)Donald Coxeter (mathematician)Charles Scott Sherrington (physiologist)Hans Albrecht Bethe (physicist)Alexander Kossiakoff (engineer; guided missile expert)Norman Hackerman (chemist)Michael DeBakey (cardiac surgeon)Gerhard Herzberg (chemist)Herman Mark (polymer chemist)1894-19931888-19911893-19931904-20051786-18891894-19881881-19831901-19941903-19971907-20031857-19521906-20051914-2005191219081904-19991895-19921917-20021909-19931920-20031923-20051808-18891917-19961907-19831923-19981929-19921930-20011882-19521934-20041935-20051936-20061937-20061924-19921922-1990868584838280777674727171717170696967INT. MICROBIOL. Vol. 10, 2007are not well cited, whereas some articles in small fields mayhave unusual impact, especially when they have cross-disci-plinary impact. The average number of citations per articleand the immediacy of the citations—and not the number ofauthors or articles in the field—are the significant elements[5]. The size of the field, however, will generally increase thenumber of “super-cited” papers. In addition to helping libraries decide which journals topurchase, journal impact factors are also used by authors todecide where to submit their articles. As a general rule, thejournals with high impact factors include the most presti-gious, although the perception of prestige is a murky subject.Librarians argue that the numerator in the impact-factor cal-culation is itself even more relevant. Bensman argues thatthis 2-year total citation count is a better guide to journal sig-nificance and cost-effectiveness than is the impact factor [1].Journal impact can also be useful in comparing expected andactual citation frequency. Thus, when ISI prepares a person-al citation report it provides data on the expected citationimpact not only for a particular journal but also for a parti-cular year, because impact factors can change year to year.It is well known that there is a skewed distribution of cita-tions in most fields: the 80/20 rule applies in that 20% of thearticles may account for 80% of the citations. On the onehand, some editors would like to see impact factors calculat-ed solely on the basis of their most-cited papers so that theirotherwise low impact factors can be ignored. Others wouldlike to see rankings by geographic area because of SCI’salleged English language bias. Europhiles would like to beable to compare their journals by language or geographicgroups especially in the social sciences and humanities. Otherobjections to impact factors are related to the system used inJCR to categorize journals. In a perfect system it ought to bepossible to compare journals with an identical profile. But infact, there are rarely two journals with identical semantic orbibliographic profiles. ISI’s heuristic, somewhat subjectivemethods for categorizing journals are by no means perfect,even though their specialists do use citation analysis to sup-port their decisions. There have been recent attempts to groupjournals more objectively, relying on two-way citational rela-tionships between journals to reduce the subjective influenceof journal titles [11], e.g., citation analysis proved that theSCIENCE CITATION INDEXFig. 1. Watson-Crick year-by-yearhistoriograph (1938–1955). [From:Garfield E, Pudovkin AI, Istomin VI(2003) Mapping the output of topicalsearches in the Web of Knowledge andthe case of Watson-Crick. InformationTechnology and Libraries 22:183-187]68 INT. MICROBIOL. Vol. 10, 2007Journal of Experimental Medicine was a leading immunologyjournal. The coefficient of relatedness between two journalsreflects how often a journal cites and is cited by each of thejournals it is compared to, and it takes into account the sizesof the journals involved (papers published) as well as thenumber of times each journal cites the other (Fig. 2). Many discrepancies with journal impact factors are elim-inated altogether in another ISI database called the JournalPerformance Indicators (JPI) [http://scientific.thomson.com/products/jpi]. This annual compilation now covers the peri-od 1981 to the current year. Unlike JCR, this database linkseach source item to its own unique citations, making impactcalculations more precise. Only citations to the substantiveitems are counted in the denominator, and it is possible toobtain cumulative impact measures covering longer timespans. Table 2 shows how the cumulated impact for JAMAarticles published in 1999 was 84.5. In this year, JAMA pub-lished 1905 items of which 630 were letters, and 253 editori-als; citations to these items were not included in the JPI cal-culation of impact. In spite of the alleged distortions intro-duced by counting citations to all “editorial” material in SCI,a recent report by González and Campanario at the Univer-sity of Alcalá (Spain) demonstrates that the effect, if any, isquite minor [8].The use of journal impact factors instead of actual articlecitation counts to evaluate individuals is a highly controver-sial issue. Granting and other policy agencies often wish tobypass the work involved in obtaining actual citation countsfor individual articles and authors. Since recently publishedarticles may not have had enough time to be cited, it is tempt-ing to use the journal impact factor as a surrogate evaluationtool. Presumably the mere acceptance of the paper for publi-cation by a high impact journal is an implied indicator of pres-tige. Typically, when the author’s recent bibliography isexamined, the impact factors of the journals involved are sub-stituted in lieu of the actual citation count. This practice beganabout a decade ago, when administrators decided they wouldestimate the future impact of a recently published paper byincorporating the impact factor for the journal in which thepaper is published. (For younger scientists, especially, manyof the papers listed in their CV have been published often dur-ing the period used to calculate impact, and most of them willnot be cited for a few years or more, depending upon the rateat which research on their topic progresses.) Thus, the impactfactor is used to estimate the expected influence of individualpapers, a rather dubious practice taking into account the afore-mentioned skewness observed for most journals. Today, so-called “webometrics” are increasingly broughtinto play, though there is little evidence that this is any betterthan traditional citation analysis. Web “sitations” may occura little earlier, but they are not the same as citations. Thus,one must distinguish between readership or downloading,and actual citation in new research papers. Nevertheless,some studies seem to indicate that web sitation is a harbingerof future citation. The assumption that the impact of recent articles cannotbe evaluated in SCI is not universally correct. While theremay be several years delay on some topics, papers thatachieve high impact are usually cited within months of pub-lication and certainly within a year or so. This pattern ofimmediacy has enable ISI to identify “hot papers” in itsbimonthly publication Science Watch. However, full confir-mation of high impact is generally obtained two years later.The Scientist magazine waits up to two years to select “hotpapers” for commentary by authors, yet most of these paperswill eventually go on to become citation classics [http://www.citationclassics.org].Of the many conflicting opinions about impact factors,Hoeffel expressed the situation succinctly: “Impact factor isnot a perfect tool to measure the quality of articles but thereGARFIELDFig. 2. General formula for calculating citationrelatedness between two journals and the relat-edness coefficient expressing the average of themaximum and the minimum.69INT. MICROBIOL. Vol. 10, 2007is nothing better and it has the advantage of already being inexistence and is, therefore, a good technique for scientificevaluation. Experience has shown that in each specialty thebest journals are those in which it is most difficult to havean article accepted, and these are the journals that have ahigher impact factor. Most of these journals existed longbefore the impact factor was devised. The use of impact fac-tor as a measure of quality is widespread because it fits wellwith the opinion we have in each field of the best journalsin our specialty. [9]”Obviously, a better evaluation system would involve actu-ally reading each article for quality, but even then difficultiesof reconciling peer review judgments would arise. When itcomes to evaluating faculty, most people do not have or careto take the time any more. Even if they did, their judgmentwould surely be tempered by observing the comments of thosewho have cited the work; this is known as citation contextanalysis. Fortunately, in the near future, full-text capabilities inthe web will make this a more practical task to perform. References1. Bensman SJ, Wilder SJ (1998) Scientific and technical serials holdingsoptimization in an inefficient market: a LSU serials redesign projectexercise. Library Resources and Technical Services 42:147-2422. Brodman E (1944) Choosing physiology journals. Bull Med LibraryAssociation 32:479-4833. Garfield E (1955) Citation indexes for science: a new dimension in doc-umentation through association of ideas. Science 122:108-1114. Garfield E (1972) Citation analysis as a tool in journal evaluation.Science 178:471-479. Reprinted in Current Contents No. 6 pp 5-6 (1973);Essays of an Information Scientist (1977) vol 1, pp 527-5445. Garfield E (1976) Is the ration between number of citations and publica-tions cited a true constant? Current Contents No. 6 pp 5-7. Reprinted inEssays of an Information Scientist (1977) ISI Press, Philadelphia, vol 2,pp 419-4216. Garfield E (1998) Long-term vs. short-term journal impact: Does it mat-ter? The Scientist (February 2) 12(3):10-12 [www.the-scientist.library.upenn.edu/yr1998/feb/research_980202.html]7. Garfield E (1998) Long-term vs. short-term journal impact: Does it mat-ter? (part II) The Scientist (July 6) 12(14):12-13 [www.the-scientist.library.upenn.edu/yr1998/july/research_980706.html]8. González L, Campanario M (2006) Structure of the impact factor ofjournals included in the Social Sciences Citation Index: Citations fromdocuments labeled “editorial material”. J Am Soc Infor Sci Technol58:252-2629. Hoeffel C (1998) Journal Impact Factors (letter). Allergy 53:122510. Lock SP (1989) Journalology: Are quotes needed? CBE Views 12:57-5911. Pudovkin AI, Garfield E (2002) Algorithmic procedure for findingsemantically related journals. J Am Soc Infor Sci Technol 53:1113-111912. Pudovkin AI, Garfield E (2004) Rank-normalized impact factor: a wayto compare journal performance across subject categories. AnnualMeeting, Providence, RI. November 17, 2004. Published in Proceedingsof the 67th Annual Meeting of the Am Soc Infor Sci Technol, vol 41, pp507-515SCIENCE CITATION INDEXTable 2. JPI data on JAMA. Citation impact (all items) in one year periods,1981 to 2004 [from ISI Journal Performance Indicators file, 2004]Rank Year Impact Citations Papers12345678910111213141516171819202122232419811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200429.5735,5340.1135.2635.0548.7644.7048.4055.7954.8347.1958.4865.5570.5481.9960.1658.1975.2084.48a56.7149.9842.8419.093.3416,29120,35822,21921,79118,43624,57626,68830,00934,97935,96830,38934,38938,34939,14845,09432,90832,82137,37231,25721,04018,84216,92173111174551573554618526504597620627656644588585555550547564497370371377395383351aImpact calculation: 31,257 / 370 = citations received from 1999 to 2004 / articles published inJAMA in 1999 = 84.5

The evolution of the Science Citation Index

Revistes Catalanes amb Accés Obert

The Evolution of the Science Citation Index

El Science Citation Index (SCI) va ser proposat fa més
de 50 anys per facilitar la disseminació i recuperació de literatura
científica. El seu cercador era únic pel fet de basar-se en una
recerca per cites, però no va ser àmpliament adoptat fins que
va estar disponible en la xarxa en l'any 1972. El Journal Citation
Reports, que apareix com a conseqüència d'aquest en
1975, incloïa a més una classificació basada en el factor d'impacte.
No era comú utilitzar els factors d'impacte fins a fa una
dècada quan van començar a ser usats com una alternativa
per a calcular les freqüències esperades de cites a articles publicats
recentmentuna aplicació molt polèmica de la cienciometria
com eina per avaluar institucions i científics. L'inventor
de l'SCI, i la seva base de dades companya, l'SSCI, examinarà
la seva història i discutirà el seu ús més recent en la visualització
gràfica de microhistories de temes acadèmics. Mitjançant
HistCite, un programari patentat per a l'anàlisi historiogràfic algorítmic,
es parlarà sobre la genealogia del descobriment de
Watson-Crick de la estructura de la doble hèlix del DNA i la
seva relació amb el treball de Heidelberger, Avery i altres.The Science Citation Index was proposed over 50
years ago to facilitate the dissemination and retrieval of scientific
literature. Its unique search engine, based on citation
searching, was not widely adopted until it was made available
online in 1972. Its by product, Journal Citation Reports, became
available in 1975 and included its rankings by impact
factor. Impact factors were not widely implemented until about
a decade ago, when they began to be used as surrogates for
expected citation frequencies for recently published papersa
highly controversial application of scientometrics in evaluating
scientists and institutions. Here, the inventor of both the SCI
and its companion, Social Sciences Citation Index, review the
history of these instruments and discusses their more recent
use in graphically visualizing microhistories of scholarly topics.
In an example thereof, the patented HistCite software for algorithmic
historiographic analysis is used to follow the genealogy
of the Watson-Crick discovery of the double-helix structure of
DNA and its relationship to the work of Heidelberger, Avery,
and others

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The Evolution of the Science Citation Index

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Revistes Catalanes amb Accés Obert

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