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Reprhsted from 6cleM% May 8, 1664, Vol. 144, No. 3619, pages 649-6S4Science Citation Index-

A New Dimension in IndexingThis unique approach underlies versatile bibliographic

systems for communicating and evaluating information.

Over a quarter of a century agoH. G. Wells made a magnificent, ifpremature, plea for the establishmentof a world information center, theWorld Brain (1). To Wells, the WorldBrain became the symbol of interna-tional intellectual cooperation in aworld at peace. The realization, with-in our lifetime, of the physical andintellectual achievement envisioned inWor/d Brain no longer lies in the realmof science fiction. The ultimate spec-ification for a World Brain must awaitmore fundamental studies and under-standing of information science. HOW-ever, the increasing convergence ofsuch previously unrelated fields as ge-netics, linguistics, psychology, andchemistry foretells exciting realign-ments in classical conceptions of theinformation problem. Unquestion-ably there are many different formsand arrangements which a Worlcf Braincould assume. Vannevar Bush~ Mem-ex was a microfilm version of theuniversal fingertip library (2): Memexstimulated considerable speculation butalso produced some realistic work (3).Tukeys Information Ledger is a re-cent specification of the desiderata fora universal information system (4).More recently, Senders has given anapproximate quantitative measure ofthe information content of the worldslibraries (5). Surely the increasingawareness of the science-informationproblem on the part of both the legis-

The author is director of the Institute for ScLeirtific Information. Philadelphia. and lecturerin information retrieval at -the University ofPsmssylvania.

Eugene Garfieldlative (6) and executive (7) branchesof government will add momentum tothe inevitable trend toward establish-ment of a world information center.

The main purpose of this article isto provide some perspective on thescience-information, or sciencc-indcx-ing, problem: to review briefly thedevelopments in citation indexing thathave occurred over the past 10 years;and to indicate why the recently pub-lished Science Cifation Index (8) is aharbinger of things to comea fore-runner of the World Brain.

The average scientist thinks a WorldBrain would be extremely useful, Thepossibility of having all recordedknowledge at ones fingertips is fasci-nating. The librarian, however, emi-nently more practical on this topic thanthe scientist, because he has learnedto live with bibliographical poverty inthe midst of scientific wealth, thinks ofthe enormously detailed problems ofbibliographic control (9). Therefore,the librarian may be the one who bestappreciates the implications of the Sci-em-e Ci/a/iorr Index for bibliographiccontrol. It is the first really seriousattempt at universal bibliographicalcontrol of science literature since theturn of the century (10), On the otherhand, tbe librarian is sometimes tooacutely aware of the detailed problemsinvolved in compiling an internationalinventory of scienceprecisely whatthe Science Citation Index is. I believethe need for such an inventory, forsuch bibliographic control, is indisput-able (11).

Whether or not citation indexes areuseful is a question that has now been

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,answered. We have enough favorableexperience in using them to know theyare desirable and useful. However. acitation index must meet the same eco-nomic test that all products in oursociety must meet: Does the cost justifythe benefits? To measure its value tothe scientific community is not simple.Do the cost and difficulties of retrievingpertinent literature justify bypassingthe literature and chancing a replica-tion of research? Or, as Maddox re-cently phrased the problem: Is theliterature worth keeping? (12). TheWeinberg Committee (7) maintainsthat the literature is an integral partof the research process. Printed tom-munication still has a long life expect-ancy as a means of imparting currentinformation and retrieving data; it willbe with us at least until we have de-veloped science communication to thepoint where all indexes, journals,books, and other printed media be-come obsolete and a World Brain takesover. Meanwhile, the initial biblio-graphic control necessary for establish-ing a World Brain is economically justi-fied by the immediate and interimrequirements of tbe expanding com-plex of science and technology.

If we ever achieve total communi-cation, a state of research nirvana,then an enormous time-shared, random-access computer memory will augmentmans finite memory and replace print-ed indexes and catalogs. In this condi-tion of nirvanu a World Brain will it-self have become an auxiliary tomans own brain, Or, as Bernal hasstated it (/3), The speculations of thefuture may then be the speculations,not of one man or of many men, butof all humtinity and their machines.But this achieven]ent will require a fargreater commitment to the task ofaccumulating and communicating sci-entific information than we have everbeen willing to make previously. Inany event, the direct linking of con-ceptual information which is made pos-sible for the first time through citation

indexing will be a vital part of suchtotal communication.

An E xampleIn June 1955 a paper appeared in

Science entitled Citation indexes forscience (14): it was in part based onsuggestions made by Adair (/5) andHart (/6). In 1957 there followed apaper on the applicability of the ci-tator system to patents (1 7), whichcited Hart (16) and Seidel (/8) insupport of arguments for establishing acitation index to patents. In two SU)-sequent papers (19, 20) the a priorinature of conventional indexes was dis-cussed in contrast to the a posterioricharacter of citation indexing. The re-lationship of the citation index to theproblem of achieving a Unified ScienceIndex was explored at the InternationalConference on Scientific Information in1958 (21). Fano (22), Ernst (23),Tukey (24), Savage (25), Lipetz (26),Kessler (27, 28), Atherton (29), andSalton (30) have also pursued variousramifications and possibilities of cita-tion indexing.

The foregoing bibliographic recapit-ulation is intended to emphasize, to thereader unfamiliar with citation indexes,both the advantages and the simplicityof citation indexing. The 17 paperscited in the preceding paragraph areassociated here in this article. A cita-tion index would automatically lead tbeuser to this group of related works,provided he knew of any one of thecited references. With a citation index,this article and the paragraph in ques-tion would be retrieved regardless ofthe date or the journals in which thecited papers originally appeared. Thescatter of the 17 references, however,also illustrates some of the complexi-ties of compiling citation indexes. Thepreceding paragraph is a historical-bibliographic introduction comparableto that provided by many authors inwriting scientific papers.

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Consider the reader who has neverheard the term cilahn index but wantsinformation on this topic. His diffi-culties in finding the article you arenow reading will illustrate the difficul-ties of finding information by conven-tional methods. It would be almostimpossible for one unfamiliar with thecitation-index concept to search for pa-pers under the heading citation in.dexing because the term probablywould not occur to him. If the ideaof citation indexing did occur to him,the descriptive terminology that he se-lected in searching for the citation-index idea would probably have beendifferent. And yet, previous knowledgeof any one of the references cited inthis article, or cited in any of the other17 citation-index papers, would,through the use. of citation indexes,bring to the attention of the requesterthis new concept. Even in this cir-cuitous example there is no paradoxinvolved in calling the results of thesearch a new concept, since theactual search could have been per-formed by some other person using acitation index, while the requester him-self remained unaware of its existence.Thus, interest in Vannevar Bushs pa-per (2), Avakians work (3), or anyother of the 17 cited references whichis relevant to, but does not specificallyname, citation indexing would open thedoor to the idea of citation indexing.

Consider the class of readers whomight have thought about the ideaof a citation index prior to publicationof this article. They fall into two sub-classesthose who might have calledit a citation index or something roughlyequivalent, such as a reference indexor citator, and those who might not.The latter subclass includes Fano (22)and Ernst (23), whose linguistic con-ception of the citation-index idea wasquite different from mine, though theend result was essentially the same.The semantic difference lies in mythinking of a citation index primarilyas a printed index, whereas they visu-alized a machine index. This manipu-

lative difference in no way alters thebasic commonality of the two systems.The information processed in the twois exactly the same-citations appear-ing in bibliographies.

To continue our examplethe litera-ture searcher interested in finding pub-lished articles on the citation indexby conventional methods faces a basi-cally difficult task. Even though hemay have the terminology correct, ornearly correct, he will find that Scienceis one of those journals that is .se/ec-fively indexed by the leading discipline-oriented indexing services, Chemicalarticles are indexed by Chemical A b-stracls, physical articles by ScienceA bsfracts, biological articles by f?i-ological A bstracts, and so on. But evenif one assumes that the conventionalindexing services do abstract articlessuch as this, an additional degree ofuncertainty is then introduced by thepossibility (and too often the prob-ability) that either the indexer or thesearcher did not use the correctterminology. Concepts or ideas are ex-tremely difficult to handle consistentlyin classical subject indexes.

For the other papers in the list of17 citations, effective selection and in-dexing treatment by the conventionalindexing and abstracting services iseven more unlikely than it is for thecited article from Science ( 14). Thearticle in the Journa/ of the Pa/enrOfice Society ( 17) illustrates one ofthe many serious deficiencies of ourfragmented. discipline-oriented index-ing activities (31 ). That paper, onindexing chemical patents, was pub-lished in a legal journal, and thusthe audience of librarians andchemists who might be interested inthe paper was sacrificed for an audienceof patent attorneys. The situation iseven worse with respect to references20 and 21, both of which are partof the published proceedings of a con-ference. Hanson and Jones have shownthat most papers appearing in the pub-lished proceedings of conferences arenever indexed (.32). Since the number

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of published conference proceedings isquite large, a considerable amount ofimportant literature would be buried ifthe participants in these conferencesdid not cite the same papers in subse-quent articles, published in journalswhich are covered by indexing and ab-stracting services. This is reflected instudies by Touloukian et al. (33) whichshow that it is more efficient to usean indexing service to locate a fewrecent papers and then search bibliog-raphies in these papers than it is tosearch the indexes exclusively.

The conventional disciplin&orientedindexes thus leave much to be desiredwith respect to breadth of coverageand as means of indexing consistentlyand by concept. If, instead of search-ing for papers on the subject of citationindexes, the reader seeks papers on anyone of dozens of interdisciplinary sub-jects investigated today, without know-ing the exact headings under whichthey are indexed, he encounters similardifficulties. This will be apparent if,for example, he tries to compile rap-idly a bibliography on one of the fol-lowing topics: theories on the originof life: nucleic acid staining techniques;applications of computers to biomedi-cal research.

What 1s a Citation Index?A citation index is an ordered list

of cited articles each of which is ac-companied by a list of citing articles.The citing article is identified by asource citation, the cited article by areference citation. The index is ar-ranged by reference citations. Anysource citation may subsequently be-come a reference citation. At the timeof indexing, the article you are nowreading would be considered a source.In that case it would appear in thecitation index under all the referencecitations in References and notes atthe end of the article. It would alsoappear in the source index which ac-companies the citation index proper.

The description of a citation indexdoes not imply a particular order forthe list of cited references. We havestudied in great detail the many waysone can arrange a citation index. Theseinclude arrangement by author, jour-nal, year, document serial number, VOl-ume, page, or other parameter. Anyfragment of the usual citation mightbe the basis for organizing a citationindex. The decision to arrange the Sci-ence Citotion Index (8) by author wasbased on a total-systems study in whichit was determined that the typical userrequirement is to find what sources havecited a particular reference, albeit attimes the reference citation is incom-pletely recollected. Our studies havealso shown the desirability of provid-ing, with the citation index, a com-plete source index containing fullsource-article titles and certain addi-tional data. This source index is simi-lar to an upgraded conventional authorindex covering all disciplinesthe firstobjective of the Unified Science Index(2/). Arrangement by author is fa-vored in the citation index and thesource index because the research sci-entist usually approaches the literaturefirst by author.

By using a citation index one deter-mines what subsequent papers have cit-ed a particular reference. How wouldthe new citation index help you findarticles on the subject citation index?I have already shown why it would bedifficult to find these with conventionalsubject indexes. Suppose you havefound, by chance, the article by Adair(}5) by scanning back volumes of,4merican Documentationa not un-likely supposition for someone interest-ed in finding such information. whenyou have located the Adair article bysuch browsing you look it up in acumulated citation index for the sourceyears 1955-64; the index immediatelytells you that at least seven papershave appeared on the subject since 195514, 17, 19, 21, 24, 26, and thearticle you are now readingall citing

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Adairs paper! However, this is onlythe beginning, By a technique calledcycling you can quickly find the otherpapers on the subject of citation in-dexes, as weIl as others related to theuse of citations. Cycling means ex-amining the bibliographies of the pa-pers you start with, and of the sourcepapers obtained, in order to locate ad-ditional relevant works. By looking upthe latter in the citation index youfind new citing sources.

For example, in my paper in theChemical Bulletin (19) the letter bySchoenbach, in which he criticizes ci-tat ion indexing, is cited (34). Schoen-baths paper in turn refers to my origi-nal paper (14), which, through the ci-tation index, leads to my reply (35).Furthermore, by successively checkingon whether the source articles whichcited Adair have themselves appearedlater as cited references and followingup any secondary sources so located,one quickly generates a complete bibli-ography.

As the literature of a field increases,the redundancy in bibliographies makesit easier to up-date the search, no mat-ter which of various related articles islocated first. This redundancy also re-duces loss of information in the cita-tion index through typographical or oth-er errors, including the omission, un-witting or otherwise, of relevant refer-ences by authors.

How can we assume that a searcherwill find any of the necessary articlesto begin his search? The user of thecitation index must have a startingpoint. Here is a major difference be-tween conventional subject indexes andcitation indexes.

Proponents of conventional language-oriented subject indexes implicitly as-sume that the typical reader does notknow of any papers on the subject heis investigating. How often is this trueof the working scientist? More often,perhaps, it is a librarian or student whoseeks information without prior knowl-edge of the subject. If the user does

not know of a previous work on thesubject he must find one through abook, an encyclopedia, or a colleague.These can usually supply one or morestarting references. If there is little ornothing written on the subject the userwill have a difficult time no matterwhat he does, as no literature searchcan turn up what doesnt exist!

Too Many Citations or Too Few?Although the average published pa-

per is cited less than once each year,certain papers are very frequently cited.To take an extreme case, the papermost frequent] y cited in 1961 wascited over 500 times (36). While, bymost search standards, this makes a longlist of citing papers to scan, even thisnumber is not one bit excessive for thechemist, sociologist, or historian in-terested in writing a complete reviewor evaluation of the method cited.Moreover, several of the citing pa-pers introduced procedural modifica-tions.

It is frequently assumed that theusual citation practices lead to an isn-practical number of sources for a par-ticular reference. In rare instances thismay be true, but, as we have seen,for certain purposes the searcher maybe only too glad to have a rich andcomprehensive bibliography to scan, Ex-perience shows, however, that the num-ber of sources uncovered is in mostcases quite manageable. Furthermore,the yield of sources can be reduced byvarious simple means whenever this isrequired. One such method involves theuse of bibliographic coupling (28).

In designing the Science Citation in-dex (8) it was assumed that the usercould specify one or more referencesas starting points. It may sometimes benecessary or desirable to start withmore than one reference. In these casesthe searcher can cull the sources bylooking up in the index only thosesources which cite two or more of the

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starting references. This is the essenceof bibliographic coupling. Or sourcesmay be selected or rejected on thebasis of authorship, journal title, articletitle, number of references, type ofarticle, date of publication, and classi-fication numbers.

The refining of a search result bythese methods is generally quite un-necessary. In an annual cumulationcomprising 1.4 million references (37),the average number of citing sourcesper reference cited was found to beabout 1.5. It is easy to lose sight of thefact that, contrary to the general clich6that there is too much scientific infor-mation, there is often little or no infor-mation available on a specific point(38). The number of references citedeach year is a function of the sizeof the current and past literature andof the writing habits of the authors.However, it is interesting to note thatthe average number of citing sourcesper ~ference cited did not change ap-preciably once we exceeded a criticallevel of several hundred key journals.

In day-to-day research, the citationindex will also provide the scientistwith useful leads toward an unspecifiedinformation objective. Frequently thescientist-user of indexes does not havea precise objective in mind. He is simplyexploring information pathways that ap-pear to be exciting and interesting. Thecitation index facilitates this browsingprocess. On the other hand, the com-petitive nature of modern research (39)often involves him in negative Iiterat weresearch. Many persons legitimatelyhope they will not find pertinent ref-erencesas, for example, in patentsearches. In evaluating the citation in-dex and other indexes one must con-sider the ease with which one can ob-tain a negative result with a high de-gree of certainty.

Obviously citation indexes will be ef-fective only to the extent that the bib-liographies in published papers are ac-curate reflections of the earlier litera-ture. In evaluating papers submitted to

journals, referees should determinewhether all pertinent references havebeen provided. The citation index willsignificantly assist the referee in identi-fying such pertinent references. A pa-per recently reported as novel a methodof analyzing for peptides (40), eventhough the same work had been re-ported 4 years earlier (41). There isno question that, had the authors orreferees had access to a citation in-dex, the second paper would not havebeen published, and the subsequent cor-rection (42) would have been unneces-sary. The two papers (40, 41) con-tained four references in common; fromany one of these the earlier work couldhave been pinpointed through the cita-tion index. Our files contain numerousexamples of this type.

How serious is the problem of non-citation of pertinent references, forwhatever reason, by authors? Most ofus have seen examples of what ap-pears to be an obvious omission of areference to a related piece of work byanother author. Such omissions will un-doubtedly affect the utility of the cita-tion index for current awarenesssearches. How much cannot yet be de-termined. The fact that papers whichdo not cite the earlier Literature willnot be retrieved directly through cita-tion indexing may exert some influenceon authors in the future. However,most papers do contain pertinent bibli-ographies, and, in time, most papers arecited a few times. It is a rare paperwhich neither cites nor is cited. How-ever, editors and referees, in acceptingor recommending acceptance of a pa-per, might insist that certain standardsof literature search be met by theauthor, just as similar standards are as-sumed by anyone applying for a patent.References in patents, however, are sup-plied by the referee (examiner), not theauthor (inventor).Disseminat ion P rob lem

I have discussed some of the waysin which the citation index can be used

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to search literature. If a printed listof sources which cite a particular ref-erence is of use, then a service, throughwhich such citations, or the articlesthemselves, are automatically and selec-tively disseminated, will also be useful.It is easier to decide how relevant aciting paper is by quickly scanning thepaper itself than by reading a title or anabstract. Through such scanning thestarting reference can be considered incontext within the source article. Thisstep is aided by the fact that mostcitations are enumerated and easilytraced within the body of the text. Asentence or paragraph thus disclosedmay contain vital information whichhad been completely ignored by anabstracter or subject indexer. The de-sign of just such an automatic weeklyalerting service has been completed,and indications are that it will sig-nificantly aid the individual in keepingabreast of his specific interests, as de-fined by his pertinent question cita-tions.E xten sion s in to Su bject In dexh sg

What are the possibilities of usingthe citation index in conjunction withconventional indexing? In discussions ofcitation indexes at the Dorking Con-ference (20) it was correctly concludedthat each reference citation is a form ofindex heading or descriptor. A simi-lar conclusion was implied in the state-ment that each author indexes hisown papers each time he cites anotherpaper (14). Now, let us assume thatthe ideas expressed in a particularsource article are reflected in the indexheadings used by some conventional in-dexing system. In that case, a displayof the descriptors or subject headingsassigned to that paper by the indexerconstitutes a restatement of the subjectmatter of that paper in the indexersterminology. When the indexing is au-tomatic and based on article titles, thenthe key words restate the title andpresumably restate the main subjects ofthe paper, Suppose you now collect and

examine the array of descriptors gen-erated by all the references cited in aparticular source paper, How accurate-ly will this list of descriptors describethe contents of the source document?Some preliminary experiments have re-vealed that the terms selected in index-ing a source paper corresponded closelywith those used to index rhe referencecitations. The combined array of de-scriptors for all cited articles character-ized the subject matter of the sourcearticle in great detail. There are cer-tain exceptions; for example, the no-menclature used to index a previouslyincompletely described drug is inade-quate for the subsequently completelyidentified chemical structure.

The implications and ramifications ofthese experiments may prove valuableboth in future conventional cerebral in-dexing and in computer indexing. First,the speed and consistency of conven-tional indexing would be increased ifone could quickly display (by means ofcomputer methods) the earlier indexingterms assigned to the references in aparticular source article being indexed.This idea was implicit in the PhficoMedlars proposal (43), in which itwas suggested that the indexer would becapable of direct communication (on-line) with the computer. It was alsoimplied in Fanos matrix, in whichthe degree of relevance of two docu-ments is determined by comparing thelists of reference citations. In Fanossystem, two documents would be con-sidered identical if the lists of biblio-graphical citations were identical. Thisis a specific case of the more generalaxiom that two documents are indis-tinguishable within any retrieval systemif all of the assigned descriptors are thesame (44). The only way the docu-ments can be differentiated is by theassignment of additional descriptorsthat is, by indexing in greater depth.Machine Citation Index

If the same magnetic-tape files thatare. used to prepare the nonmanipula-

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tive printed citation index were searchedby computer, papers could be associat-ed through machine examination of thedescriptor patterns of cited papers. Inthis way one could incorporate andutilize existing indexing of earlier pa-persinmechanically evaluating the rele-vance of source papers.

The machine citation index would al-so facilitate studies on why certain pa-pers are never cited. Kessler reportsthe existence of a large number of suchpapers (27). What does this signify?Many factors can contribute to a lackof citations. In addition to the obviouspossibility that a paper is relativelyworthless, several information conceptscome into play. For example, informa-tion may remain untransmitted if anarticle has been published in a relative-ly obscure journal, in a journal general-ly devoted to a~icles in a very differentfield, or in a language or jargon foreignto potential users. The article may bedry or very long, and thus not widelyread. A poorly selected title or bibliog-raphy, or both, can also lessen citationof an article. However there is another,and challenging, factor: the timing ofa scientific article can be out of stepwith the general development of science-out of phase with the general com-munication network. The time lagcan be positive or negative, dependingupon the quality or originality of themessage. Like mutant genes, an ideamay be before its timethat is, thesocial climate may not be right for itsacceptance (45).

A paper may be so far ahead of itstime that it is not appreciated or citedfor many years. Mendels experimentswith peas in his monastery garden,Flemings observations of bacterial lysisin mold-contaminated petri dishes, Pres-Seys reports of An Apparatuswhich . . . teaches all lay buried industy tomes for decades before theirvast significance for genetics, antimi-crobial therapy, and teaching machinesbecame widely recognized. Indeed, thehistory of science abounds with ex-

amples indicating that the scientificcommunity is incapable of quickly ab-sorbing radically new ideas or infor-mation. If we assume that the paperswhich have never been cited includethose which were ahead of their time,the citation index may afford a meansof ferreting out those papers whichmight deserve reevaluation, redissemi-nation, or even republication. One ex-periment contemplated at the Institutefor Scientific Information is the identi-fication of genetics papers which werenot cited in the Genetics Ci[a~ion in-dex (46). These would be reappraisedby experts with respect to possible re-vival value. It wo~ld be gratifying touncover some hitherto uncited papersburied in the literature which, in thelight of more recent scientific discover-ies, do deserve republication.

Citation Indexes andAbst ract ing Services

Recently Bennett (47) has reiteratedmy earlier recommendation that an in-dex to the abstracts in specialty jour-nals and to abstracts prepared by thesmaller abstracting services be compiled(21). Frequently these are abstractswhich include criticism. As such, theyconstitute original publications. Everyauthor should know of such critical ab-stracts of his papers. In literaturesearches, abstracts may serve in lieu ofthe original articles, particularly whenthe original article is in a foreign lan-guage, or when it is not readily avail-able. Citation indexes can be used tolocate these abstracts quickly and toidentify unabstracted articles (31).

Auth or Citation IndexA random-access computer memory

does not require special ordering fordata storage. In such memories the ar-bitrarily assigned data-addresses neednot be known to the user. By contrast,a printed citation index must have a

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logical order. An alphabetical arrange-ment of reference citations by citedauthor has definite advantages and dis-advantages. One advantage is that anauthor arrangement brings into prox-imity references to different works bythe same author. In any other arrange-ment, citations to the work of a singleauthor would be scattered. A furtheradvantage is that the user who re-members no more than the authorsname and the approximate year a paperwas published can still usually completehis search. With the author arrange-ment there is a small but distinct com-plication: the name of a cited authormay appear with different spellings indifferent journals. This problem is ag-gravated by the fact that the scientificliterature employs many languages, al-phabets, and transliterating systems. Forinstance, when names are transliteratedfrom English into Russian and thenback into English, the original spellingmay be lost. An American namedWheeler may come through this millas Viiler. Hilbert comes through as Gil-bert. Chinese names present even morebizarre examples. To make thingsworse, the Journal of fhe Chemical So-ciefy, and others, drop authors initialsin citations (48). A Reference toSmith, Proc. Chem. Sot. 1953, 1234,is adequate for most purposes. How-ever, specific identification of the authoris made difficult by this practice. Fortu-nately, only a small percentage of cita-tions present such problems, but thesedo increase the cost of processing andthe difficulties for the user. One solu-tion may ultimately be to prepare briefcontents pages, which contain, forevery journal ever published, standard-ized spel Iing of the authors names.The computer can then be used to re-place incomplete, incorrect, or variantspellings with this standardized form.The preparation of contents pages isalso a requisite for the mechanicalidentification of articles which havenever been cited, discussed earlier.

In compiling the Science Citation in-dex, an interim solution to the problem

of orthography has been to have thecomputer use less than the authors ful~name when first identifying two ormore references to the same citation,then to have the computer select onevariation of the cited name for use inthe index.

Another complication of the authorcitation index is the problem of multipleauthorship. If one expects to find cita-tions to all the work of a given author,then that author must appear as theprimary author in the citations, or theindex must contain cross references orduplicated entries for all co-authorsnames. The average number of authorsper paper now exceeds two (49). Tolist all co-authors in a printed author-citation index would approximately dou-ble its size. One partial solution to thiscost and space problem has been thecompilation of a separate bibliographyor index of source articles, with alljunior and senior authors listed. Prepa-ration of a cumulated cross-referencedfile based on this source index willeventually allow the user to quicklyidentify all the works to which a givenauthor contributed.

ConclusionThe availability of comprehensive

citation indexes now opens new roadsto the solution of numerous scientificand documentation problems. Citationindexing bypasses some of the limita-tions of classical subject indexing, andits techniques can be incorporated inthe existing communication system aswell as in the World Brain, whatevershape or form that may take. Produc-tion of citation indexes has become aneminently practicable procedure, andthe results of research on over 2 mil-lion citations lead to the conclusion thatwe cannot afford to neglect this uniqueand versatile instrument, in view ofthe accelerating tempo of moderninterdisciplinary scientific research. Themain objective for the immediate fl t-ture is to increase the coverage, in

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terms of chronology and number ofsource publications, so that we will havea relatively complete inventory of all

Referencesqnd Notes1. H. G, Wells, world Brain (Doubleday,Doran, Gaiden CiIY, NY., 1938).2. V. Bush, AS we may think, ~tlanl~cMonthly 176, 101 (July, 1945).3. E. A. Avakian and E. Garfield, AMFl8-the Automatic Microfilm Information Sys-

tem, Spec. Libraries 48, 145 ( 1956).4. J. W. Tukey, Keeping research in contactwith the literature: Citation Indices andbeyond, J. Chem. Dec. 2, 34 ( 1962).5. J. W. Senders, Information stora6e re-quirements for the contents of the worlds li-braries. Science 141, 1067 (1963).6.

1.

8.

9.

During the past 7 years numerous Senatehearings on the science-information problemhave been conducted by tbe Committeeon Government Operations, Subcommittee onReorganization and International Organiza-tions (Senator Hubert H. Humphrey, chair-man ). See, for example, Interagency CoordLnation o/ information (published pursuantto Senate Resolution 276, 87th Congress, 21Sept. 1%2) (Government Printing Office,Washington, D. C.. 1963). For the House ofRepresentatives, see, among others, NationalInformation Center [Hearings on HR. 1946before the Committee on Education and La-bor, Ad Hoc Subcommittee on ResearchData Processing and Information Retrieval(Roman Pucinski, chairman) ] (GovernmentPrinting Office. Washington. D.C., 1963).A. M, Weinberg ef al., Presidents ScienceAdvisory Committee, in Science, Govern-ment, and Information (Responsibilities ofthe Technical Community in the Transfer ofInformation ) (Government Printing Office,Washington, D.C ., 1963).E. Garfield and I. H. Sher, Science CtfafionIndex ( Institute for Scientific Information,Philadelphia. 1963).J. H, Shera and M. E. Egan, Eds,. Bib/io-

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13.

14.

graphic Organization ( Univ. of ChicagoPress. Chicago. 1951 ).K. 0. Murr;, History of some attempts toorganize bibliography internationally, inBibliographic Organization, J. H. Shera andM. E. Egan, Eds. ( Univ. of Chicago Press,Chicago, 1951 ), pp . 24-53.E. Garfield, statement and testimony, Hear-ings on H.R, 1946 of 19 July 1963 [seeNational Information Center (GovernmentPrinting Office, Washington. D. C.. 1963).PP. 226-2511.J. Maddox, Is the literature wosth keep-ig?v, Bu//. A/omfc Scientists 19, No. 9, 14(1963).J. D, Bernal, The place of speculation inmodem technology and science, in TheScientist Speculate>, 1. J. Good, Ed. (Heine-mann, London, 1963), pp . 11-28.E. Garfield. Citation indexes for science,*.$ciencc 122, 108 ( 1 955).15. W, C. Adair, Citation indexes for scientificliterature? Am. Dec. 6, 31 ( 1955).16. H, C. Hart, Re: Citation System forPatent Off ice, 1. Patent O~ce S0.2. 31, 714(1949).17. E. Garfield, Breaking the subject indexbarriera citation index for chemicalpatents, ibid. 39, 583 ( 1957).18. A. H, Seidel, Citation system for patentoffice, ib id . 31, 554 ( 1949).

s c ien t i f i c and related research. To dothis will require the support of theentire scientific community.19 . E. Garfield, Citation indexes-new paths toscientific knowledge. Chem. Bull. 43. No. 4.11 (1956). -20. , in Proceedings of the In(ernatlonalStudy Conference on Classification for ln-tormarion Retrieval (Pergamon. New York,

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34. U. H . Schncnbach, Citation indexes fo rscience, Science 123, 61 ( 1956).35. E. Garfield, Citation indexed for science.ibid., p. 62.36. 0. H. Lowry, Protein measurement withthe Folin phenol rea8ent, J. Biol. Chem. 193,265 (1951).37. E, Garfield, Citation indexes in sociologicaland historical research, Am. J30c. 14, 289(1963),38. S. Hemer, Technical informationtoo muchor 100 little? Sci. Monthly 83, 82 ( 1956).39. F. Reif, The competitive world of the purescientist, Science 134, 1957 ( 1%1).40. R. H. Mazur, B. W, Ellis, p, S, Camarah,A new reagent for detection of peptides,

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nucleotides, and other N-H-containing com-pounds on paper chromatograms, J. BioLChem. 237, 1619 (1962).41, D. P, Schwartz and M. J. Pallansch, Tert-butyl hypochlorite for detection of nitrog.enous compounds on chromatograms,Anal. Chem. 30, 219 (1958).42. Correction note, J. BIol. Cherrs. 237, 3315(1962).43. Proposal fcu MEDLARS (Philco Corpora-tion Computer Division, Willow Grove, Pa.,1961).44, E. Garfield, Information theory and otherquantitative factors in code design for docu-ment card systems, J. Chem. Dec. 1, 70(1961).45. H. Hoagland, Science and the new human-ism, Science 143, 11 I ( 1964); se e alSO E. G.

Boring, Dual role of the Zeitgeist in sci-entific creativity, SC(. ,440rr/h/y 80, 101(1955).46. E. Garfield and I. H. Sher, Gerrcflcs CitationIndex ( Institute for Scientific Information,Philadelphia, 1963 ) .47. G. Bennett, Current index to abstractingservices, Sci-Tech News 1S, 129 ( 1961 )48. Since preparation of this article I havebeen advised (personal communication,March 1964) by the editor of the Journalof the Chemical Sociefy, L. C. Cross, thatby the end of 1964 authors initials will beincluded in all reference citations.49. B. L. Clarke, Multiple authorship trendsin scientific papers, Science 143, 822 ( 1964).

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