We have seen so far that the techniques of controlled vocabulary searching, general browsing and focused browsing in classified bookstacks, and keyword searching each has distinct advantages and disadvantages. Each approach works very well in some situations, but very poorly in others. Still other means of gaining subject access to written records exist; one of the most important is citation searching. This approach, like the others, is potentially applicable in any subject area, and it, too, has both strengths and limitations.
In citation searching you must start with a known source—one that you’ve already identified—relevant to your topic. It may be a book, a journal article, a conference paper, a dissertation, a website, a technical report, or an unpublished manuscript—it can be any kind of knowledge record. Further, the date of the starting-point source is irrelevant: it can be something written last year or centuries ago. What a citation search will give you is a list of subsequent publications that cite the source in a footnote. The assumption is that a later work that cites an earlier one is probably talking about the same subject, or at least playing in the same intellectual ballpark. This is sometimes not true—a work can be cited in a context irrelevant to your interests—but such connections work often enough that you need to be aware of this search technique. The advantage here is that, unlike the situations with controlled vocabulary or keyword searches, you do not have to worry of about finding correct subject headings or cross-references or narrower terms, nor do you have to think up all of the keyword synonyms or variant phrases for expressing your topic. Citation searching allows you to do subject searches in a way that circumvents vocabulary problems entirely. All you need, in most searches of this kind, is the author’s name, which you’ve already identified, and the source’s title (or the title and date of the journal in which it appears).
It is useful to think of citation searching as a kind of mirror image of footnote chasing. If you’ve already found a good source on your topic, you will certainly look at its footnotes and bibliography for further references to extend your search to other relevant materials; that is just common sense. Remember, however, that in doing so you are essentially looking backward in time—that is, at previous sources published before your starting-point source. Citation searching, in contrast, takes you forward in time, to subsequent sources published after your source—and yet still conceptually connected to it. And so it is just as useful as footnote chasing, but comparatively few people do it because most do not know it is possible to pursue this kind of inquiry. You should make it a rule, however: whenever you find a good source, check to see if some other author has referred to that work by citing it in a subsequent article, book, or website.
Citation searching can now be done via several subscription databases; in such cases your result will usually be a list of academic journal articles—not books or Web pages—that reference your source. Considerable citation searching can now also be done on the open Internet; the results here will be lists of websites or digitized books and journal articles citing your starting point. We will first consider the subscription databases, available only through libraries, that enable you to do this kind of searching, since their results will always entail some kind of editorial vetting for quality.
The Web of Science database is published by Thomson Reuters. It is a combination of three main component parts: the Science Citation Index Expanded (SCI-EXPANDED, or just SCI), the Social Sciences Citation Index (SSCI), and the Arts & Humanities Citation Index (A&HCI). Collectively they cover about 13,500 journals in 45 languages, about two-thirds of which (8,600+ titles) are in the Science component. The SSCI, however, covers about 3,100 titles and the A&HCI about 1,700. (Three additional components, Book Citation Index, Conference Proceedings Citation Index, and Data Citation Index, will be discussed below.)
What is especially important to begin with is that the 13,500 journals that are covered represent the cream of the crop of academic journals in all subject areas. Thomson Reuters has some very sophisticated computer algorithms that enable them to identify which journals are being most frequently cited in the footnotes of other journals—and those are the titles they go after to index. Other databases (e.g., AnthopologyPlus, PsycINFO, MEDLINE) will provide more extensive coverage of many more journals in their respective fields, but Web of Science provides excellent selective coverage of the best journals in each area—and merges them in a way that allows cross-disciplinary searching of all at the same time. (It is possible, however, to limit one’s searches to only the SCI, SSCI, or A&HCI sections individually.)
These Web of Science databases were touched on in Chapter 5 because they also allow keyword searching (as well as related record searching, to be discussed in chapter 7). But it is worth looking at them in more detail.1
Science Citation Index Expanded currently provides abstract-level indexing of more than 8,600 journals; retrospective coverage extends back to 1900. (For the early decades, however, hundreds [rather than thousands] of titles are covered.) Major journals in all of these fields are indexed:
Acoustics, Agricultural Economics & Policy, Agricultural Engineering, Agriculture (Dairy & Animal Science), Agriculture (Multidisciplinary), Agriculture (Soil Science), Agronomy, Allergy, Anatomy & Morphology, Andrology, Anesthesiology, Astronomy & Astrophysics, Automation & Control Systems, Behavioral Sciences, Biochemical Research Methods, Biochemistry & Molecular Biology, Biodiversity Conservation, Biology, Biology (Miscellaneous), Biophysics, Biotechnology & Applied Microbiology, Cardiac & Cardiovascular Systems, Cell Biology, Chemistry (Analytical), Chemistry (Applied), Chemistry (Inorganic & Nuclear), Chemistry (Medicinal), Chemistry (Multidisciplinary), Chemistry (Organic), Chemistry (Physical), Clinical Neurology, Computer Science (Artificial Intelligence), Computer Science (Hardware & Architecture), Computer Science (Information Systems), Computer Science (Interdisciplinary Applications), Computer Science (Software Engineering), Computer Science (Theory & Methods), Construction & Building Technology, Critical Care Medicine, Crystallography, Dentistry (Oral Surgery & Medicine), Dermatology & Venereal Diseases, Developmental Biology, Ecology, Education (Scientific Disciplines), Electrochemistry, Emergency Medicine, Endocrinology & Metabolism, Energy & Fuels, Engineering (Aerospace), Engineering (Biomedical), Engineering (Chemical), Engineering (Civil), Engineering (Electrical & Electronic), Engineering (Environmental), Engineering (Geological), Engineering (Industrial), Engineering (Manufacturing), Engineering (Marine), Engineering (Mechanical), Engineering (Multidisciplinary), Engineering (Ocean), Engineering (Petroleum), Entomology, Environmental Sciences, Evolutionary Biology, Fisheries, Food Science & Technology, Forestry, Gastroenterology & Hepatology, Genetics & Heredity, Geochemistry & Geophysics, Geography (Physical), Geology, Geosciences (Multidisciplinary), Geriatrics & Gerontology, Health Care Sciences & Services, Hematology, History & Philosophy of Science, Horticulture, Imaging Science & Photographic Technology, Immunology, Infectious Diseases, Information Science & Library Science, Instruments & Instrumentation, Integrative & Complementary Medicine, Limnology, Marine & Freshwater Biology, Materials Science (Biomaterials), Materials Science (Ceramics), Materials Science (Characterization & Testing), Materials Science (Coatings & Films), Materials Science (Composites), Materials Science (Multidisciplinary), Materials Science (Paper & Wood), Materials Science (Textiles), Mathematics, Mathematics (Applied), Mathematics (Interdisciplinary Applications), Mechanics, Medical Ethics, Medical Informatics, Medical Laboratory Technology, Medicine (General & Internal), Medicine (Legal), Medicine (Research & Experimental), Metallurgy & Metallurgical Engineering, Meteorology & Atmospheric Sciences, Microbiology, Microscopy, Mineralogy, Mining & Mineral Processing, Multidisciplinary Sciences, Mycology, Neuroimaging, Neurosciences, Nuclear Science & Technology, Nursing, Nutrition & Dietetics, Obstetrics & Gynecology, Oceanography, Oncology, Operations Research & Management Science, Ophthalmology, Optics, Ornithology, Orthopedics, Otorhinolaryngology, Paleontology, Parasitology, Pathology, Pediatrics, Peripheral Vascular Disease, Pharmacology & Pharmacy, Physics (Applied), Physics (Atomic, Molecular & Chemical), Physics (Condensed Matter), Physics (Fluids & Plasmas), Physics (Mathematical), Physics (Multidisciplinary), Physics (Nuclear), Physics (Particles & Fields), Physiology, Plant Sciences, Polymer Science, Psychiatry, Psychology, Public & Environmental & Occupational Health, Radiology & Nuclear Medicine & Medical Imaging, Rehabilitation, Remote Sensing, Reproductive Biology, Respiratory System, Rheumatism, Robotics, Spectroscopy, Sport Sciences, Statistics & Probability, Substance Abuse, Surgery, Telecommunications, Thermodynamics, Toxicology, Transplantation, Transportation Science & Technology, Tropical Medicine, Urology & Nephrology, Veterinary Sciences, Virology, Water Resources, Zoology.
Social Sciences Citation Index covers more than 3,100 scholarly journals published worldwide, with coverage back to 1900. (Fewer titles are covered in the early decades.) It also picks up, selectively, social science articles appearing within approximately 3,500 science and technology journals. Major journals are indexed in all of these disciplines:
Anthropology, Area Studies, Business, Business (Finance), Communication, Criminology & Penology, Demography, Economics, Education & Educational Research, Education (Special), Environmental Studies, Ergonomics, Ethics, Ethnic Studies, Family Studies, Geography, Gerontology, Health Policy & Services, History, History & Philosophy of Science, History of Social Sciences, Hospitality (Leisure, Sport & Tourism), Industrial Relations & Labor, Information Science & Library Science, International Relations, Law, Linguistics, Management, Nursing, Planning & Development, Political Science, Psychiatry, Psychology, Psychology (Applied), Psychology (Biological), Psychology (Clinical), Psychology (Developmental), Psychology (Educational), Psychology (Experimental), Psychology (Mathematical), Psychology (Multidisciplinary), Psychology (Psychoanalysis), Psychology (Social), Public Administration, Public & Environmental & Occupational Health, Rehabilitation, Social Issues, Social Sciences (Biomedical), Social Sciences (Interdisciplinary), Social Sciences (Mathematical Methods), Social Work, Sociology, Substance Abuse, Transportation, Urban Studies, Women’s Studies.
Arts & Humanities Citation Index covers over 1,700 journals internationally back to 1975. It also picks up, selectively, humanities-related articles appearing in the science and social sciences fields. (For example, articles on foot and ankle injuries in ballet dancers, appearing in medical journals, are indexed here.) All of the following disciplines are covered:
Archaeology, Architecture, Art, Asian Studies, Classics, Dance, Film & Radio & Television, Folklore, History, History & Philosophy of Science, Humanities (Multidisciplinary), Language & Linguistics, Literary Reviews, Literary Theory & Criticism, Literature, Literature (African, Australian, Canadian), Literature (American), Literature (British Isles), Literature (German, Dutch, Scandinavian), Literature (Romance), Literature (Slavic), Medieval & Renaissance Studies, Music, Philosophy, Poetry, Religion, Theater.
Other components have recently been added to the family:
Book Citation Index (BCI): whereas the SCI, SCCI, and A&HCI cover scholarly journals, the BCI covers over 30,000 scholarly books, with 10,000 new titles to be added every year. Both “series” and “nonseries” books are covered provided that they include full footnote information. Two separate components are available: a Science edition covering Physics/Chemistry, Engineering/Computing/Technology, Clinical Medicine, Life Sciences, and Agriculture/Biology; and a Social Sciences & Humanities edition. The Science component extends back to 2005 and comprises 42 percent of the coverage; the Social Sciences & Humanities (also back to 2005) comprises 58 percent of the coverage. (Books, as opposed to journal articles, tend to be more important in the latter fields.) The company also offers a Conference Proceedings Citation Index (CPCI); it, too, comes in two components, Science and Social Sciences & Humanities. Together they cover over 110,000 proceedings in 256 categories since 1990, with about 12,000 new conferences added yearly. A new Data Citation Index identifies manipulable data sets in repositories around the world, and works making use of them.
The ideal subscription to the Web of Science database would combines all of these indexes, with coverage of the SCI back to 1900, the SSCI to 1900, and the A&HCI to 1975. Individual libraries, however, may opt for subscriptions to only one or two of the files rather than all, and they may select fewer years of retrospective coverage within any of them. In any event, the important point is this: Do not be misled by the word Science in the title; your library’s subscription may well include full coverage of the social sciences and humanities journals (and books/proceedings/datasets) as well. Indeed, your local library may list its subscriptions under the titles of the individual component databases rather than under the collective Web of Science designation. In any event, remember that if the collective Web title is used, the most important academic journals (and many recent books) in all fields are covered.
The overall value of these indexes is that they provide three different ways of doing subject searches in any subject area: by keywords, by footnote citations, and by related records (see Chapter 7 for the latter). Each of these search methods compensates for weaknesses in controlled vocabulary indexes; two of them (citation and related record) compensate for weaknesses in keyword searching, too—that is, they enable you find articles that lie in blind spots to the alternative indexing methods.
The citation search method is particularly valuable because, again, it circumvents vocabulary problems entirely.
An example is provided by the reader who was interested in the Norse colonization of America before Columbus. He had already found one good scholarly article discussing the evidence, but on running it through the SSCI he found a subsequent article by another scholar who disagreed with the conclusions of the first. And this was followed by a rebuttal by the original writer. The combination of perspectives developed by this dialogue brought up considerable information that did not appear in the first article.
Another example is provided by the researcher who wanted articles on “the economics of antiquities looting.” He found, in the SSCI component, one article from 1995 with those exact words in the title; he then discovered that this starting point had been cited by 17 subsequent articles from 1996 through 2008, and the citing articles have titles such as these:
These articles, while all playing in the same intellectual ballpark, nonetheless express the subject in a wide variety of keywords that could never have been thought up in advance. And although the keywords are apparently all over the map, they are nonetheless conceptually anchored by being linked to that initial relevant source: as disparate as they may be, they generally will not appear in irrelevant contexts. A citation search thus enables you to recognize directly relevant sources whose terminology you would not be able to think up on your own and which would also be missed by any relevance ranking algorithm working only with the words you’ve actually typed.
Within the Web of Science there are two different ways to do citation searching. First, you can start by doing a regular keyword search to find articles indexed within any of the 13,500 journals (and other sources) covered by the database; any retrieved item will contain a note telling you if it has been cited by subsequent sources and will provide a live link that will bring up a list of all of them.
Second, you can use the “Cited Reference Search” tab on the Web of Science search screen. In order to find this link, however, you must first click on the downward arrow next to the default “Basis Search” option. “Cited Reference Search” will then appear in the drop-down menu. If you begin here, you can look for any source at all—even if it is not an article that is keyword indexed within the 13,500 journals or the books or proceedings. It could be an article appearing in any of the tens of thousand of other journals outside the Web of Science’s range of keyword indexing, or it could be something other than a journal article to begin with: a book or a doctoral dissertation or any other source published anywhere, at any time. “Cited Reference Search” will then tell you if that source—wherever it comes from and whenever published—has been cited by any article within any of the 13,500 journals, books, or conference proceedings indexed in Web of Science.
There are, of course, limitations to the technique of citation searching: you must already have a good source to start with; further, there is no guarantee that all of the subsequent relevant literature, or all of the best sources, will cite your starting point source. It is quite possible that good works exist that are not linked by footnote connections. Sometimes, too, a good source will be cited by another in a context that is not conceptually relevant to your interest. Again, there are always trade-offs you need to keep in mind. Citation searching solves many research problems that are otherwise intractable, but it cannot solve all of them (any more than controlled vocabulary or keyword searching can solve all problems). In many situations, however, it does produce results that are strikingly better than the alternative techniques provide.
The importance of cross-disciplinary searching has already been discussed in Chapter 4 but is worth returning to in the present context because of the remarkable range of disciplines covered simultaneously by the Web of Science databases. The extent of that coverage is indicated in the descriptions, above, of its SCI, SSCI, A&HCI, BCI, and CPCI components.
Even within the Science Citation Index itself, apart from the others, the range of cross-disciplinary coverage is amazing. Eugene Garfield, the creator of these Citation databases, mentions a spectacular example in his book Citation Indexing: Its Theory and Application in Science Technology, and Humanities (John Wiley & Sons, 1979, p. 4):
From 1961 to 1969 a citation for one of the classic papers published by Albert Einstein in Annallen der Physik in 1906 is linked [by the SCI] to papers in the Journal of Dairy Sciences, Journal of the Chemical Society, Journal of Polymer Science, Journal of Pharmacy and Pharmacology, Comparative Biochemistry and Physiology, Journal of General Physiology, International Journal of Engineering Science, Journal of Materials, Journal of the Water Pollution Control Federation, American Ceramic Society Bulletin, Journal of the Acoustical Society of America, Chemical Engineering Science, Industrial and Engineering Chemistry Process Design and Development, Journal of Colloid and Interface Science, Journal of Fluid Mechanics, Journal of Lubrication Technology, Journal of Molecular Biology, Journal of Food Science, Journal of Biological Chemistry, Journal of Sedimentary Petrology, Review of Scientific Instruments, and the Journal of the Electrochemical Society.
Students of literature or classics, particularly, should keep the Arts & Humanities Citation Index in mind as something to be used routinely as a supplement to the MLA International Bibliography, the Annual Bibliography of English Language and Literature, and L’Année Philologique. For example, I once helped a professor who was interested in the ancient explorer Pytheas. A Web of Science search on this topic produces articles from the journals Arctic, Mariner’s Mirror, Prairie Schooner, Library Journal, and the book series History of Mechanism and Marine Science—none of which are covered in the standard index for classical studies, L’Année Philologique.
Similarly, a musicologist compiling a massive bibliography on the Russian composer Alexander Scriabin found, via Web of Science, an article on “The Evolution of One-Handed Piano Compositions” that references him in the Journal of Hand Surgery. Obviously this publication is not indexed in any of the conventional music or performing arts databases. Likewise, a philosopher interested in “Aristotle’s conception of time” found an article on “Changes in Concepts of Time from Aristotle to Einstein” in Astrophysics and Space Science, a journal not indexed by the major philosophy database, The Philosopher’s Index.
A particularly useful extension of citation searching is to “cycle” sources—that is, once you have found a first set of articles citing your original source, you can then look to see who cited them. This will give you a second set; you can then see who cited this group, which will provide a third set, and so on. By pursuing this process as far as is productive, you can sometimes generate a great deal of information on even very obscure topics.
While the Web of Science is useful in enabling you to follow the development of a debate or the progress of a scholarly discussion, it is also very useful when the various book review databases fail, for there is still a chance that the book you’re interested in may have been commented on, or referred to critically or favorably, in a journal article even if it has not been formally reviewed. The Web of Science also provides the best way to find a “review” (or a critical response to) a journal article, as these are not covered by book review indexes. It is especially good for giving a new lease on life to the material you locate through old bibliographies—if the latter refer you to somewhat dated articles, you can find out if someone has used them as background sources for a new look at the subject. It is particularly worthwhile to see if anyone has cited old state-of-the-art review articles (see Chapter 8).
These databases often plays a part, too, in academic circles on questions of tenure or promotion, for departments wish to know not only whether a candidate has published, but also if he or she has been cited by other scholars in the field, especially in the most important journals. (Academics who wish to document how frequently their own works have been cited, however, should not confine their searches to Web of Science alone because now there are many other databases that provide citation searching.)
Several other features of the Web of Science are worth noting:
Thomson Reuters also offers a separate subscription to a related database called Journal Citation Reports (JCR). This provides statistical information showing the relative importance and ranking of individual journals within their disciplinary fields. Data are also given regarding a journal’s “Impact Factor” (measuring how frequently an average article in the journal is cited in a given year) and its “Immediacy Index” (measuring how quickly an average article is cited). Unfortunately, JCR covers only the Science and Social Sciences journals within the overall Web of Science universe; it does not provide any data for the Arts & Humanities titles. (Institutions may also subscribe to the publisher’s InCites service, which provides reports on departmental [and other] rankings and comparisons to peer institutions; InCites uses the JCR data, but the company does all the analytical work for you.)
Although the editors do a very good job of indexing the most important journals in all subject areas, no single index can be relied on to cover all relevant individual articles. Quality papers have a way of showing up rather far afield from where they might be expected to appear—which means that you will always have to use multiple databases or bibliographies for thorough searching. Remember, too, that none of these Citation databases provide access through controlled subject headings or descriptors. If you search the same journals through other databases that index them using controlled terms (e.g., Historical Abstracts, PsycINFO, Academic Search Complete, etc.), you will be able to see different results within them.
Thomson Reuters also publishes a more specialized citation database: Biosis Citation Index covers 6,000 titles in biomedical fields back to 1926; it offers enhanced search features (e.g., indexing by Enzyme Commission numbers) not found in the regular SCI database.
Citation search capabilities are now appearing in many databases beyond those in the Thomson Reuters family. Some of the more prominent databases offering this search method are listed here.
Scopus (from Elsevier) is another subscription database; a full description of it is freely available at www.info.sciverse.com/scopus/scopus-in-detail/facts/. Essentially, it is the largest citation index available, covering about 22,000 scholarly journals worldwide in “scientific, technical, medical, and social sciences fields and arts and humanities,” as well as more than 370 book series. Its criterion of selection is whether a source is peer-reviewed, not whether the source is frequently cited by others. About 60 percent of its coverage comes after 1995; the 40 percent of earlier sources date back as far as 1823. Although the bulk of its indexing lies in scientific fields, it indexes many more social sciences and humanities journals that does Web of Science. It, too, allows keyword searching, citation searching, and related record searching; it also enables researchers to zero in immediately on literature review articles (see Chapter 8).
In each of these databases look for the search tab “Cited References” along the top bar of the search page. (You won’t notice it at all if you’re not deliberately looking for it.)
Other databases will undoubtedly be added to this list in the future. Note that if you do a federated search of several EBSCO databases simultaneously, the “Cited References” search option will disappear. That is one reason it is usually best to search each of the databases you want separately, rather than in a merged pool.
The EBSCO databases that offer citation indexing—and it’s not all of them—also provide another way to get at articles that cite your starting-point source: if you initially do a keyword or subject search and find any relevant articles, the records for any of them may also provide a link indicating “Time Cited in This Database”—clicking on this will provide you with subsequent articles that cite these initial sources. In other words, you can start the process via a keyword (or descriptor) search, and then extend your results via citation searching.
The citation-search feature in these databases is, unfortunately, extremely well hidden. You must first select an individual database (not the default merged pool of all of them), then select “Advanced” search, then use the drop-down menu next to any of the search boxes, to find the search option for “References – REF” in order to do citation searching. As of this writing, these databases offer this search feature:
Again, the “References – REF” search option (in the drop-down menus) will not appear at all if you do a federated search of multiple databases simultaneously.
Sage Journals (Sage) offers nearly 700 journals, with “References” as a search option in the drop-down menus of its “Advanced” search screen.
Academics, take note: if you are looking to see how often your have been cited yourself for promotion or tenure review purposes, using the citation search features of these other databases can turn up many additional hits that are not recorded in Web of Science.
Still other databases from other vendors are likely to offer citation searching in the future; the important point is to be aware of the possibility of doing this kind of search, and to actively look for it on any “Advanced” search screen you happen to be working with. (Always choose the database’s “Advanced” search screen to begin with, and take a minute to familiarize yourself with its search tabs at the top of the screen and its drop-down menus next to the search boxes. Very few researchers do this, but it can make an enormous improvement in the quality of retrievals.)
Note, further, that many databases offering full texts of academic journals essentially allow a form of citation searching simply by the fact that they make the keywords of the footnotes just as searchable as words within the articles; so, even if the files do not formally index the footnotes as a separate document type (indicated in a drop-down menu), you can still search for the titles of articles or books as keyword phrases (i.e., within quotation marks), and you may well get “hits” of these titles appearing within the full-text digitized footnotes or bibliographies.
Google Scholar, which includes texts of academic and other journals, is essentially a keyword searchable file, with the usual term weighting (or relevance ranking) found elsewhere in Google, but Scholar provides and additional “wrinkle” in that, like Web of Science and several EBSCO databases, it will tell you if any given hit that comes up has been “Cited by” any other articles within the database. The only problem here is that you never know what you’re getting in Scholar—or, just as important, what you are not getting. The company will not reveal which journals are indexed, nor which issues are being searched, or how much of a backfile is included.
Most of the databases discussed so far in this chapter will tell you if any given source has been cited in the footnotes of a subsequent journal article. Many researchers, of course, wish to know in addition if their given source has been cited by any books. The best way to look for this kind of linkage (apart from Book Citation Index) as of this writing is through either Google Books, Amazon’s Look Inside the Book feature, the Hathi Trust Digital Library (www.hathitrust.org), or the Internet Archive (https://archive.org). These services make full texts of books keyword-searchable; again, that makes their footnotes searchable as well. In using Google Books or Hathi Trust, be sure to use quotation marks around any title (or other) phrases that you wish to look for.
The overall point of this chapter is that citation searching provides a useful way around the persistent problem of determining the best search terms for your topic. Given the weaknesses of keyword searching, you want to be aware of the other methods of getting at your topic that will bring to your attention relevant works whose keywords you cannot specify in advance. The traditional ways of circumventing this difficulty lie in controlled vocabulary searching and in browsing classified bookstacks (both of which enable you to recognize relevant terms within carefully defined conceptual categories). Citation searching provides yet another way around the problem. Still other ways will be discussed in the next chapters.