Much of this book rests on the use of “citations” data. Some readers may be unfamiliar with such data. Citations are references to other people's work. In journals and books, scholarly knowledge is developed publication by publication. Older knowledge is acknowledged in current work through the writer's bibliography and references. If Dr. Ζ has 718 citations, that means that Dr. Z's research papers and books have been mentioned by others (that is, in others' reference lists) 718 times. Organizations like the Institute for Scientific Information (ISI, now owned by Thomson) keep track of such totals.
All the citation information used in this study comes from the Institute of Scientific Information (ISI) Web of Knowledge, the online database comprising the Science Citation Index, Social Science Citation Index, and the Arts and Humanities Citation Index. The other more recent place available for counting citations is through Google Scholar, which was not a reliable source when I started this project in 2004. Even today Google Scholar picks up citations from unpublished papers as well as published ones. ISI allows citations from published peer reviewed work only to be counted.
It is important when using citations as any kind of measure to recognize the huge differences between disciplines. For example, a highly cited social scientist might have a lifetime citation score of between 1,000 and 2,000, whereas a molecular biologist could have a score over 15,000. Bibliometric indicators have been used more consistently across the sciences, particularly in the natural and life sciences, though less so in engineering and the behavioral sciences. These disciplines publish more journal articles and have a higher prevalence of coauthorship.
The social sciences are patchier. For example, economics relies heavily on journal articles, although, unlike the science publications that tend to publish quickly, in the subject of economics it can be over two years from submission to publication. It is less common in the arts and humanities to write articles for journals: these disciplines tend more toward the publishing of books. Cronin and colleagues found that in the discipline of sociology two fairly distinct groups of highly cited academics coexisted: those highly cited through their journal articles and those through their monographs.1 This should not present a major problem
1 Cronin etal. (1997).