Every year upwards of 9 million scientists and scholars publish their findings in academic journals, producing papers that, according to some estimates, likely number in excess of 2 million.
With such prodigious output, the task of qualifying the value of each piece of work is challenging. Nevertheless, the research community, publishers, academic administrators and others seek such clarification, beyond means such as who commands the highest salaries, biggest laboratories or office shelves with the most awards.
One strategy, steering clear of the marginal factors noted above, is to concentrate on the research papers themselves – specifically, the extent to which they have assisted, inspired or challenged other researchers. Papers meeting this standard earn a clear distinction when other authors explicitly footnote, or cite, the reports in their subsequent work. A paper that other authors have frequently cited has quantifiably proved itself to be significant.
Extending this logic provides a clear avenue to seek out authors who have consistently produced papers which have, in turn, won peer approval in the form of high citation counts.
This approach is embodied in the Thomson Reuters Highly Cited Researchers, a searchable compendium covering the main areas of science and the social sciences, representing the researchers who, in their respective fields, have contributed markedly high numbers of top-cited papers.
The Top 1%
Compiled annually, the Highly Cited Researchers listing derives from Essential Science Indicators (ESI), a component of the Web of Science. Among its assorted features and metrics, ESI tracks papers published in the last decade that rank in the top 1% most cited for their respective years of publication in each of the main subject fields. These reports, officially designated as “Highly Cited Papers,” numbered more than 120,000 in a recent analysis covering the years 2003 to 2013.
From this cohort of Highly Cited Papers, Thomson Reuters analysts identified author names listed on multiple reports within each ESI field. (Each paper is assigned to only one field, depending on the journal in which it appeared. Any paper published in a multidisciplinary journal, such as Science or Nature, is assigned based on algorithmic analysis of the literature predominantly cited by the paper, as well as of the journals which subsequently cited the report. For example, a Science paper that mostly cites immunology reports, and is in turn cited by papers published in immunology journals, would be assigned to the field of Immunology.)
Analysts solve for cases of identical researcher names by examining individual papers and their listings of authors and institutions. When necessary, authors’ Web pages and curricula vitae are also consulted in order to verify assignment of papers to the proper person.
Once the papers have been accurately attributed, the authors are listed within each ESI field, according to the number of Highly Cited Papers to their credit. In all, the current listing of Highly Cited Researchers features more than 3,100 names.
The specialty areas covered by ESI differ drastically in size. That is, some fields are characterized by greater numbers of journals, in which larger populations of authors publish more papers, and therefore greater quantities of Highly Cited Papers. For example, the field of Clinical Medicine is the largest in ESI, accounting for about 12% of the database’s total content. Economics & Business, meanwhile, contributes just over 2%.
The relative size of each ESI field, in terms of the overall number of Highly Cited Papers, was factored into the thresholds that determined how many authors to feature in each field. Varying thresholds are also included in determining how many Highly Cited Papers were required to qualify a given author.
Figure 1 reflects the variance in the size and the corresponding yield of Highly Cited Researchers for the top 10 of the 21 ESI fields, showing the number of authors within each area. Clinical Medicine, as noted above, is unmistakably predominant.
Of the 3,126 Highly Cited Researchers in the 2015 listings, 1,563 represent US-based institutions – precisely 50%. The United Kingdom followed at some distance, with Germany and China also registering strongly. Figure 2 represents a breakdown by nation.
Some institutions proved to be notably prolific in hosting Highly Cited Researchers, as Table 1 indicates.*
Again, size is a factor, as several of the entities represent large university systems or national research agencies with many component facilities. The University of California, which boasts the greatest number of names with 165, is an example, as are the US National Institutes of Health and the Chinese Academy of Sciences.
Still, some smaller players emerged, such as Washington University in St. Louis, and the Broad Institute of MIT and Harvard in Cambridge, Massachusetts. Thanks to their researchers’ contribution to several highly cited genomics papers, both organizations can claim upwards of two-dozen Highly Cited Researchers.
Tabulating the most highly cited papers is just one of several possible citation-based measurements for assessing a researcher’s impact. Another approach is to gauge “relative impact” by comparing a citations-per-paper tally against a field-wide baseline. No single approach is ideally comprehensive in scope or outcome, and any scheme will likely exclude accomplished, deserving researchers who do not happen to meet the criteria at hand.
The measure used for identifying Highly Cited Researchers, however, has the advantage of reflecting recent contributions that may come from early- or mid-career researchers, rather than relying on an overall citation count, a measure that tends to favor authors whose work has had many years in which to accumulate citations.
Undeniably, Highly Cited Researchers have demonstrated that their work is central to current, ongoing research across the range of scholarly and scientific advancement and that they are the ones to watch.
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