The data used in the analysis and selection of the new highly cited researchers came from Essential Science Indicators, 2002-2012, which then included 113,092 Highly Cited Papers. Each of these papers ranked in the top 1% by total citations according to their ESI field assignment and year of publication (as stated above, more correctly, year processed for the Web of Science). For more information on the identification of Highly Cited Papers in ESI, see the ESI help file at Essential Science Indicators
ESI surveys the SCI-E and SSCI components of the Web of Science, meaning journal articles in the sciences and social sciences. The analysis is further limited to items indexed as articles or reviews only, and does not include letters to the editor, correction notices, and other marginalia.
In ESI, all papers, including Highly Cited Papers, are assigned to one of 22 broad fields (the 22nd is Multidisciplinary, on which see below). Each journal in ESI is assigned to only one field and papers appearing in that title are similarly assigned. In the case of multidisciplinary journals such as Science, Nature, Proceedings of the National Academy of Sciences of the USA, and others, however, a special analysis is undertaken. Each article in such publications is individually reviewed, including an examination of the journals cited in its references as well as the journals from which citations to it derive. The ‘weight’ of these cited and citing relationships helps to assign papers to a specific ESI field. For more information about this reclassification process, see our article at Classification of Papers in Multidisciplinary Journal. In fact, this procedure includes not only those journals that are widely recognized as multidisciplinary, but others, too, that within Clinical Medicine, publish papers across a wide number of specialty areas (these include: Annals of Internal Medicine, British Medical Journal, Journal of the American Medical Society, The Lancet, New England Journal of Medicine, Journal of Clinical Investigation, Cell, Journal of Experimental Medicine, and Nature Medicine). Some few papers (> 5% in the case of Science, Nature, and PNAS) are unable to be assigned to a specific field and remain in the Multidisciplinary category in ESI. As such, Multidisciplinary in ESI should be recognized as a grouping of ‘leftovers’ and, therefore, not very useful for performance analysis.
A ranking of author names in each ESI category by number of Highly Cited Papers produced during 2002-2012 was the first step in identification and selection of our new list of highly cited researchers. We used algorithmic analysis to help distinguish between individuals with the same name or name form (surname and initials). In instances where any ambiguity remained, manual inspection was needed. This entailed searching for papers by author surname and one or multiple initials, ordering them chronologically, visually inspecting each (noting journal of publication, research topic or theme, institutional addresses, co-authorships, and other attributes), and deciding which ones could be attributed to a specific individual. As noted in the FAQ section, we examined original papers, if necessary, as well the websites of researchers themselves and their curricula vitae. This was often required if a researcher changed institutional affiliations several times during the period surveyed.
Once the data on Highly Cited Papers within an ESI field were verified and assigned to specific individuals, the authors in the field were ranked by number of Highly Cited Papers. To determine how many researchers to select for inclusion in the new list, we considered the size of each ESI field in terms of number of authors (as a proxy for population) represented on the Highly Cited Papers for the field. The ESI fields are of very different sizes, the result of the definition used for the field which includes the number of journals assigned to that field. Clinical Medicine, for example, makes up some 19% of the content of ESI while Economics and Business, Microbiology, and Space Science (Astronomy and Astrophysics) account for 1.7%, 1.4%, and 1.1%, respectively. For each ESI field, author names (before use of the PDE algorithm and therefore not disambiguated) were counted, and then the square route of that number was calculated. That number was used to decide approximately how many researchers to include in each ESI field. From the list of authors in a field ranked by number of Highly Cited Papers, the number of papers at the rank represented by the square root score determined the threshold number of Highly Cited Papers required for inclusion. If an author had one fewer highly cited paper than this threshold, but whose citations to their Highly Cited Papers were sufficient to rank them in the top 50% by citations among those with Highly Cited Papers at or above the threshold, these individuals were also selected. Finally, citations to an individual’s Highly Cited Papers had to meet or exceed the threshold for total citations used in the 2002-2012 version of ESI for including a researcher in the top 1% (highly cited list) for an ESI field.
The methodology described above was applied to all ESI fields with the exception of Physics. The relative large number of Highly Cited Papers in Physics dealing with high-energy experiments typically carried hundreds of author names. Using the whole counting method produced a list of high-energy physicists only and excluded those working in other subfields. For example, the number of Highly Cited Papers required for inclusion in Physics, using the standard methodology, turned out to be a remarkable 63. So, as an expedient, it was decided to eliminate from consideration any paper with more than 30 institutional addresses. This removed 436 out of 10,373 Highly Cited Papers in physics and the problem of overweighting to high-energy physics. An analysis without these papers produced a list in which the threshold for number of Highly Cited Papers was 14. It also produced a ranking in which the 2010 Nobel Prize winner in Physics Andre Geim of the University of Manchester appeared first, with 40 Highly Cited Papers. Fields of physics other than high-energy alone now appear as represented by the scientists selected.
The final new list contains some 3,200 highly cited researchers in 21 fields of the sciences and social sciences.