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Highly Cited Researchers
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2019 RecipientsMethodologyFAQs

Overview

  • The Highly Cited Researchers list from the Web of Science Group identifies scientists and social scientists who have demonstrated significant influence through publication of multiple papers, highly cited by their peers, during the last decade.
  • Researchers are selected for their exceptional performance in one or more of 21 fields (those used in the Web of Science Group's Essential Science Indicators , or ESI) or across several fields.
  • All Highly Cited Researcher records are reviewed. Factors such as retractions, misconduct, and extreme self-citation—all of which would detract from true community-wide research influence—may lead to an author being excluded or suppressed from the list. Approximately 6,200 researchers are named Highly Cited Researchers in 2019—some 3,700 in specific fields and about 2,500 for cross-field performance. This is the second year that researchers with cross-field impact are identified. The recognition of researchers with substantial influence in several fields keeps the Highly Cited Researcher list contemporary and relevant.
  • The number of researchers selected in each field is based on the square root of the population of authors listed on the field’s highly cited papers. The number of those with cross-field influence is determined by finding those who have influence equivalent to those identified in the 21 fields.
  • For the 2019 Highly Cited Researchers analysis, the papers surveyed were the most recent papers available to us—those published and cited during 2008-2018 and which then ranked in the top 1% by citations for their ESI field and year (the definition of a highly cited paper).
  • The threshold number of highly cited papers for selection differs by field, with Clinical Medicine requiring the most and Economics & Business the least.
  • A second criterion for selection is a citation count to highly cited papers that ranks a researcher in the top 1% by citations in an ESI field for the period surveyed.
  • To identify researchers with cross-field influence, highly cited paper and citation counts are normalized through fractionating according to the thresholds required for each field (thus, each Clinical Medicine paper has a smaller unit fraction than one in Economics & Business). Citation counts are fractionated in a similar manner. If the sum of the publication counts and the sum of the citation counts for a researcher equals 1.0 or more, the individual exhibits influence equivalent to a researcher selected in one or more ESI defined fields and is therefore selected as a Highly Cited Researcher for exceptional cross-field performance.
  • There is no unique or universally agreed concept of what constitutes exceptional research performance and elite status in the sciences and social sciences. Consequently, no quantitative indicators will point to a list that satisfies all expectations or requirements. Moreover, a different basis or formula for selection could generate a different—though likely overlapping—list of names. Thus, the absence of a name on our list cannot be interpreted as inferior performance or stature in comparison to those selected this year.
  • Although this list is updated and refreshed each year, a Highly Cited Researcher is always a Highly Cited Researcher—whether their name was included in 2013 or 2019.
  • Please read the full methodology with care to understand both the meaning and the inevitable limitations of our analytical approach.
Click here for a detailed description of the purpose and methodology of Highly Cited Researchers.
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Highly Cited Researchers from the Web of Science Group is an annual list recognizing influential researchers in the sciences and social sciences from around the world. The 2019 list contains about 3,700 Highly Cited Researchers in 21 fields of the sciences and social sciences and about 2,500 Highly Cited Researchers identified as having exceptional performance across several fields. The list focuses on contemporary research achievement: only highly cited papers in science and social sciences journals indexed in the Web of Science Core Collection during the 11-year period 2008-2018 were surveyed. Highly cited papers are defined as those that rank in the top 1% by citations for field and publication year.

The data derive from Essential Science Indicators (ESI), a component of InCites. The fields are also those employed in ESI – 21 broad fields defined by sets of journals and exceptionally, in the case of multidisciplinary journals such as Nature and Science, by a paper-by-paper assignment to a field based on an analysis of the cited references in the papers. This percentile-based selection method removes the citation advantage of older papers relative to recently published ones, since papers are weighed against others in the same annual cohort.

Researchers who, within an ESI-defined field, publish highly cited papers are judged to be influential, so the production of multiple top 1% papers is interpreted as a mark of exceptional impact. Relatively younger researchers are more likely to emerge in such an analysis than in one dependent on total citations over many years. To be able to recognize early and mid-career as well as senior researchers is one of the goals in generating the list of Highly Cited Researchers. The determination of how many researchers to include in the list for each field is based on the population of each field, as represented by the number of disambiguated author names on all highly cited papers in that field, 2008-2018. The ESI fields vary greatly in size, with Clinical Medicine being the largest and Economics & Business being the smallest in terms of researchers. The square root of the number of authors in each field indicated how many individuals should be selected.

Authors with the greatest number of highly cited papers in an ESI field at the threshold for inclusion and above are putative selectees. However, another criterion for selection is that the researcher must have enough citations to his or her highly cited papers to rank among all authors in the top 1% by total citations in the ESI field in which that person is considered. All who published highly cited papers at the threshold level and with citations in the field at the level of top 1% are admitted to the list, even if the final list then exceeds the number given by the square root calculation.

In addition, and as concession to the somewhat arbitrary cut-off, any researcher with one fewer highly cited paper than the threshold number is also admitted to the list if total citations to his or her highly cited papers ranks that individual in the top 50% by total citations of those at the threshold level or higher. The justification for this adjustment is that it seems to work well in identifying influential researchers, in the judgment of the Web of Science Group's citation analysts.

Of course, there are many highly accomplished and influential researchers who are not recognized by the method described above and whose names do not appear in the 2019 list. This outcome would hold no matter what specific method were chosen for selection. Each measure or set of indicators, whether total citations, h-index, relative citation impact, mean percentile score, etc., accentuates different types of performance and achievement. Here we arrive at what many expect from such lists but what is unobtainable: that there is some optimal or ultimate method of measuring performance. The only reasonable approach to interpreting a list of top researchers such as ours is to fully understand the method behind the data and results, and why the method is used. With that knowledge, in the end, the results may be judged by users as relevant or irrelevant to their needs or interests.

Details of Methodology

The data used in the analysis and selection of Highly Cited Researchers derives from Essential Science Indicators (ESI), 2008-2018, which then included approximately 150,000 highly cited papers. Each of these papers ranked in the top 1% by total citations according to its ESI field assignment and year of publication. For more information on the identification of highly cited papers in Essential Science Indicators, see the ESI help file at Essential Science Indicators.

Essential Science Indicators

Essential Science Indicators surveys the Science Citation Index Expanded and Social Sciences Citation Index 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.

Classification

In Essential Science Indicators, 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 Essential Science Indicators 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, 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. The paper is then reclassified to the most frequently occurring field represented by the article’s cited references.

Getting to the Final List

For each ESI field, author names are disambiguated through advanced clustering methods and the number of clusters is counted, each cluster representing a unique individual. Based on the number of clusters (individuals) for each field, the square root of that number is calculated. That number is 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 determines the threshold number of highly cited papers required for inclusion.

In addition, citations to an individual’s highly cited papers must meet the threshold for total citations used in the 2006-2016 version of ESI for including a researcher in the top 1% (highly cited list) for an ESI field.

If an author has one fewer highly cited paper than this threshold, but citations to their highly cited papers ranks them in the top 50% by citations among those with highly cited papers at or above the threshold, these individuals are also selected.

Example:

Click here to open the example in a new tab.
ESI FieldFirst NameLast NameHCPsCitation to HCPsField Paper ThresholdField Citation ThresholdField Citation Threshold if One Fewer Paper than Threshold NumberStatus
Field 9MaryPandit1728381111122920Selected
Field 9WilliamClever1036771111122920Selected
Field 9JudithSage1013381111122920Not Selected

 

Adding Researchers with Cross-Field Impact

A criticism of past Highly Cited Researchers lists was that the methodology systematically neglected to identify and in effect penalized researchers with cross-field influence: a researcher might contribute multiple highly cited papers in several different fields but would not register enough highly cited papers in any one field for selection. The criticism was valid and welcome. To find individuals with impact equivalent to those we select in a single field, we normalize the highly cited paper counts across fields, so that a paper in Clinical Medicine has the same ‘weight’ as one in Economics & Business. To do this we fractionate the count for each highly cited paper according to the threshold number used in each field. The fraction for a paper is larger in Economics & Business than in Medicine. If, after collecting all the highly cited papers of an author in all fields we find that the sum of the fractionated paper counts is 1 or more, this demonstrates that the individual has as much influence as those chosen in a single field. A similar procedure is employed for the citation counts, the second criteria for selection.

Example:

Click here to open the example in a new tab.
ESI FieldFirst NameLast NameHCPsCitation to HCPsField Citation ThresholdField Paper ThresholdField Paper ScoreField Citation ScoreCross-Field Paper ScoreCross-field Citation Score
Field 3JosephSavant1981857220.0450.0531.6705.666
Field 6JosephSavant7293794680.8753.1051.6705.666
Field 14JosephSavant366367660.50.9811.6705.666
Field 16JosephSavant433972223160.251.5281.6705.666

 

The fictional researcher Joseph Savant published 15 highly cited papers in four ESI fields during the period 2008-2018. Seven papers in Field 6, with a threshold number of eight for selection, earned Savant a credit of .875 (or 7/8ths). Three papers in Field 14, with a threshold number of six for selection, were worth .5. The sum of the fractional paper counts in each field yielded a total Cross-Field paper score of 1.67. A score of 1 or more indicates that the individual achieved impact equivalent to a researcher chosen in a specific ESI field. The second criterion for selection as a Highly Cited Researcher is enough citations to rank in the top 1% by citations for a field. Again, citations in different fields were fractionated in a similar manner to the treatment of papers. In the example above, Professor Savant earned more than five times the number of citations needed for selection as an influential cross-field researcher.

Exceptions

In past years, the methodology described above was applied to all ESI fields except for Physics and Space Sciences (Astronomy and Astrophysics). In these two fields, any paper with more than 30 institutional addresses was removed for our analysis. Many highly cited papers in Physics and in Space Science dealing with high-energy experiments and large-team space missions, respectively, typically carry hundreds of author names, and using the whole counting method for author credit, without removing such papers, produced a list of high-energy physicists only or those participating in large-team space missions only and excluded those working in other subfields. In the past few years, we have noted an increase in massively multi-authored paper and not only in these two fields. In the 2008-2018 data, we determined that fully 5% of the highly cited papers in Molecular Biology and Genetics exhibited more than 30 institutional addresses and were the contribution of many authors. To award credit to a single author among hundreds listed on a paper strains reason, so this year any highly cited paper, in any of the 21 fields, was eliminated from our analysis.

Exclusions

Finally, we exclude retracted articles in our analysis of highly cited papers. Also, researchers found to have committed scientific misconduct in formal proceedings conducted by a researcher’s institution, a government agency, a funder or a publisher are excluded from our list of Highly Cited Researchers.

Another change in our methodology this year was the exclusion of authors whose collection of highly cited papers revealed unusually high levels of self-citation. For each ESI field, a distribution of self-citation was obtained, and extreme outliers (a very small fraction) were identified and evaluated.

Executive Summary

Experts from the Institute for Scientific Information provide exclusive insight into the list of Highly Cited Researchers 2019, including the methodology, country, and institutional breakdowns, and much more.