The rules for the 2025 version of the influential Highly Cited Scientists list exclude scientists whose co-authors have engaged in practices such as a tendency to cite their own papers. Credit: Getty
The creators of an influential list of highly cited researchers have shaken up their methodology this year, taking a swipe at scientists who associate with those linked to possible ethical breaches. The new rules have allowed the field of mathematics to return to the list, after being excluded for the past two years owing to concerns over suspicious citation patterns.
The Highly Cited Researchers (HCR) list is produced by the multinational data-analytics company Clarivate, which also owns the Web of Science database. The list aims to recognize contemporary researchers with “significant and broad influence”, who are among the authors of papers that are in the top 1% in their field by number of citations. The programme recognizes thousands of individuals each year across 21 natural- and social-science fields and factors into influential rankings of universities.
Thousands of highly cited scientists have at least one retraction
This year, the list was compiled with a new step: exclusion of any papers with an author who had been knocked off the previous year’s HCR list owing to research-integrity issues. This means that anyone who routinely co-authored papers with someone who’d been excluded in the previous year was less likely to be acknowledged than before the change.
“It’s quite a good idea. It’s a big cleaning,” says Lauranne Chaignon, a bibliometrician at PSL University in Paris, who has studied the HCR list1. There is, she adds, a small chance of removing a deserving scientist.
This year’s list, announced today, recognizes 6,868 people.
Gaming the system
Starting around 2016, HCR organizers noticed a rise in suspicious activity in the data used to compile the list, says David Pendlebury, head of research analysis at Clarivate’s Institute for Scientific Information (ISI). The issue became most pronounced in maths: a few people were publishing large numbers of papers, especially in the field of fractional differential equations. These authors frequently cited each other, causing others to fall off the HCR list. “A lot of these people were not known to us, and they were from institutions sometimes we’d never heard of,” says Pendlebury. “The world-famous mathematicians that we originally were seeing were disappearing.”
Maths is particularly vulnerable to gaming because its metrics are small: mathematicians tend to publish fewer papers with fewer co-authors and citations than do academics in other fields2. “Just a few more citations into the system is quite disruptive,” says Pendlebury. As a result, Clarivate chose to omit the field entirely from the 2023 and 2024 lists.
Simple fix
The process of constructing the HCR list starts with a ‘long list’ of about 200,000 papers and reviews that are in the top 1% in their field by citation count. The ISI team then whittles this down by removing retracted papers and those with more than 30 authors (on which it’s hard to determine individual contributions), for example.
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