*Update: The original story below generated so much attention on social media that we followed up with another article that noted reactions, a fuller explanation of the story and why certain people were not included, and an expanded list of most followed practicing research scientists on Twitter.

Genomicist Neil Hall sparked an online tempest this summer by proposing a “Kardashian Index,” or K-index—a comparison of a scientist’s number of Twitter followers with their citations. Scientists with a high score on the index, named after the reality TV star Kim Kardashian, one of the most popular celebrities on the social media platform, should “get off Twitter” and write more papers, suggested Hall, who works at the University of Liverpool in the United Kingdom.

Though Hall says he meant his K-index lightheartedly, his article in Genome Biology sparked a Twitter storm of criticism. So just who are the Kardashians of science, and is Hall’s criticism justified? Hall tactfully declined to provide a K-index for anyone specific, but Science was curious about the names and the numbers. We have compiled a list of the 50 most followed scientists on the social media platform and their academic citation counts—and calculated their K-index by drawing on citation data from Google Scholar (A fuller explanation of how we compiled the list is below, at the end of the full story).

The top three science stars of Twitter:

(Based on followers)

1. Neil deGrasse Tyson, Astrophysicist

2,400,000 followers @neiltyson

Citations: 151 K-index: 11129

Total number of tweets: 3,962

Hayden Planetarium, United States

2. Brian Cox, Physicist

1,440,000 followers @ProfBrianCox

Citations: 33,301 K-index: 1188

Total number of tweets: 10,300

University of Manchester, United Kingdom

3. Richard Dawkins, Biologist

1,020,000 followers @RichardDawkins

Citations: 49,631 K-index: 740

Total number of tweets: 19,000

University of Oxford, United Kingdom

Rather than identifying “Science Kardashians”—those who are, as Hall put it, “famous for being famous”—the top 50 list reveals that a majority of the science Twitter stars spend much, if not all, of their time on science communication. For them, Twitter popularity can amplify their efforts in public outreach. A case in point is Neil deGrasse Tyson, director of the Hayden Planetarium in New York City and host of the science TV show Cosmos: A Spacetime Odyssey. With more than 2.4 million followers and fewer than 200 citations, the astrophysicist is undoubtedly the top-ranking celebrity scientist on Twitter—and has the highest K-index of anyone on the list. Yet few would consider his Twitter fame unwarranted.

Although the index is named for a woman, Science’s survey highlights the poor representation of female scientists on Twitter, which Hall hinted at in his commentary. Of the 50 most followed scientists, only four are women. Astronomer Pamela Gay of Southern Illinois University, Edwardsville, whose more than 17,000 Twitter followers put her 33rd on the list, says the result doesn’t surprise her because society still struggles to recognize women as leaders in science. Female scientists are also more likely to face sexist attacks online that can discourage their participation, she adds. “At some point, you just get fed up with all the ‘why you are ugly’ or ‘why you are hot’ comments.”

Twitter stardom need not exclude research achievements, as our top 50 Twitter list shows. Many have thousands of citations and seven of the people listed also appear on two recent citation-based rankings of influential scientists, the 2014 Thomson Reuters Highly Cited Researchers list and Scholarometer’s top 100 authors ranking. Even so, most high-performing scientists have not embraced Twitter. Science sampled Twitter usage among 50 randomly chosen living scientists from the Scholarometer list. Only a fifth of the scientists have an identifiable Twitter profile.

Even some who do dislike the medium. Chad Mirkin of Northwestern University in Evanston, Illinois, the highest ranking chemist on Scholarometer’s list, considers Twitter a waste of precious time that he’d much prefer spending on reading and writing scientific papers. “A lot of social media is … time spent aggrandizing one’s accomplishment,” says Mirkin, who registered on Twitter just to keep up with his son’s tennis scores. The linguist Noam Chomsky, the most famous living scientist by some measures, has also repeatedly criticized social media for reducing serious public discourse to, well, 140 characters.

So why do the highly cited researchers who are also Twitter science stars make the time to engage in social media? Geneticist Eric Topol of the Scripps Research Institute in San Diego, California (17th place; 44,800 followers), who boasts more than 150,000 citations, says he once thought the social media platform was only for “silly stuff” like celebrity news. Then he tried Twitter during a TEDMED conference in 2009, as a tool to gauge reactions to his talk. Now, he starts his workday browsing through his Twitter feed for news and noteworthy research in his field. During the day, he checks Twitter several times and spends another 10 to 20 minutes on an evening roundup. “It actually may be the most valuable time [I spend] in terms of learning things that are going on in the world of science and medicine,” says Topol, who reciprocates by daily tweeting papers, presentations, and more to his followers.

Psychologist Daniel Gilbert of Harvard University (36th; 15,500 followers) views Twitter as a natural extension of his other public outreach efforts, which include hosting the PBS science documentary, This Emotional Life. For him, Twitter is a virtual classroom connecting netizens worldwide who are interested in the psychology of happiness. “It’s another teaching tool,” he says.

Like Topol, Jonathan Eisen of the University of California, Davis (25th; 24,900 followers), says he did not start out as a Twitter fan. An enthusiast of open access and exchange, Eisen participated in scientific discussion forums, such as newsgroups, even before the days of the World Wide Web. But Twitter’s 140-character word limit initially seemed both “arbitrary and useless” to him, he says. It was for purely coincidental reasons—checking out details of a visit by famed cyclist Lance Armstrong to Davis, California—that the microbiologist signed up for an account in 2008.

But after 20 minutes of perusing news on the social media platform that day, Eisen says, he was hooked. “In a minute, I can skim through a hundred Twitter posts. … It’s pretty amazing for getting a feel of what’s going on,” says Eisen, who now daily spends anywhere from 5 minutes to 8 hours on Twitter, in addition to running a blog. Yet Eisen also has close to 42,000 citations under his belt.

Eisen says that consistently tweeting ongoing research at his lab has helped attract graduate students as well as two grants for science communication. He suggests an active social media presence might even aid applications for research funding, as it demonstrates a commitment to public outreach. But the spontaneity of Twitter can backfire, too. Eisen, for one, has live-tweeted brusque criticism at academic conferences that came back to bite him. “You can seem like a jerk, an idiot, or both,” he says.

The temporal, attention-grabbing nature of Twitter posts also makes them ill-suited for nuanced, in-depth scientific discussions. Gilbert says he prefers to tweet materials that appeal to a general audience, rather than complex scientific papers. Likewise, Eisen reserves lengthy discussions for old-fashioned phone calls and uses Twitter to instead link to blog posts and other, longer materials.

Still, he and others credit Twitter as a crowdsourcing platform for new ideas and research. Topol says he relies on the “army of Web crawlers” on Twitter to bring him the latest, most noteworthy research in medical science. His own tweets, mostly about papers and presentations he finds interesting, also form an archive that can be extracted with a little tech savvy.

The social media tool also functions as “another dimension of peer review,” Topol says. Instead of waiting for the old letters to the editor, scientists can go to Twitter for rapid critique of their research. “Authors who are not willing to get engaged on social media are missing out on a significant opportunity,” he says.

The K-index gets it wrong by suggesting that science communication and research productivity are incompatible, says Albert-László Barabási, a network theorist at Northeastern University in Boston who studies social media. Research on altmetrics—alternative metrics for measuring scientific impact—has found no link between social media metrics such as number of tweets and traditional impact metrics such as citations, he says. “We should really not mix the two … because they really probe different aspects of a scientist’s personality.”

For his part, Hall says others have read too much into his satire, which originated after seeing conference organizers factor Twitter follower numbers into speaker considerations. “I don’t mean to criticize anyone for having a lot of Twitter followers,” he says. “My criticism is only of using it as a metric on research scientists.”

It might be premature, in any case, for the scientific community to worry about “Science Kardashians” when it faces a more pressing challenge of staying relevant in public discussions. Even Tyson’s Twitter popularity is dwarfed by that of the real Kim Kardashian, who boasts 10 times as many followers.

*SURVEY METHODS

The list of most followed scientists compiled here is far from scientific. To identify Twitter science stars, we began with celebrity scientists such as Tyson and checked out which scientists they followed. We also referenced online lists of scientists to follow on Twitter, such as this one by The Huffington Post. If we’ve missed someone who belongs on the top 50 list, do let us know in the comment section. Follower number is, of course, a very crude proxy of influence on Twitter, but it’s the most accessible metric for the purpose of this story.

The question of who counts as a scientist is itself a matter of debate. As a general guideline, we included only those who have completed a Ph.D. degree and published at least one peer-reviewed paper in a peer-reviewed journal. As an exception to this rule, we excluded professional journalists who fit the above criteria.

We recorded the number of Twitter followers for our list on 15 September. To tally the number of citations for each scientist, we over the past month looked up their Google Scholar profiles or, for those without a profile, used estimates produced by the Publish or Perish software, developed by business professor Anne-Wil Harzing of ESCP Europe. Due to limitations of both methods, the citation numbers are only rough estimates. For example, there’s no easy way to distinguish physicist Brian Cox of the University of Manchester in the United Kingdom from physiologist Brian Cox of the University of Toronto in Canada in calculating the former’s citation count. Seven on our top 50 list appear on either the 2014 Thomson Reuters Highly Cited Researchers list (*) or the Scholarometer’s top 100 authors (+) ranking, and each is noted with a symbol.

The Kardashian Index is calculated as follows: In his commentary, using data gathered on 40 scientists, Hall derived a formula for calculating the number of Twitter followers a scientist should have given one’s citation count. The K-index is the ratio of the scientist’s actual follower number to the follower number “warranted” by the citation count.

An Excel document with all the data collected is here.

The top 50 science stars of Twitter

1. Neil deGrasse Tyson, Astrophysicist

2,400,000 followers @neiltyson

Citations: 151 K-index: 11129

Total number of tweets: 3,962

Hayden Planetarium, United States

2. Brian Cox, Physicist

1,440,000 followers @ProfBrianCox

Citations: 33,301 K-index: 1188

Total number of tweets: 10,300

University of Manchester, United Kingdom

3. Richard Dawkins, Biologist

1,020,000 followers @RichardDawkins

Citations: 49,631 K-index: 740

Total number of tweets: 19,000

University of Oxford, United Kingdom

4. Ben Goldacre, Physician

341,000 followers @bengoldacre

Citations: 1,086 K-index: 841

Total number of tweets: 47,300

London School of Hygiene & Tropical Medicine, United Kingdom

5. Phil Plait, Astronomer

320,000 followers @BadAstronomer

Citations: 254 K-index: 1256

Total number of tweets: 47,000

Bad Astronomy, United States

6. Michio Kaku, Theoretical physicist

310,000 followers @michiokaku

Citations: 5,281 K-index: 461

Total number of tweets: 1,130

The City College of New York, United States

7. Sam Harris, Neuroscientist

224,000 followers @SamHarrisOrg

Citations: 2,416 K-index: 428

Total number of tweets: 2,600

Project Reason, United States

8. Hans Rosling, Global health scientist

180,000 followers @HansRosling

Citations: 1,703 K-index: 384

Total number of tweets: 2,708

Karolinska Institute, Sweden

9. Tim Berners-Lee, Computer scientist

179,000 followers @timberners_lee

Citations: 51,204 K-index: 129

Total number of tweets: 542

Massachusetts Institute of Technology, United States

10. P.Z. Myers, Biologist

155,000 followers @pzmyers

Citations: 1,364 K-index: 355

Total number of tweets: 25,400

University of Minnesota, Morris, United States

11. Steven Pinker, Cognitive scientist

142,000 followers @sapinker

Citations: 49,933 K-index: 103

Total number of tweets: 1,612

Harvard University, United States

12. Richard Wiseman, Psychologist

134,000 followers @RichardWiseman

Citations: 4,687 K-index: 207

Total number of tweets: 22,400

University of Hertfordshire, United Kingdom

13. Lawrence M. Krauss, Theoretical physicist

99,700 followers @LKrauss1

Citations: 10,155 K-index: 120

Total number of tweets: 1,548

Arizona State University, United States

14. Atul Gawande, Surgeon/public health scientist

96,800 followers @Atul_Gawande

Citations: 13,763 K-index: 106

Total number of tweets: 2,118

Harvard University, United States

15. Oliver Sacks, Neurologist

76,300 followers @OliverSacks

Citations: 13,883 K-index: 83

Total number of tweets: 746

New York University, United States

16. Dan Ariely*, Psychologist/behavioral economist

73,000 followers @danariely

Citations: 16,307 K-index: 76

Total number of tweets: 1,091

Duke University, United States

17. Eric Topol*, Geneticist

44,800 followers @EricTopol

Citations: 151,281 K-index: 23

Total number of tweets: 4,966

The Scripps Research Institute, United States

18. Brian Greene, Theoretical physicist

38,700 followers @bgreene

Citations: 11,133 K-index: 45

Total number of tweets: 191

Columbia University, United States

19. Marcus du Sautoy, Mathematician

34,200 followers @MarcusduSautoy

Citations: 1,461 K-index: 77

Total number of tweets: 3,555

University of Oxford, United Kingdom

20. Sean Carroll, Theoretical physicist

33,200 followers @seanmcarroll

Citations: 14,208 K-index: 36

Total number of tweets: 7,295

California Institute of Technology, United States

21. Robert Winston, Fertility scientist

31,900 followers @ProfRWinston

Citations: 7,324 K-index: 43

Total number of tweets: 445

Imperial College London, United Kingdom

22. Bruce Betts, Planetary scientist

28,500 followers @RandomSpaceFact

Citations: 91 K-index: 155

Total number of tweets: 1,619

The Planetary Society, United States

23. Carolyn Porco, Planetary scientist

26,100 followers @carolynporco

Citations: 2,717 K-index: 48

Total number of tweets: 12,700

Space Science Institute, United States

24. Sebastian Thrun+, Computer scientist

25,200 followers @SebastianThrun

Citations: 57,110 K-index: 17

Total number of tweets: 185

Stanford University, United States

25. Jonathan Eisen*, Biologist

24,900 followers @phylogenomics

Citations: 41,289 K-index: 19

Total number of tweets: 46,100

University of California, Davis, United States

26. J. Craig Venter, Genomicist

23,500 followers @JCVenter

Citations: 75,338 K-index: 15

Total number of tweets: 365

J. Craig Venter Institute, United States

27. Vaughan Bell, Neuroscientist

23,500 followers @vaughanbell

Citations: 821 K-index: 63

Total number of tweets: 10,900

King's College London, United Kingdom

28. Robert Simpson, Astronomer

21,500 followers @orbitingfrog

Citations: 2,280 K-index: 42

Total number of tweets: 11,500

University of Oxford, United Kingdom

29. Michael E. Mann*, Meteorologist

20,900 followers @MichaelEMann

Citations: 15,049 K-index: 22

Total number of tweets: 20,000

Pennsylvania State University, United States

30. Jerry Coyne, Biologist

19,500 followers @Evolutionistrue

Citations: 16,657 K-index: 20

Total number of tweets: 7,711

University of Chicago, United States

31. Gary King*, Statistician

19,400 followers @kinggary

Citations: 36,311 K-index: 16

Total number of tweets: 3,080

Harvard University, United States

32. Mike Brown, Astronomer

18,300 followers @plutokiller

Citations: 7,870 K-index: 24

Total number of tweets: 9,764

California Institute of Technology, United States

33. Pamela L. Gay, Astronomer

17,800 followers @starstryder

Citations: 238 K-index: 71

Total number of tweets: 12,700

Southern Illinois University, Edwardsville, United States

34. Jean Francois Gariépy, Neuroscientist

17,700 followers @JFGariepy

Citations: 153 K-index: 82

Total number of tweets: 3,231

Duke University, United States

35. Bob Metcalfe, Computer scientist

16,400 followers @BobMetcalfe

Citations: 424 K-index: 55

Total number of tweets: 16,100

University of Texas, Austin, United States

36. Daniel Gilbert+, Psychologist

15,500 followers @DanTGilbert

Citations: 26,752 K-index: 14

Total number of tweets: 1,294

Harvard University, United States

37. Daniel Levitin, Neuroscientist

15,400 followers @danlevitin

Citations: 5,688 K-index: 22

Total number of tweets: 3,036

McGill University, Canada

38. Andrew Maynard, Environmental health scientist

15,300 followers @2020science

Citations: 10,411 K-index: 18

Total number of tweets: 16,200

University of Michigan Risk Science Center, United States

39. Paul Bloom, Psychologist

15,100 followers @paulbloomatyale

Citations: 14,135 K-index: 16

Total number of tweets: 1,973

Yale University, United States

40. Matt Lieberman, Neuroscientist

14,500 followers @social_brains

Citations: 12,763 K-index: 16

Total number of tweets: 3,088

University of California, Los Angeles, United States

41. Seth Shostak, Astronomer

14,500 followers @SethShostak

Citations: 424 K-index: 48

Total number of tweets: 294

SETI Institute, United States

42. Daniel MacArthur, Genomicist

14,100 followers @dgmacarthur

Citations: 6,884 K-index: 19

Total number of tweets: 15,600

Harvard Medical School, United States

43. John Allen Paulos, Mathematician

14,000 followers @JohnAllenPaulos

Citations: 1,489 K-index: 31

Total number of tweets: 4,144

Temple University, United States

44. Ves Dimov, Immunologist

13,900 followers @DrVes

Citations: 211 K-index: 58

Total number of tweets: 32,200

University of Chicago, United States

45. Simon Baron-Cohen, Psychopathologist

13,600 followers @sbaroncohen

Citations: 84,132 K-index: 8

Total number of tweets: 119

University of Cambridge, United Kingdom

46. Amy Mainzer, Astronomer

13,600 followers @AmyMainzer

Citations: 1,444 K-index: 31

Total number of tweets: 2,221

Jet Propulsion Laboratory, United States

47. Brian Krueger, Genomicist

12,500 followers @LabSpaces

Citations: 154 K-index: 58

Total number of tweets: 36,700

Duke University, United States

48. Karen James, Biologist

12,200 followers @kejames

Citations: 1,007 K-index: 31

Total number of tweets: 61,800

Mount Desert Island Biological Laboratory, United States

49. Michael Eisen, Biologist

11,800 followers @mbeisen

Citations: 68,785 K-index: 8

Total number of tweets: 16300

University of California, Berkeley, United States

50. Micah Allen, Neuroscientist

11,600 followers @neuroconscience

Citations: 81 K-index: 66

Total number of tweets: 21,900

University College London, United Kingdom

Correction, 17 September, 12:22 p.m.: Some affiliations and areas of expertise have been corrected.