Ed Witten has once again been ranked as the world's number one physicist, according to a new index that ranks scientists in terms of the citations generated from their published papers. The new measure, called the w-index, has been developed by Qiang Wu from the University of Science and Technology of China in Hefei.

Wu's index is similar, but subtly different, to the h-index that was developed in 2005 by physicist Jorge Hirsch at the University of California at San Diego, which quantifies the published output of a scientist.

According to Hirsch's criterion, a researcher with an h-index of, say, 9, indicates that he or she has published at least 9 papers, each of which has been cited 9 or more times. The w-index, on the other hand, indicates that a researcher has published w papers, with at least 10w citations each. A researcher who has a w-index of 24, for example, means he or she has 24 papers with at least 240 citations each.

Wu says in his paper that the index is a significant improvement on the h-index, as it “more accurately reflects the influence of a scientist’s top papers,” even though he concedes that the index could “be called the 10h-index” (arXiv:0805.4650v1).

Tops by both measures

Wu has calculated the w-index for some physicists who also have high h-indexes. Theortical physicist Ed Witten from the Institute for Advanced Study in Princeton, who has the highest h-index, also comes top in the w-index ranking with a score of 41. Witten is followed by condensed-matter theorist Phillip Anderson at Princeton University, with a w-index of 26, and cosmologist Stephen Hawking at Cambridge University coming third with a w-index of 24. Particle theorist Frank Wilczek (Massachusetts Institute of Technology) and Marvin Cohen (University of California, Berkeley) are joint fourth with a score of 23.

While Witten, Anderson and Wilczek also took three of the top five slots in the h-index ranking, the big winner under the new criterion is Hawking, who has a relatively modest h-index of just 62, compared to Witten's score of 110.

According to Wu, a researcher with a w-index of 1 or 2 is someone who "has learned the rudiments of a subject". A w-index of 3 or 4 characterizes a researcher who has mastered “the art of scientific activity”, while "outstanding individuals" are those with a w-index of 10. Wu reserves the accolade of "top scientists" to those with a w-index of 15 after 20 years or 20 after 30 years.

The w-index is easy to work out using a publication database such as ISI Web of Knowledge from Thomson Reuters, Scopus from Elsevier or Google Scholar. It can be determined in the same way as the h-index by simply searching for a researcher's name in a database and then listing all their papers according to citations, with the highest first.