Brainy, but has he got a really big 'h'?

August 26, 2005

It is the question every academic could soon be dying to ask colleagues: "What's your h-index?"

Jorge Hirsch, a physicist at the University of California, San Diego, developed the index to measure academic worth.

There is some mathematics behind the calculation, but broadly speaking it measures the number of an academic's citations versus the number of academic papers he or she has produced. For example, if an academic has published 50 or more papers, of which 50 have been cited 50 times, then he or she has an h-index of 50.

The index raises the possibility that employers will use this yardstick in assessing potential academic employees or the performance of existing employees.

Professor Hirsch, explaining his reason for creating the tool, said: "In a world of not unlimited resources, such quantification (even if potentially distasteful) is often needed for evaluation and comparison purposes."

Thus far, Professor Hirsch has applied the index only to physicists and biologists. Within a given field, he said, "The person with the higher 'h'

is likely to be the 'better' scientist."

The index avoids the pitfalls of looking only at numbers of papers, which gives no indication of the impact made by the works. It also avoids merely relying on the number of citations per paper, which could reward low productivity or a body of otherwise mediocre work that has been skewed by just one significant highly cited paper.

Professor Hirsch found that those with the highest h-indices were not necessarily those academics who have won major plaudits such as Nobel prizes.

The physicist with the highest h-value was Edward Witten of the Institute for Advanced Study at Princeton, a theoretical physicist who has developed the fields of particle physics and string theory.

Professor Witten's h-index of 110 is higher than that of Nobel laureates Philip Anderson of Princeton University (91), Steven Weinberg of Harvard University (88) and Frank Wilczek (68) of the Massachusetts Institute of Technology.

Stephen Hawking was the highest-rated British physicist, with an h-value of 62, equal to that of the highest-rated woman, Mildred Dresselhaus of MIT.

Professor Hirsch, whose h-index is 49, said that after a 20-year career, an h-index of 20 characterises a "successful scientist", an h-index of 40 describes "outstanding scientists likely to be found only at the top universities or major research laboratories", while an h-index of 60 would show a "truly unique individual".

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