Aug 16, 2005
A physicist in the US has proposed a new way of quantifying the scientific output of individual scientists. Jorge Hirsch of the University of California at San Diego says that the "h-index" - which is derived from the number of times that papers by the scientist are cited - gives an estimate of the "importance, significance and broad impact of a scientist's cumulative contributions." According to Hirsch the h-index "should provide a useful yardstick to compare different individuals" when recruiting new staff, deciding promotions and awarding grants (physics/0508025).
While the number of papers published by a scientist provides a measure of their productivity, it says nothing about the quality of their work. The number of citations received by a scientist is a better indicator of quality, but co-authoring a handful of articles that are cited widely could "inflate" the reputation of a scientist. Hirsch says that his new approach overcomes these problems. A scientist with a h-index of 10, say, will have published 10 papers that have received at least 10 citations each. The best researchers should therefore have the highest h-indexes.
"A high h is a very accurate indicator of scientific achievement," says Hirsch. "I have looked at the h-index of many physicists in the subfields I am familiar with and have found that there is a very strong correlation between scientists for whom I have a high regard and their high h."
Hirsch says that it only takes a few seconds to find the h-index for a scientist - providing they don't have a common name - on the ISI Web of Knowledge database. For example, the physicist with the highest h-index is the string theorist Edward Witten of the Institute for Advanced Study in Princeton, who has a h-index of 110. This means that Witten has published 110 papers with at least 110 citations each.
Other highly ranked physicists include: Marvin Cohen (94), a condensed matter theorist at the University of California at Berkeley; Philip Anderson (91), a condensed matter theorist at Princeton University; Steven Weinberg (88), a particle theorist at the University of Texas at Austin; and Michael Fisher (88), a mathematical physicist at the University of Maryland (88).
Hirsch, who has a h-index of 49, says that a "successful scientist" will have an index of 20 after 20 years; an "outstanding scientist" will have an index of 40 after 20 years; and a "truly unique individual" will have an index of 60 after 20 years. Moreover, he goes on to propose that a researcher should be promoted to associate professor when they achieve a h-index of around 12, and to full professor when they reach a h about of 18.
However, Hirsch recognizes that the average h-index might be different for different subfields of physics: "One should make sure one knows what the typical values in each subfield are if one is comparing individuals from different subfields," he says.
About the author
Belle Dumé is Science Writer on PhysicsWeb