Imagine if a research career could be summed up in a single number. And imagine further that the number was freely and publicly available. Be careful what you wish for because ... voila, it may appear. Actually, it did appear on November 15, 2005, in the Proceedings of the National Academy of Sciences U.S.A. (102, 16,569-16,572) in a paper by physicist Jorge Hirsch from the University of "California San Diego titled "An Index To Quantify an Individual's Scientific Research Output". Hirsch invented the fa-index, and the world of evaluating scientific contributions has never been the same. In case you've been living under a rock these past 2 years, the fa-index is the number of papers (fa) from an individual's total publications N_p that have been cited at least fa times. Hirsch determined that Nobel Prize winners in physics have an average fa-index of 41, that is, 41 of their papers were cited at least 41 times. The highest fa-index Hirsch could find among scholars in his field went to E. Witten, fa = 110, whereas fa = 62 characterized the famous physicist Stephen Hawking. Of course, there are differences among fields. Disciplines develop different standard practices and cultures; those fields that cite more references in a typical paper or that have more authors per paper will produce greater fa-indices. In particular, life scientists generate large fa-indices, and the highest fa-index for any scientist that Hirsch could find was 191 for S. Snyder, a biologist.
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