The Excess-Tail Ratio: Correcting Journal Impact Factors for Citation Quality
13 Pages Posted: 11 Apr 2012 Last revised: 15 Oct 2012
Date Written: April 10, 2012
Despite widespread adoption, journal impact factors suffer well-known drawbacks that limit their use in accurately and fairly assessing scientific quality. Among these are the extreme variance and skewness in the citations to articles published by a given journal, which results in the sensitivity of impact factors to a few highly-cited articles, and enables many infrequently-cited articles to ‘free-ride’ on citations to these ‘skewed few.’ To address these problems, I adjust journal impact factors according to the relative citedness of the few, highly-cited articles in a journal’s h-core and the many, infrequently-cited articles in its h-tail. I gauge a journal’s citation quality by e^2/Ct, where e^2 captures excess citations above the h^2 citations received by h-core articles, and Ct captures surplus citations received by h-tail articles that do not belong in the h-core. I employ e^2/Ct to correct raw impact factors for 25 management and economics journals. I find e^2/Ct < 1 for all but two journals, consistent with an overstatement of their quality resulting from the sensitivity of impact factors to a few highly-cited articles. Corrected impact factors also yield distinctive and more consistent journal ranking over standard 2-year and 5-year time horizons. I conclude that the ratio of a journal’s excess h-core to surplus h-tail citations is a useful complement to its impact factor, particularly given the increasing use of journal impact factors in the evaluation of scholarly output.
Keywords: h-Index, e-Index, h-Core, h-Tail, Excess-tail Ratio, Journal Impact Factor
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