An extension of the h index that covers the tail and the top of the citation curve and allows ranking researchers with similar h

Citation curves for researchers with the same h index can vary greatly in the heaviness of their top (excess citations to core papers) or the heaviness of their tail (citations to non-core papers), revealing quantitative differences across researchers. Also, promotion to the next higher h depends only on citations received by a small subset of papers, so that researchers with a given h may have citation curves whose top and tail reveal a weaker impact than that of researchers with a lower h. To overcome these problems, we propose a two-sided h index, an extension that computes additional h indices progressively up the top and out the tail of the citation curve. This extension represents a citation curve descriptor one of whose elements is the scalar h. The advantages of the two-sided h index are illustrated through analysis of citation curves for 88 researchers with h indices ranging from 8 to 20. Several schemes are also discussed that use the two-sided h index to define criteria for ranking researchers within and across scalar h indices, according to whether the top of the citation curve, its tail, or both are deemed relevant under the circumstances in which research accomplishments are assessed. (C) 2012 Elsevier Ltd. All rights reserved.