h_α: An index to quantify an individual's scientific leadership
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The α person is the dominant person in a group. We define the α-author of a paper as the author of the paper with the highest h-index among all the coauthors, and an α-paper of a scientist as a paper authored or coauthored by the scientist where he/she is the α-author. For most but not all papers in the literature there is only one α-author. We define the h_α index of a scientist as the number of papers in the h-core of the scientist (i.e. the set of papers that contribute to the h-index of the scientist) where this scientist is the α-author. We also define the h'_α index of a scientist as the number of α-papers of this scientist that have ≥ h'_α citations. h_α and h'_α contain similar information, while h'_α is conceptually more appealing it is harder to obtain from existing databases, hence of less current practical interest. We propose that the h_α and/or h'_α indices, or other variants discussed in the paper, are useful complements to the h-index of a scientist to quantify his/her scientific achievement, that rectify an inherent drawback of the h-index, its inability to distinguish between authors with different coauthorships patterns. A high h index in conjunction with a high h_α/h ratio is a hallmark of scientific leadership.
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