Measuring scientific performance without ties: Is scientific leadership the solution?

For many decisions in science, evaluators have to select, assess, and rank authors based on their scientific achievements. However, the most diffused scientific performance bibliometric metric – the h index – produces many ties, precluding its use to define a full ranking of the authors. In turn, recently, Jorge Hirsch proposes the h-alpha index (which measures the number of papers of the h core in which the author was the scientific leader)and the associated r-alpha index(percentage of papers belonging to the h core in which the author was leader)to capture the concept of scientific leadership. We suggest using this last measure to break the ties of the h index. The method is extremely simple and provides a complete solution to this critical problem of the h index. To that end, we develop a two steps procedure, which is able to produce a more granulated ranking of the authors.