  In the literature and on the Web we can readily find research excellence
rankings for organizations and countries by either total number of highly-cited
articles (HCAs) or by ratio of HCAs to total publications. Neither are
indicators of efficiency. In the current work we propose an indicator of
efficiency, the number of HCAs per scientist, which can complement the
productivity indicators based on impact of total output. We apply this
indicator to measure excellence in the research of Italian universities as a
whole, and in each field and discipline of the hard sciences.
