  Is more always better? We address this question in the context of
bibliometric indices that aim to assess the scientific impact of individual
researchers by counting their number of highly cited publications. We propose a
simple model in which the number of citations of a publication depends not only
on the scientific impact of the publication but also on other 'random' factors.
Our model indicates that more need not always be better. It turns out that the
most influential researchers may have a systematically lower performance, in
terms of highly cited publications, than some of their less influential
colleagues. The model also suggests an improved way of counting highly cited
publications.
