Counting publications and citations: Is more always better?

•Is more always better when counting highly cited publications?•A model of the relationship between scientific impact and citations is introduced.•Having more highly cited publications need not coincide with having more impact.•An improved way of counting highly cited publications is suggested.

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.