  Citation numbers and other quantities derived from bibliographic databases
are becoming standard tools for the assessment of productivity and impact of
research activities. Though widely used, still their statistical properties
have not been well established so far. This is especially true in the case of
bibliometric indicators aimed at the evaluation of individual scholars, because
large-scale data sets are typically difficult to be retrieved. Here, we take
advantage of a recently introduced large bibliographic data set, Google Scholar
Citations, which collects the entire publication record of individual scholars.
We analyze the scientific profile of more than 30,000 researchers, and study
the relation between the h-index, the number of publications and the number of
citations of individual scientists. While the number of publications of a
scientist has a rather weak relation with his/her h-index, we find that the
h-index of a scientist is strongly correlated with the number of citations that
she/he has received so that the number of citations can be effectively be used
as a proxy of the h-index. Allowing for the h-index to depend on both the
number of citations and the number of publications, we find only a minor
improvement.
