The multi-dimensionality of journal impact

In recent studies the issue of the relatedness between journal impact factors and other measures of journal impact have been raised and discussed from both merely empirical and theoretical perspectives. Models of the underlying citation processes suggest distributions with two or more free parameters. Proceeding from the relation between the journals' mean citation rate and uncitedness and the assumption of an underlying Generalised Waring Distribution (GWD) model, it is found that the journal impact factor alone does not sufficiently describe a journal's citation impact, while a two-parameter solution appropriately reflects its main characteristics. For the analysis of highly cited publications an additional model derived from the same GWD is suggested. This approach results in robust, comprehensible and interpretable solutions that can readily be applied in evaluative bibliometrics.