Defining a core: Theoretical observations on the Egghe-Rousseau proposal

In a recent paper EGGHE & ROUSSEAU (2002) have readdressed the problem of defining the "core" of a subject's literature by focussing on the productivity of the contributing sources as measured by their influence on an overall concentration value. Here we generalise Egghe & Rousseau's empirical approach, based upon the Gini index, to a more theoretical setting. This allows a simple visualisation of the geometry of the procedure and a complete analysis in certain classic cases. We conclude that, without additional empirical support, the approach does not appear to offer real improvement on more established and intuitively appealing schemes.