Les fondements axiomatiques de la mesure des inégalités

It is hopeless to look for an objective measure of inequalities. Indeed, the measure of inequalities depends on citizen?s opinions about justice. It is hence necessary to explicit the ethical fundations of inequality indices. We try, in this note, to present and discuss thoroughly the consequences of the various opinions on which an inequality index may be built. We distinguish two classes of inequality indices. The first one is the class of Atkinson-Kolm-Sen indices, which respect the independence axiom, and implicitely rely on the von Neumann and Morgenstern model. The second one is the class of the Generalized Ginis, which do not respect the independence axiom, and implicitely rely on the Rank-Dependent Expected Utility model. The Ginis indices allow for a thiner representation of citizen?s attitude towards inequality. These indices seem hence of particular interest for evaluating redistributive policies and their adequacy to social objectives.