Inégalités singulières et plurielles : les évolutions de la courbe du revenu disponible
Authors: Chauvel Louis 
Published: October 2008

Singular Versus Plural Inequalities The Evolutions of the Size Distribution of Income
Louis Chauvel
In many contemporary researches, the multidimensionality of the inequalities is underlined ; nevertheless, our understanding of the phenomenon of economic inequality is often unidimensional. The (popular as well as scientific) representation of inequalities consists of a dichotomical model which refers to two potential worlds : a world of perfect equality where every population member receives the same income, and a world of perfect inequality in which two classes of the population, the poor and the rich, are confronted. Vilfredo Pareto, Max Lorenz and Corrado Gini attempted to build a single indicator for inequality ; therefore they had left us an unidimensional methodological corpus, which is no longer convenient to compare the national differences in the distribution of income : we now know that, even if the income is measured along an unidimensional scale, the problem of its distribution is a multidimensional issue. To go beyond this paradox, we should understand that the distribution of income is not the sharing of a pie between the rich and the poor, but rather between three classes, since the middle class always takes a significant part of the national income. In various western countries, sharing modalities among the three classes lead to various types of distribution. A new method for the analysis of inequality is presented : it is based on the combination of three indicators of inequality respectively for the poor, the middle and the rich classes. These indicators are linked to a specific type of curve, the strobiloid (from the Greek strobilos : tap), allowing the objectivation of the social pyramid, which has in fact the shape of a tap. Such a graphical representation allows a direct comparison of the different national distribution systems and their evolutions. Nowdays, large differences and fast changes appear between the various countries for different years. While our analysis converges to some extent with the shrinking middle class hypothesis, the speed and the extent of such a contraction of the middle class differ among countries. Its consequences on the poor class are also diverse, due to the partial independence between the low and the middle part of the strobiloid : the shrinkage of the middle class may go alongside with the enrichment of the poor — for instance if a more generous minimum income is provided. Such a paradox can not be understood with the classical Gini index, neither with other unidimensional indicators. Moreover, the methodological proposal allows the simulation of the shift of the French strobiloid towards those of Sweden, Netherlands and USA, and the evaluation of the gains and the losses of each class. An important result is the diversity of the shapes of the income distribution curve among western countries. This leads to the refutation of Pareto's idea on the universality of the curve. The actual variety of shapes shows the possibility of a choice in the distribution of disposable income. The curve is not the simple result of an universal deterministic process oriented by the necessities of economic efficiency ; rather, it reveals the equilibrium between confronting social norms.