Single Crossing Lorenz Curves and Inequality Comparisons

Since the order generated by the Lorenz criterion is partial, it is a natural question to wonder how to extend this order. Most of the literature that is concerned with that question focuses on local changes in the income distribution. We follow a different approach, and define uniform $\alpha$-spreads, which are global changes in the income distribution. We give necessary and sufficient conditions for an Expected Utility or Rank-Dependent Expected Utility maximizer to respect the principle of transfers and to be favorable to uniform $\alpha$-spreads. Finally, we apply these results to inequality indices.Inequality measures, Intersecting Lorenz Curves, Spreads

The Ignorant Observer

Most prominent models of economic justice (and especially those proposed by Harsanyi and Rawls) are based on the assumption that impartiality is required for making moral decisions. However, although Harsanyi and Rawls agree on that, and furthermore agree on the fact that impartiality can be obtained under appropriate conditions of ignorance, they strongly disagree on the consequences of these assumptions. According to Harsanyi, they provide a justification for the utilitarian doctrine, whereas Rawls considers that they imply egalitarianism. We propose here an extension of Harsanyi's Impartial Observer Theorem, that is based on the representation of ignorance as the set of all possible probability distributions. We obtain a characterization of the observer's preferences that, under our most restrictive conditions, is a linear combination of Harsanyi's and Rawls' criteria. Furthermore, this representation is ethically meaningful, in the sense that individuals' utilities are cardinally measurable and unit comparable. This allows us to conclude that the impartiality requirement cannot be used to decide between Rawls' and Harsanyi's positions. Finally, we defend the view that a (strict) combination of Harsanyi's and Rawls' criteria provides a reasonable rule for social decisions.Impartiality, justice, decision under ignorance.

The ignorant observer

We propose an extension of Harsanyi's Impartial Observer Theorem based on the representation of ignorance as the set of all possible probability distributions over individuals. We obtain a characterization of the observer's preferences that, under our most restrictive conditions, is a convex combination of Harsanyi's utilitarian and Rawls' egalitarian criteria. This representation is ethically meaningful, in the sense that individuals' utilities are cardinally measurable and fully comparable. This allows us to conclude that the impartiality requirement cannot be used to decide between Rawls' and Harsanyi's positions.Impartiality, Justice, Utilitarianism, Egalitarianism, Decision under ignorance.

Unequal Uncertainties and Uncertain Inequalities: An Axiomatic Approach

In this paper, we provide an axiomatic characterization of social welfare functions for uncertain incomes. Our most general result is that a small number of reasonable assumptions regarding welfare orderings under uncertainty rule out pure ex ante as well as pure ex post evaluations. Any social welfare function that satisfies these axioms should lie strictly between the ex ante and the ex post evaluations of income distributions. We also provide an axiomatic characterization of the weighted average of the minimum and the maximum of ex post and the ex ante evaluations.Inequality; Uncertainty; Multiple Priors

Measuring Inequalities without Linearity in Envy Through Choquet Integral with Symmetric Capacities

International audienceThe (generalized) Gini indices rely on the social welfare function of a decision maker who behaves in accordance with Yaari's model, with a function f that transforms frequencies. This SWF can also be represented as the weighted sum of the welfare of all the possible coalitions in the society, where the welfare of a coalition is defined as the income of the worst-off member of that coalition. We provide a set of axioms (Ak) and prove that the three following statements are equivalent: (i) the decision maker respects (Ak); (ii) f is a polynomial of degree k; (iii) the weight of all coalitions withmore than k members is equal to zero

Fairness under Uncertainty

Ever since its introduction by Foley (1967) and Varian (1974), the notion of fairness has been one of the most extensively used notion to evaluate allocations on an ethical basis. Whereas thereis an extensive literature on the efficiency properties of allocations in economies with uncertainty the concept of an envy-free allocation has not been widely studied in economies with uncertainty. We introduce two very natural notions of equity in an economy under uncertainty, namely ex ante and ex post equity, show they can contradict efficiency requirements. In particular, the set of ex ante efficient and ex post envy-free allocations may be empty. We nevertheless show that, under special circumstances, one may prove the existence of allocations that are both ex ante efficient and ex post envy-free. Such is the case, in particular, in an economy with individual risk and no aggregate risk.

Beliefs and Pareto Efficient Sets: A Remark

We show that, in a two-period economy with uncertainty in the second period, if an allocation is Pareto optimal for a given set of beliefs and remains optimal when these beliefs are changed, then the set of optimal allocations of the two economies must actually coincide. We identify equivalence classes of beliefs giving rise to the same set of Pareto optimal allocations.Beliefs, Pareto Optimality

Fairness under Uncertainty

Ever since its introduction by Foley [1967] and Varian [1974], the notion of fairness has been one of the most extensively used notion to evaluate allocations on an ethical basis. Whereas there is an extensive literature on the efficiency properties of allocations in economies with uncertainty the concept of an envy-free allocation has not been widely studied in economies with uncertainty. We introduce two very natural notions of equity in an economy under uncertainty, namely ex ante and ex post equity, show they can contradict efficiency requirements. In particular, the set of ex ante efficient and ex post envy-free allocations may be empty. We nevertheless show that, under special circumstances, one may prove the existence of allocations that are both ex ante efficient and ex post envy-free. Such is the case, in particular, in an economy with individual risk and no aggregate risk.Fairness, uncerainty, envy

Les fondements axiomatiques de la mesure normative des inégalités

La recherche d'une mesure objective des inégalités, sur le modèle des mesures des grandeurs physiques est vaine : la mesure des inégalités dépend, en effet, de l'opinion des membres de la société en matière de justice distributive. Il est donc souhaitable que les opinions qui sous-tendent les mesures des inégalités soient aussi explicites que possible. Nous nous attachons, dans cette note, à présenter et à discuter en détail les conséquences des opinions sur lesquelles est susceptible de se fonder une mesure des inégalités.Nous distinguons deux classes d'indices d'inégalités, selon qu'ils respectent, ou non, l'axiome d'indépendance. Les premiers sont les indices à la Atkinson-Kolm-Sen, et s'inscrivent dans le cadre du modèle d'espérance d'utilité de von Neumann et Morgenstern. Les second sont les indices de Gini, Gini généralisés et Gini super-généralisés, et s'inscrivent dans le cadre du modèle d'espérance d'utilité dépendant du rang de Yaari ou de Quiggin. Les indices de Gini et ses généralisations permettent une description beaucoup plus fine des opinions en matière de justice redistributive que les indices à la Atkinson-Kolm-Sen, puisqu'ils reposent sur des axiomes plus faibles. Ces indices semblent donc particulièrement bien adaptés pour évaluer l'adéquation des politiques redistributives à des objectifs en matière de justicesociale.mesure des inégalités, attitude à l'égard des inégalités, modèle d'espérance d'utilité dépendant du rang