Proportional Income Taxation and Effective Progressivity

When incomes are exogenously given, a progressive tax structure reduces inequality in the sense that the Lorenz curve of after tax incomes is nowhere below that of before tax incomes whatever the circumstances as it was shown by U. Jakobsson (Journal of Public Economics 5 (1976), 161-168) The relevance of this standard result is however seriously limited since real-world incomes are determined by the working decisions of the agents in the economy. The paper aims at investigating the implications for effective progression of relaxing the assumption of exogenous incomes when individuals have the same preferences but different talents. We first extend the standard result to the case where agents' working decisions are fully taken into account and we conclude that it is generally impossible to disentangle the respective contributions to inequality reduction of the tax schedule and agents' preferences. We next demonstrate that an elasticity of labour supply which is non-decreasing in productivities is both necessary and sufficient for a proportional tax schedule to result in less unequally distributed incomes. Journal of Economic Literature