A normative and statistical approach to measuring classical horizontal inequity

A local measure of classical horizontal inequity (HI) in an income tax or tax-benefit system is proposed and aggregated into a global index. This index expresses the revenue gain per capita that would come from eliminating HI welfare-neutrally, and also reveals the loss of vertical performance, in terms of the Blackorby and Donaldson (1984) progressivity index, caused by the presence of HI. Non-parametric estimation procedures that can be used to tackle the "identification problem" are delineated. An application to the Canadian tax-benefit system between 1981 and 1994 reveals the changing profile of local HI, its sources, and its aggregate significance.