A Simple Model of Optimal Tax Systems: Taxation, Measurement and Uncertainty

The neglect of administrative issues is a serious limitation of optimal tax theory, with implications for its practical applicability. Under uncertainty, the problems for optimal tax theory are compounded when the full set of tax instruments is neglected. These twin issues are addressed in this paper, by focussing on a fundamental implication of administrative problems, namely, that the tax bases are measured with some error. Consumption taxes can perform the ‘social insurance role of taxation’; a role previously ascribed only to income taxes. A combination of income and consumption taxes can hedge income and measurement-error risks better, relative to the imposition of these taxes alone. The optimal taxes are decreasing in the imprecision with which the corresponding tax base is measured. The taxpayer engages in precautionary savings, in response to uncertainty arising on account of income and measurement problems. Differential commodity taxes, tailored to the measurability characteristics of the different tax bases, dominate uniform commodity taxes. Furthermore, the paper provides a simple, tractable framework for optimal tax theorists interested in diverse kinds of uncertain situations.