Toward a Better Measure of Horizontal Equity
指出变异系数作为水平公平度量存在局限，提出用税收变异系数与收入变异系数之比（CV Ratio）来改进，并应用于比较现行税制与Armey单一税制的水平公平。
The coefficient of variation (CV), a commonly used measure of horizontal equity, has several important limitations. First, comparing CV for income groups with different average incomes is problematic because groups with larger incomes, by construction, will have lower CV values. Second, groups of unequal width are not comparable because standard deviation can be affected by the interval width. These two limitations make summary measures such as average CV or weighted average CV inadvisable for comparing overall changes in horizontal equity between tax regimes. To remedy these limitations, we propose the ratio of the CV of tax liability to the CV of expanded total income (CV Ratio) for groups of equal width. The advantages of using CV Ratio are demonstrated in an analysis comparing the current tax system and the proposed Armey flat tax system. We observe, using CV Ratio, that there is less horizontal equity at the higher income levels of the current tax system. This is contrary to prior studies using the traditional CV measure.