This paper analyzes two complementary measures of tax progressivity. Relative
Share Adjustment (RSA) is the ratio of after-tax to before-tax shares of income for
particular groups. RSAg, a global measure, is the log of RSA averaged over all
groups, weighted by group population. It is equal to the absolute change in
inequality resulting from the tax, as measured by Theil's index of income inequality.
Values for the indexes are computed through application of alternative tax functions
to simulated lognormal income distributions. The results highlight the contrasts in
the distributional effects of different tax structures of similar overall progressivity.
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