“The following tables update the Congressional Budget Office’s (CBO’s) estimates of historical effective tax rates—that is, households’ tax liability divided by their income—for various income categories.1 These new tables incorporate estimates for an additional calendar year, 2006, for the four largest sources of federal revenues—individual income taxes, social insurance (payroll) taxes, corporate income taxes, and excise taxes—as well as the total effective rate for the four taxes combined. The tables also present average before-tax and after-tax household income; counts of households; and shares of taxes, income, and households for each fifth (quintile) of the income distribution and for the top percentiles of households.”