When Warren Buffet says he only pays a 15% effective tax on his income, that's because his income mainly comes from capital gains and dividends, and he is completely ignoring the fact that the companies he owns must pay a corporate income tax of as much as 35% before he can receive those gains and dividends.
Fortunately, we do have access to facts
that do not distort or color the picture. The chart below uses the numbers as crunched by the Congressional Budget Office. The effective total tax rate
shown is the ratio of total federal taxes (income, social security, corporate, excise)
divided by comprehensive household income. As Greg Mankiw notes, our tax system is highly progressive: "the rich face average tax rates more than twice those of the middle class, and about seven times those of the lowest quintile."
And these effective tax rates include all the benefits of whatever deductions may have been available to individuals and companies along the way.