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English: Share of federal excise taxes paid by US households reporting different income levels, 1979-2007.

Categories renamed to assist in interpretation:

99%-95% is top 5%, minus top 1%. 95%-90% is top 10%, minus top 5%. 90%-80% is top 20%, minus top 10%. 80%-60% is 4th quintile. 60%-40% is 3rd quintile. 40%-20% is 2nd quintile. Lowest 20% is lowest quintile.

Comprehensive household income equals pretax cash income plus income from other sources. Pretax cash income is the sum of wages, salaries, self-employment income, rents, taxable and nontaxable interest, dividends, realized capital gains, cash transfer payments, and retirement benefits plus taxes paid by businesses (corporate income taxes and the employer's share of Social Security, Medicare, and federal unemployment insurance payroll taxes) and employees' contributions to 401(k) retirement plans. Other sources of income include all in-kind benefits (Medicare, Medicaid, employer-paid health insurance premiums, food stamps, school lunches and breakfasts, housing assistance, and energy assistance).

Income categories are defined by ranking all people by their comprehensive household income adjusted for household size—that is, divided by the square root of the household’s size. (A household consists of the people who share a housing unit, regardless of their relationships.) Households with negative income (business or investment losses larger than other income) are excluded from the lowest income category but are included in totals.

Individual income taxes are attributed directly to households paying those taxes. Social insurance, or payroll, taxes are attributed to households paying those taxes directly or paying them indirectly through their employers. Corporate income taxes are attributed to households according to their share of capital income. Federal excise taxes are attributed to them according to their consumption of the taxed good or service.