You know you’re a serious wonk when you wait eagerly each year for the arrival of the CBO’s “Historical Effective Federal Tax Rates.” But it’s much more than a tax report — it’s the single best estimate we have of trends in income and income inequality.

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Here’s what the numbers say about percentage gains in after-tax income from 2003 to 2005:

Bottom quintile: 2%
Next quintile: 2.4%
Middle quintile: 3.9%
Fourth quintile: 3.7%
Top quintile: 16%

Top 10%: 20.9%
Top 5%: 27.7%
Top 1%: 43.5%

It was a boom, all right — but only for a few people.