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Top 1% ---- $388,806 ---- 39.89 %
Top 5% ---- $153,542 ---- 60.14
Top 10% ---- $108,904 ---- 70.79
Top 50% ---- $31,987 ---- 97.01
Bottom 50% ---- 2.99
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In 2005 the bottom 40% of Americans by income had an effective negative tax rate: their households received more money through the income tax system than they paid.
http://money.cnn.com/2008/03/31/news/economy/tax_debate.fortune/index.htm?postversion=2008040211
http://www.house.gov/jec/news/2008/July/pr110-45.pdf