Paul Caron notes that:
From the JEC abstract:
IRS data for 2003, the most recent available, show that the top half of taxpayers ranked by income continue to pay over 96% of Federal individual income taxes while the bottom half accounts for just less than 3.5%. The data show the highly progressive nature of the Federal income tax.
Well... Actually, no it doesn't show that. To measure progressivity we need to know what percentage of total income is earned by the top half of taxpayers. The JEC doesn't provide income distribution data in the report. Without that data, the data they do provide doesn't really tell us much.