"As with the average federal tax rates for all taxes, average federal tax rates for the individual income tax have declined for the lowest three income quintiles since the early 1980s... The extent of the decrease was greatest for the lowest quintile, for which the rate dropped by nearly 7 percentage points... Average tax rates that are less than zero for the bottom two quintiles... about 35 percent of households did not owe any federal income taxes..."  Congressional Budget Office, Dec. 2, 2010.