http://www.brookings.org/es/taxpolicy/facts.htm
For instance, there is a table showing that for the bottom 60% of tax filers, average tax burdens from 1980 to 1999 have gone down (mostly after 1990). For the fourth quintile, the increase is just a tenth of a percent.
Another one, for the bottom 80% of filers, Federal income taxes are less than 9% of income.
And finally, for 74% of families, payroll taxes exceed Federal personal income taxes.
mbs