Originally Posted by woj

federal income tax is taken out of employees checks and paid to the federal government on employee's behalf, it is NOT payroll tax.. the quoted 47% number, means that for the whole year, net federal income tax paid was zero...

payroll tax is social security + medicare...

in that propaganda piece, err, I mean "study" you posted:
http://www.cbpp.org/cms/index.cfm?fa=view&id=3505

"About half of taxpayers paid no federal income tax last year. It does not mean they paid no tax at all. Many shelled out Social Security and Medicare payroll taxes."

I have no idea which part you find confusing or ambiguous, that quote above is as clear as it gets...