"This entire conversation is the result of a (largely successful) effort to redefine the debate over taxes from “how much in taxes do you pay” to “how much in federal income taxes do you pay?” This is good framing if you want to cut taxes on the rich. It’s bad framing if you want to have even a basic understanding of who pays how much in taxes.....
That’s really what the American tax system looks like: Not 47 percent paying nothing, but everybody paying something, and most Americans paying between 25 percent and 30 percent of their income — which is, by the way, a lot more [than] the 13.9 percent Mitt Romney paid in 2011*.
When politicians try to convince you that half of Americans aren’t really paying taxes, it’s usually because the real data undermines their preferred policies. For instance, you wouldn’t look at these numbers and think tax cuts for the rich need to be a huge priority. And that’s one reason people who want more tax cuts for the rich don’t like to show you these numbers.
* Romney’s 13.9 percent rate only counts his federal taxes. He hasn’t released his state and local returns for 2011, so we can’t say how that would change his total tax rate. But given the state and local averages for someone in his income group, it’s likely to remain well below the 25-30 percent that is typical."
http://www.washingtonpost.com/blogs/ezra-klein/wp/2012/09/19/heres-why-the-47-percent-argument-is-an-abuse-of-tax-data/