富人应该纳多少税才合理?

Do the rich pay their 'fair share' in taxes?

That question is sure to underline much of the political debate in the coming years as the government looks to fill its vast budget hole.

Those on the political left argue that the rich pay a lower share of their income in taxes than the rest of America. We hear stories about rich guys like Frank McCourt, the owner of the L.A. Dodgers, who earned $108 million from 2004 through 2009 but didn't pay any federal or state income taxes thanks to his use of loss-carry forwards. No less than Warren Buffett has complained that his secretary pays more taxes as a percentage of her income than he does.

But an important new paper by economist Greg Mankiw, called 'Spreading the Wealth Around: Reflections on Joe the Plumber,' offers a more factual perspective. He cites Congressional Budget Office calculations that show:

The poorest fifth of the population, with average annual income of $15,400, pays only 4.5 percent of its income in federal taxes. The middle fifth, with income of $56,200, pays 13.9 percent. And the top fifth, with income of $207,200, pays 25.1 percent. The richest 1 percent, with an average income of $1,259,700, forks over 31.1 percent of its income to the federal government.

He concludes that 'it is simply wrong to say we don't have a progressive tax system. The best analysis shows that average federal tax rates rise steeply with income.'

How to account for Mr. Buffett and others? Their calculations often don't include corporate taxes, which would boost the rates.

Of course the rich earn a much larger share of national income today than they used to, with top 1 percent's share of national income more than doubling since the mid-1970s. They also pay a lower tax rate than they used to. There is no denying the rich have gotten richer. (Mr. Mankiw's paper goes on to look at other ways of setting tax rates on the rich, like determining how much value a high-income earner contributes to society or the economy and how much they have benefited from government.)

Yet the important point with the CBO data is that the Warren Buffetts and Frank McCourts of the world don't tell us the whole story of the fair share.

What do you think is a fair percentage for taxing the wealthy?