The share of pre-tax income accruing to the top 1% of earners in the U.S. has more than doubled to about 20% in 2010 from less than 10% in the 1970s. At the same time, the average federal income tax rate on top earners has declined significantly. Given the large current and projected deficits, should the top 1% be taxed more? Because U.S. income concentration is now so high, the potential tax revenue at stake is large.

But will taxable incomes of the top 1% respond to a tax increase by declining so much that revenue rises...