Only twice before over the last century has 5 percent of the national income gone to families in the upper one-one-hundredth of a percent of the income distribution — currently, the almost 15,000 families with incomes of $9.5 million or more a year, according to an analysis of tax returns by the economists Emmanuel Saez at the University of California, Berkeley and Thomas Piketty at the Paris School of Economics.

Such concentration at the very top occurred in 1915 and 1916, as the Gilded Age was ending, and again briefly in the late 1920s, before the stock market crash. Now it is back ....

The new Gilded Age has created only one fortune as large as those of the Rockefellers, the Carnegies and the Vanderbilts — that of Bill Gates, according to various compilations. His net worth, measured as a share of the economy’s output, ranks him fifth among the 30 all-time wealthiest American families, just ahead of Carnegie. Only one other living billionaire makes the cut: Warren E. Buffett, in 16th place.