From Michael Barone at National Review- Equality at the Expense of Prosperity:

But is his picture of current trends complete? The Manhattan Institute’s Scott Winship points out that relying, as Piketty does, on tax returns for the U.S. statistics means omitting income from Social Security, food stamps, public housing, Medicare, and Medicaid. Tax returns count roommates and unmarried partners as separate units when they are part of a larger household. They don’t include employer-paid health insurance — an increasing share of employee compensation in recent decades. Including these factors, Winship notes, means that incomes below the top 10 percent have not stagnated but have risen significantly since the 1970s. Increasing inequality is compatible with increases in ordinary people’s incomes.