A draft paper by Gene Auten of the Treasury Department and David Splinter of the Joint Committee on Taxation finds that income inequality isn't worsening as much as some other economists claim. They conclude:
We start by estimating an improved measure of market income that corrects for tax base changes, adds market income excluded from the individual tax base, such as undistributed corporate profits and employer provided insurance, and adjusts for declining marriage rates. Our measure of consistent market income indicates that between 1960 and 2015 the top one percent income share increased by less than 4 percentage points. Using unadjusted tax-based measures, Piketty and Saez (2003 and updates) estimated that the top market income share increased by 11 percentage points. The most important factors in the difference are accounting for C corporation retained earnings (2 percentage points), corporate taxes and business property taxes (2 percentage points), employer paid payroll taxes and insurance (1 percentage point), and falling marriage rates (1 percentage point)....the top one percent share increased since 1960 from 10.7 to 12.6 percent, about 2 percentage points....The top one percent share of after-tax income increased from 8.5 to 10.1 percent, less than 2 percentage points.
It turns out that tracking this stuff is complicated, and the details matter, which is something to remember the next time you hear some politician or editorial writer make some sweeping claim about dramatically increasing income inequality.