Via WSJ:

The White House’s top economist on Thursday said income inequality in the U.S.  has reached the point where the “middle class has shrunk.” He said the development was “causing an unhealthy division in opportunities, and is a threat to our economic growth,” according to prepared remarks…

The consequence of a shrinking middle class, Mr. Krueger said, was “more families falling into either end of the distribution, and fewer in the middle. The statistical word for this is ‘kurtosis.’ I can see why the term polarization has caught on.”