From a reader, re: today’s WYP :

Fascinating discussion with Peter Beinart on income inequality. You might be interested in the chart at the end of this post, which compares the situation in Europe with the situation in America.
Also, I heard you say that a case can be made that the middle class has fallen behind over the years. I don’t get that. Look at the middle-income, after-tax income chart toward the bottom of this post. The values are adjusted for inflation, and what you see is steady progress for those in the middle over the years.
Income inequality is a hard problem because, as you said (and as that New York Times article acknowledged), it correlates with prosperity for everyone (except, perhaps, for those at the very bottom of the scale).