Katz provides Greg Mankiw with some context for remarks quoted in a Wall Street Journal article.

I substantially agreed with Eddie Lazear’s view that a major part of the growth of U.S. earnings inequality is driven by rising returns to skills and the interaction of sharp secular increases in skill demand combined with slower growth in the supply of skills (education) in the U.S in recent decades relative to the past.

(I actually have almost completed book on these themes with Claudia Goldin and a couple new papers making these points: here and here.)