N. Gregory Mankiw, What the President Could Learn From Professional Economists, New York Times, March 10, 2017

A second cause of slower economic growth is the decline in productivity growth, which has occurred not just in the United States but in most advanced economies. The reason for this slowdown is not fully understood, but I recently heard one explanation at a seminar given by the Stanford University economist Charles I. Jones.

According to a recent paper by Mr. Jones and three co-authors, the number of Americans engaged in research has increased more than twentyfold since the 1930s, yet there has been no similar explosion in productivity growth. Their interpretation is that big ideas are just getting harder to find. Unfortunately, there is no sign that this is about to change.