“This book is far from all good news.” So writes Tyler Cowen at the beginning of his latest book, “Average is Over: Powering America Beyond the Age of The Great Stagnation.”

Cowen is an economist at George Mason University who is generally classified as libertarian and whose interests range far afield. His most recent books include “The Great Stagnation” and “An Economist Gets Lunch” (his advice: skip fancy downtown places, eat at restaurants attached to Pakistani-owned motels).