I settled into my seat for a flight a few days ago from Chicago to Washington, D.C., and opened my book: “What Makes a Terrorist.” I now recognize that this probably wasn’t the best choice of reading material for a crowded plane.

But it is a good read. The author, Princeton economist Alan Krueger, has written an accessible and interesting book on the causes of terrorism. (Disclosure: Krueger was my statistics professor in graduate school; I did badly in the class, which is why I now happily write articles like this that involve no math.)