STUDENTS can learn a lot about economics when they buy Greg Mankiw’s “Principles of Economics”—even if they don’t read it. Like many popular textbooks, it is horribly expensive: $292.17 on Amazon. Indeed, the nominal price of textbooks has risen more than fifteenfold since 1970, three times the rate of inflation (see chart).

Like doctors prescribing drugs, professors assigning textbooks do not pay for the products themselves, so they have little incentive to pick cheap ones. Some assign books they have written themselves. The 20m post-secondary students in America often have little choice in the matter. Small wonder textbooks generate megabucks.