They Did Their Homework (800 Years of It)

It ran in The Saturday Evening Post on Sept. 14, 1929. A month later, the stock market crashed.

“Everyone wants to think they’re smarter than the poor souls in developing countries, and smarter than their predecessors,” says Carmen M. Reinhart, an economist at the University of Maryland. “They’re wrong. And we can prove it.”

Like a pair of financial sleuths, Ms. Reinhart and her collaborator from Harvard, Kenneth S. Rogoff, have spent years investigating wreckage scattered across documents from nearly a millennium of economic crises and collapses. They have wandered the basements of rare-book libraries, riffled through monks’ yellowed journals and begged central banks worldwide for centuries-old debt records. And they have manually entered their findings, digit by digit, into one of the biggest spreadsheets you’ve ever seen.

Their handiwork is contained in their recent best seller, “This Time Is Different,” a quantitative reconstruction of hundreds of historical episodes in which perfectly smart people made perfectly disastrous decisions. It is a panoramic opus, both geographically and temporally, covering crises from 66 countries over the last 800 years.

The book, and Ms. Reinhart’s and Mr. Rogoff’s own professional journeys as economists, zero in on some of the broader shortcomings of their trade — thrown into harsh relief by economists’ widespread failure to anticipate or address the financial crisis that began in 2007.