They Did Their Homework (800 Years of It)

By CATHERINE RAMPELL

THE advertisement warns of speculative financial bubbles. It mocks a group of gullible Frenchmen seduced into a silly, 18th-century investment scheme, noting that the modern shareholder, armed with superior information, can avoid the pitfalls of the past. “How different the position of the investor today!” the ad enthuses.

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.