The researchers’ findings were so striking that they started hunting for mistakes. “We had this result a year ago,” says Ed deHaan, a professor of accounting at Stanford Graduate School of Business. “And we spent the past 12 months scouring every inch of the data and of the model trying to find where we’d done something wrong.”

DeHaan and his colleagues — Suzie Noh, an assistant professor of accounting at Stanford GSB, PhD student Chanseok Lee, and Miao Liu of Boston College — had created an “AI analyst” to study how much an AI bot, using nothing but public information, was able to improve on the performance of mutual fund managers. They were skeptical of the numbers they kept coming up with. But they could find no…