FX & Y, North America

A few years ago three behavioural-finance researchers put a deceptively simple question* to more than 26,000 people—academic economists, ordinary households, retail investors, financial advisers and professional fund managers alike. Suppose a piece of good news about a company’s future earnings is already four weeks old. Should you expect its shares to earn higher returns from here? Most academics said no: around 70% reckoned that month-old news was already in the price, and so told you nothing about the returns to come. Almost everyone else said yes—including about three-quarters of retail investors, two-thirds of financial advisers and, more startling, over half...

This afternoon’s first-quarter results from Nvidia are unlikely to cool the artificial intelligence frenzy. In nominal terms, net income almost certainly grew to a level no public company has ever surpassed. But the chipmaker’s dazzling numbers—and the reaction felt across asset classes—will also illuminate a risk that ought to concern investors and businesses far beyond Silicon Valley: the sheer concentration of global wealth in American technology stocks, and the exposure of the rest of the world to any stumble. Start with scale. American equities are now worth—on paper, at least—$76trn, an amount approaching 70% of world output*. A decade ago...