Events surrounding the failure of Lehman Brothers 10 years ago nearly brought down the world’s financial system. While much of the dust has settled, economists and policy makers still seek to better understand the forces that led a set of seemingly small losses on mortgage-backed securities tied to the U.S. housing market to trigger the worst global financial crisis since the Great Depression.
A strong candidate is the series of “runs”—large-scale, rapid withdrawals of short-term funding—that took place throughout 2007-08. The most dramatic run occurred on money market funds (MMFs) immediately following Lehman’s collapse. In a week, investors withdrew more than $300 billion from this market. This figure likely would have been larger had the Treasury not taken the unprecedented step of offering temporary guarantees to MMFs.
What causes runs? One economic theory posits that runs are the result of, and exacerbated by, investors’ self-fulfilling beliefs about other investors’ actions. The nature of banking is fragile. The bank keeps cash on hand to meet depositors’ daily needs, but it will lose money and may fail if it runs out of cash and is faced with the difficult task of selling its loans on short notice. Suppose, though, a depositor is worried a “run” might take place. If she believes that others are asking for their money back she is incentivized to do the same. First out wins; last out loses. If, however, others are not in a panic, that depositor will wait it out and the bank survives.