The Beauty Contest That’s Shaking Wall St.

THE extraordinary surge of stock market volatility during the last month can’t be explained by conventional means. Yes, hundreds of scholarly papers have tried to predict the size of such swings, and whole markets — like those for futures and options thrive on these movements. Yet we still don’t have a clear, mathematical understanding of volatility’s source.

Last month, market watchers might have thought they were witnessing a gamma ray burst from outer space, with waves of sudden, crazy noise: On Thursday, Aug. 4, the market, as measured by the Standard & Poor’s 500-stock index, fell by almost 5 percent. The next day was quiet, but the following Monday, the index dropped almost 7 percent. In successive days, it rose 4.7 percent, fell 4.4 percent and rose 4.3 percent. Bigger-than normal changes have persisted since, though they haven’t been quite as drastic.



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