Uncertainty driven by the current coronavirus outbreak has caused the U.S. stock market to wipe away three years of gains in a matter of weeks. The S&P 500 index fell from 3,386 on Feb. 19 this year to 2,305 on March 20, a loss of 32%. This rate of descent is much sharper than during the initial stages of the Great Recession, when it took from October 2007 to October 2008 to see a similar decrease in the index.