It’s not the size of the decline but the speed with which investors are hitting sell buttons. At one point today some 89 percent of stocks on the New York Stock Exchange traded in the red, surpassing the threshold reached Dec. 24, when a 2.7 percent rout in the S&P 500 pushed the gauge to a 20-month low. During the December correction, the volume of stocks trading down was higher just on one other day, Dec. 4.
