Over the last two days the S&P 500 has gained a staggering 4.48%. That’s more than half of the return one might expect in an average year…in only two days! To put that into perspective, the chart below shows the two-day percentage change in the S&P 500 with plus and minus three standard deviations overlaid. That is three standard deviations, not two which is a rare occurrence in itself. The probability of a normally distributed series coming in more than three standard deviations above the mean is .0015% or a 1 in 666 chance.
