One statistic I look at and use in my trading is the amount of time a security trades above or below certain moving averages. One moving average I look at is the 10-day moving average. Right now there are 4 stocks in the S&P 100 that have closed below their 10-day moving average for at least 30 days in a row. They are BAC, RF, GM and WB. Using the current S&P 100, I ran some scans back over the last 10 years to find out how unusual this is.
In the last 10 years there have been only 65 occurrences of an S&P 100 stock closing below its 10-day moving average for 30 days in a row. Twice there have been 4 or more on at once. The first time was in late August of 1998 when there was up to 5 and the 2nd time was early March of 2000 with 4.
From a historical perspective, some of the recent selling, especially in banks and financials, has been persistent to a degree that has rarely been seen.