Quote from myminitrading:
This is the lightest volume day in quite some time. Volume this week is very light in comparison to last week.
A heavy volume sell off followed by a light volume retracement is not very bullish.
Volume doesn't matter most the time regarding indexes. 1.7 billion versus 2 billion volume isn't a big deal.
The problem with a lot of shorts is they interpret every minor discrepancy as a bearish signal when it isn't. This is why they tend to lose money.