Possible Duplicate:
How will going from 75% Credit Utilization to 0% Credit Utilization affect my credit score?
I've read in a few places some statistics to indicate that people with zero CC balance have a lower average credit score than someone who maintains a low, yet nonzero, balance. What is the mechanism of this, if it is actually a real effect? Another possibility could be that those with zero balances don't use credit and don't have a significant credit history, leading to a lower score.