Banks' share prices have become "hostages to the vagaries of ABX benchmarks" in the view of one analyst team, because the indexes, which are used to value financial institutions' holdings in mortgages and other credit investments, have dropped farther than economic conditions in the US housing market justify.

Writedowns by banks on the value of their structured credit holdings have contributed to sharp drops in the ABX indexes, which track derivatives linked to mortgage bonds. Since the beginning of July, the 2007-2 series of AAA-rated sub-prime collateralised debt obligations, the tranche rated the highest quality, has slumped to about 70% of face value.