A 'Subprime' Gauge, in Many Ways?

The article focuses on the December decision of the Swiss bank UBS to write down its subprime mortgage investments by $10 billion more than it had planned, and on the role the ABX index played in the decision. Prior to making the decision the bank looked to the index, which tracks the value of securities backed by subprime home loans, to see whether it should take the additional writedown.