Turning on tables

The downgrade of billions of dollars of asset-backed securities referenced to US subprime mortgage loans has raised questions about the accuracy of credit ratings. For the new Basel capital Accord, much of which is based on rating inputs, it has raised doubts over certain aspects of the framework. Duncan Wood reports

The Biblical parable of the two builders recounts the contrasting fortunes of two men - a wise man who builds his house on rock, and a foolish man who builds on sand. At first, all seems fine, but then the heavens open, the rain falls heavily and the house on the sand collapses. After building parts of their new regulatory framework upon apparently sound rating inputs, the Basel Committee will be able to empathise: mass downgrades of structured credit deals since July has revealed ratings to be