Ratings agency arbitrage

Robert Rosenkrantz writes:

Since the ratings determine required capital, they have a profound influence on how financial institutions invest their assets -- in effect, the regulatory reliance on ratings makes the rating agencies the de facto allocators of capital in our system. And every actor in the financial system has every incentive to group and slice assets in ways that maximize not their fundamental soundness but their rating.

Indeed, that is the entire raison d'être of the $6 trillion structured-finance business, which serves little economic function other than as a rating-agency arbitrage. Subprime mortgages (and all manner of other risky loans) held directly by financial institutions are questionable assets with high associated capital charges. Each one alone would deserve a "junk" rating. Structured finance simply piles such risky assets into bundles and slices the bundles into tranches. The rating agencies deemed some 85% of the tranches by value as AAA, and nearly 99% as investment grade -- thus turning dross into gold by a sort of ratings alchemy.

This ratings alchemy created enormous demand for dross -- in this case, dodgy mortgages. Credit was extended to countless dubiously qualified purchasers of homes, which in turn drove dramatic increases in house prices. The housing bubble has now burst, with average house prices in America down some 20% to 25% from the peak. This led to the current crisis.