Jack M. Guttentag The Mortgage Professor

In the first article of this series, I pointed to the ending of house-price appreciation as the immediate cause of turmoil in the subprime market. The rise in delinquencies, defaults, and foreclosures has been concentrated among appreciation-dependent mortgages -- those that work for borrowers only if their properties appreciate. A large proportion but not all of such mortgages are subprime.

While it is understandable that borrowers became caught up in the belief that house prices always rise, lenders are supposed to know better. Why was the mortgage-lending industry willing to make loans that were workable for the borrowers only if their properties appreciated?

Disaster Myopia

In 1986, with my colleague from Wharton, Richard Herring, I published an academic paper called "Disaster Myopia in International Banking." The paper set out to explain the international banking crisis of the early 1980s, but on rereading it recently, I realized that it also goes a long way toward explaining the current crisis in the subprime market.

The disaster myopia thesis is that, if potential shocks that can cause major losses to lenders occur very infrequently, they will not be fully reflected in loan prices and conditions. If the market is competitive and some lenders are willing to discount the likelihood of a shock altogether, other lenders who might be inclined to be more cautious are forced to go along or lose market share.

In the mortgage market, disaster myopia meant basing mortgage prices and underwriting rules on the assumption that, because house prices had risen for a very long period, they would continue to rise. The cessation of price increases was thus a shock for which lenders were no better prepared than borrowers.

Disaster myopia was especially prevalent among aggressive subprime lenders who could make a lot of money in a very short time so long as house prices kept rising. Other subprime lenders who might not be disaster myopic were forced to operate as if they were, in order to remain competitive.

Underwriting requirements in the subprime market are set by the investment banks that buy the loans and securitize them. While the investment banks may or may not have been disaster myopic, those that were willing to accommodate the more aggressive lenders did more business (so long as house prices were rising) than those who insisted on maintaining more-restrictive underwriting rules.

Mortgage Market Shocks Spread

Virtually all subprime mortgages are converted into mortgage-backed securities that are sold to investors. These securities are actively traded and are therefore under constant surveillance by investors, traders, and rating agencies. Bad news about defaults surfaces quickly and is rapidly reflected in lower market prices of securities. The value of loans in the pipeline -- on the way to securitization but not there yet -- also drops.

The rapidity with which the current crisis in the subprime market has spread marks a very important difference from the international banking crisis of the 1980s. The international banks kept virtually all the "bad" international loans in their own portfolios, and they used various stratagems for keeping the original values on their books unchanged.

This avoided widespread failures, but it also shut down the market for new loans.

The Failure of Lenders

As of May 1, 2007, "National Mortgage News," a trade publication, counted 32 subprime lenders that had become "defunct" since early 2006. The immediate cause of most of the failures was the reduction in the market value of the loans in their pipelines -- loans they had already purchased but not yet sold.

Lenders originate mortgages in preparation for sale mainly with borrowed funds; their capital is usually quite small. Most borrowed funds come from what are called "warehouse lenders," mainly large commercial and investment banks, who protect themselves by requiring that the unsold mortgages be posted as collateral. When the value of the collateral drops, the account becomes "under-margined" and the warehouse lender asks for more collateral. If the decline in the value of the mortgages exceeds the capital of the subprime lender, the latter will be unable to comply and probably will be forced to shut its operations.

A marked deterioration in the payment experience of subprime borrowers poses a second threat to the solvency of subprime lenders. Under their arrangements with investment banks, lenders are required to repurchase loans that become delinquent within a few months after sale. The more aggressive the lender in pushing through marginal cases, the more buybacks they are likely to face. Collateral calls and buybacks are the major causes of lender failures.