Mortgage applications with little documentation were vulnerable to misrepresentation or overestimation of repayment capacity by both lenders and borrowers, perhaps with the expectation that rising house prices would come to the rescue of otherwise unsound loans
«Seasoned» mortgages–mortgages that borrowers have paid on for several years–tend to have higher delinquency rates. That fact, together with the moderation in economic growth, would have been expected to produce some deterioration in credit quality from the exceptionally strong levels seen a few years ago. But other factors, too, have been at work. After rising at an annual rate of nearly 9 percent from 2000 through 2005, house prices have e time, interest rates on both fixed- and adjustable-rate mortgage loans moved upward, reaching multi-year highs in mid-2006. Some subprime borrowers with ARMs, who may have counted on refinancing before their payments rose, may not have had enough home equity to qualify for a new loan given the sluggishness in house prices. In addition, some owners with little equity may have walked away from their properties, especially owner-investors who do not occupy the home and thus have little attachment to it beyond purely financial considerations. Regional economic problems have played a role as well; for example, some of the states with the highest delinquency and foreclosure rates are among those most hard-hit by job cuts in 
the auto industry.
The practices of some mortgage originators have also contributed to the problems in the subprime sector. As the underlying pace of mortgage originations began to slow, but with investor demand for securities with high yields still strong, some lenders evidently loosened underwriting standards. So-called risk-layering–combining weak borrower credit histories with other risk factors, such as incomplete income documentation or very high cumulative loan-to-value ratios–became more common. These looser standards were likely an important source of the pronounced rise in «early payment defaults»–defaults occurring within a few months of origination–among subprime ARMs, especially those originated in 2006.
Although the development of the secondary market has had great benefits for mortgage-market participants, as I noted earlier, in this episode the practice of selling mortgages to investors may have contributed to the weakening of underwriting standards. Depending on the terms of the sale, when an originator sells a loan and its servicing rights, the risks (including, of course, any risks associated with poor underwriting) are largely passed on to the investors rather than being borne primarily by the company that originated the loan. Investors normally have the right to put early-payment-default loans back to the originator, and one might expect such provisions to exert some discipline on the underwriting process. However, in the most recent episode, some originators had little capital at stake and did not meet their buy-back obligations after the sharp rise in delinquencies. 5 Intense competition for subprime mortgage business–in part the result of the excess capacity in the lending industry left over from the refinancing boom earlier in the decade–may also have led to a weakening of standards. In sum, some misalignment of incentives, together with a highly competitive lending environment and, perhaps, the fact that industry experience with subprime mortgage lending is relatively short, likely compromised the quality of underwriting.
In addition, incentive structures that tied originator revenue to the number of loans closed made increasing loan volume, rather than ensuring quality, the objective of some lenders
The accuracy of much of the information on which the underwriting was based is also open to question. Some borrowers may have been misled about the feasibility of paying back their mortgages, and others may simply have not understood the sometimes complex terms of the contracts they signed.