Abstract: The rise and fall of subprime mortgage securitizations contributed in part to the ensuing credit crisis
and financial crisis of 2008. Some participants in the subprime-mortgage-backed securities market relied at least
in part on analyses grounded in the loss development factor (LDF) method, and many did not conduct their own
credit analyses, relying instead on the work of others such as securities brokers and rating agencies. In some
cases, the parties providing these analyses may have lacked the independence, or at least the appearance of it, that
would have likely better served the market.
A new appreciation for the value of independent analysis is clearly a silver lining and an important lesson to be
taken from the crisis. Actuaries are well positioned to lend assistance to the endeavor.
Mortgages are long-duration assets and, similarly, mortgage credit losses are relatively long-tailed. As casualty
actuaries are aware, the LDF method has inherent limitations associated with immature development. The
authors in this paper will cite examples of parties relying on the LDF or similar methods for projecting subprime
mortgage credit losses, highlight the limitations of relying exclusively on such methods for projecting subprime
mortgage credit performance, and conclude by offering general enhancements for an improved approach that
considers the underwriting characteristics of the underlying loans as well as economic factors.