Fitch Ratings has finalized its new residential MBS loan loss model, with several additional enhancements designed to better address risks that drive defaults and losses, such as a new variable known as “sustainable loan-to-value,” which represents a borrower’s effective equity in the property. “When gauging credit risk for new U.S. residential mortgage loans, borrower equity is key,” explained Kevin Duignan, group managing director and head of U.S. structured finance for Fitch. “The core principle underpinning the framework is the interaction between borrower equity and market value declines in determining expected loss for...