On the heels of rival Standard and Poor's move to adjust its ratings assumptions, which lead to a massive downgrading of RMBS and related securities late yesterday, Fitch Ratings said Thursday that it had enhanced its U.S. RMBS default and loss model, known as ResiLogic. The new model will incorporate 25 new multipliers for specific metropolitan statistical areas (MSAs), the rating agency said, although Fitch did not specify which 25 MSAs it would track via the new multipliers. In the past, Fitch's RMBS modeling employed only state-level risk multipliers, so the new MSA multipliers will certainly enable a stronger regional focus on rating RMBS transactions. There are other changes, as well: apparently, even Fitch's state-level risk multipliers didn't influence loss severity estimates in the past, instead only factoring into an assessment of frequency of foreclosure. The multipliers will modify both loss severity and frequency of foreclosure estimates going forward.