Standard & Poor’s Claims Top Ranking in Both Non-Agency MBS and Non-Mortgage ABS Ratings Standard & Poor’s continued to dominate the non-agency MBS rating business in 2003, stamping some 93.5 percent of new issuance with its credit grades over the course of the year. A new Inside MBS & ABS analysis indicates that S&P’s dominant role in the 2003 non-agency MBS market was based in large part on a huge presence in the subprime market.