Are All Ratings Created Equal? The Impact of Issuer Size on the Pricing of Mortgage-backed Securities

We examine whether rating agencies (Moody's, S&P, and Fitch) reward large issuers of mortgage-backed securities, who bring substantial business, by granting them unduly favorable ratings. The initial yield on both AAA-rated and non-AAA rated tranches sold by large issuers is higher than that on similar tranches sold by small issuers during the market boom years of 2004-2006. Moreover, the prices of MBS sold by large issuers drop more than those sold by small issuers, and the differences are concentrated among tranches issued during 2004-2006. We conclude that large issuers receive more favorable ratings and that the market prices the risk of inflated ratings, especially during booming periods.