Moody's and S&P Ratings: Are They Equivalent? Conservative Ratings and Split Rated Bond Yields
研究发现，穆迪和标普评级不一致的债券在发行时，穆迪评级较高的债券收益率比标普评级较高的低约8个基点，表明投资者更看重穆迪的保守评级，且1998年后这一效应更强，在透明度低的Rule 144A发行中更明显。
We examine the relative impact of Moody's and S&P ratings on bond yields and find that at issuance, yields on split rated bonds with superior Moody's ratings are about 8 basis points lower than yields on split rated bonds with superior S&P ratings. This suggests that investors differentiate between the two ratings and assign more weight to the ratings from Moody’s, the more conservative rating agency. Moody's becomes more conservative after 1998 and the impact of a superior Moody's rating becomes stronger. Furthermore, the differential impact of the two ratings is more pronounced for the more opaque Rule 144A issues.