"To accomplish this goal, we've adjusted all of our ratings to a common set of stress scenarios and definitions, which are embedded in all of our criteria. "Our criteria are subject to regular periodic review across sectors to provide additional transparency and comparability. These improvements are intended to help market participants understand our approach to assigning ratings, enhance the forward-looking nature of these ratings, and enable better comparisons across ratings." Moody's vice president Al Medioli said, "This is why Moody's underwent its recalibration back in 2010, which put all our ratings on a single, universal scale." He added, "Muni default rates are rising although still very low, and recovery rates are now similar to corporates in recent bankruptcies." Both S&P and Moody's have known that default risks of their ratings diverge between corporates and munis since at least the early 1990s, Adelson said.