Although the dollar volume of MBS and ABS deals rated by Standard & Poor’s in the first quarter was down from the same period in 2010, the company ranked as the top rating service in both markets, according to a new analysis by Inside MBS & ABS. S&P rated $5.80 billion of non-agency MBS during the first quarter, down 61 percent from its volume in early 2010. But that amounted to 66 percent of total issuance in the market – more than any of its competitors. Overall non-agency MBS issuance was down 50 percent from year-ago levels. Moody’s Investor Services ranked second with $4.5 billion in rated MBS, just over half of the market in... [Includes one data chart]