Newly released data from Ginnie Mae reveal that high prepayment speeds on Ginnie MBS are caused by weak borrower credit quality and high default rates, according to Wall Street analysts. Since 2003, Ginnie MBS has prepaid at significantly higher rates than Fannie and Freddie. While prepayment speeds slowed in the overall MBS market in November, Ginnie pools maintained more pace. In its November prepayment analysis, Bear Stearns said prepayments on 30-year fixed rate mortgages fell…