Subprime mortgage market turmoil : examining the role of securitization : hearing before the Subcommittee on Securities and Insurance and Investment of the Committee on Banking, Housing, and Urban Affairs, United States Senate, One Hundred Tenth Congress, first session, on how subprime mortgages are securitized, the effect of recent increases in defaults and delinquencies on the subprime securitization market for both borrowers and investors, and how credit risk for mortgage-backed securities is determined and how the assigned ratings are monitored, Tuesday, April 17, 2007.