William Calvert (Letters, March 20) is incorrect in suggesting that the triple-A default rates cited by Standard & Poor's are based on the rating immediately before default. They are, in fact, based on the original rating of the security during the period in question. So, of the 26,000 structured securities originally rated triple-A by S&P between 1978 and 2007, fewer than 0.1 per cent subsequently defaulted.
Vickie Tillman
Executive Vice President
Ratings Services
Standard & Poor's
New York, N.Y.
