Fitch Ratings withdrew ratings on 80 subprime bonds within 36 transactions of residential mortgage-backed securities. The ratings agency said the deals no longer held a proper amount of loans. According to Fitch policy, ratings will be withdrawn when the pool of collateralized mortgages falls below 50. It is possible for bonds within the same transaction to maintain their rating as long as the pool of loans stays above 50. On average, the latest rating withdraws come on classes that were issued more than 13 years ago. Mortgages within the pools have been paid down to less than 2% of their original balances. Most of the loans falling out of these bonds liquidated during the foreclosure crisis following the housing collapse in 2008. In February, Fitch reported between 60% and 70% of the subprime mortgages that manage to avoid foreclosure through modification will redefault within one year. Write to Jon Prior. Follow him on Twitter @JonAPrior.