MBIA says Ackman's model has major deficiencies

NEW YORK, Feb 14 (Reuters) - MBIA Inc (MBI.N) said that Bill Ackman's estimate that the bond insurer faces more than $11 billion of potential losses is based on faulty assumptions, and is clearly intended to help Ackman's short position in the company.

MBIA said in a letter to regulators dated Feb. 11 and released publicly on Thursday that the model and data Ackman used to determine MBIA's losses appears to "have some major deficiencies," including its use of 1267 randomly selected securities to estimate losses, instead of the loan-by-loan analysis that MBIA uses.

Bill Ackman, founder of hedge fund Pershing Square Capital Management, has been vocal about his short position in MBIA for years. MBIA said in written testimony obtained by Reuters on Wednesday that lawmakers and regulators should curtail the short-sellers beating down its stock, which has fallen more than 80 percent since the start of 2007. (Reporting by Dan Wilchins; Editing by Brian Moss)