Fitch Ratings, while telling investors last Friday to expect additional "widespread and significant downgrades" on $139 billion worth of subprime loans, has cited a new factor in their "worsening performance."

"The apparent willingness of borrowers to 'walk away' from mortgage debt," the analysts noted, "has contributed to extraordinary high levels of early default" on loans issued during the 18 months before the mortgage bubble burst. It expects losses to reach 21% of initial loan balances for subprime mortgages issued in...