First-time defaults on private mortgages edged up to a rate of 0.89% in October, a slight increase from this segment's default rate of 0.86% in September, a new report from Amherst Securities Group said Friday. The nonagency securitized mortgages are grouped in the "always performing category" were valued at $565.1 billion last month, down more than $200 billion from $727.5 billion a year earlier. The annual default rate for 2007 option adjustable-rate mortgages in the non-agency segment grew to 23.9% in October, compared to 21.6% in September. Meanwhile, 2006 subprime hybrids hit an annual default rate of 23.8% in October, compared to 22.3% in September. Overall, voluntary prepayments were lower in October, with prepayment speeds on 2007 prime collateral dropping the most. Prime fixed-rate loans prepaid at a rate of 13.6% per annum in October, a decline from 14.7% in September. In October, 2007 prime hybrid loans prepaid at a rate of 15.8% last month, down from 16.6% in September. "We expect lower driving rates to be reflected in higher prepayment speeds next month," Amherst Securities concluded in its latest study. Amherst attributes the decrease in voluntary prepayments to the fact that September was a relatively short month. "As a result, payments due at the beginning of the month, and sent in later in the month, are less apt to be processed in a month with fewer business days. Similarly, borrowers have fewer days to have refinancings completed, thus voluntary prepayments tend to be lower," Amherst wrote in its report. Write to Kerri Panchuk.