The MBS (mortgage-backed securities) Index underperformed in November due to quick repayments on higher coupon mortgages as more Americans refinanced into lower-coupons, according to a research report from Barclays.

Refinancing activity generally signals prepayment risk for MBS investors, and the market's high level of refinancing is jarring for higher coupons.

The MBS index lost 49 basis points versus Treasuries and 39 basis points when compared to swaps, the research firm said.  

"The underperformance was driven mainly by spread and offset only slightly by carry," wrote Barclays.