Seasonal trends hit the GSE single-family mortgage-backed securities business in November, with new issuance of single-family MBS tumbling 15.1 percent from October. A new Inside the GSEs analysis of loan-level MBS disclosures reveals that a sharp 22.0 percent drop in securitization of purchase-money mortgages was the major factor in the November decline. Refinance loans delivered to Fannie Mae and Freddie Mac MBS pools were off a milder 6.8 percent from the previous month. In fact, more than half of Fannie’s MBS flow in November came from refinance loans, the first time since March that purchase mortgages accounted for less than half of the GSE’s business. One sign of the increased refinance share of GSE business ... [with two exclusive charts]