Heavy refinance activity in the first half of 2015 caused a significant shift in the kinds of single-family MBS produced by Fannie Mae, Freddie Mac and Ginnie Mae. Issuance of MBS backed by adjustable-rate mortgages has dropped sharply in 2015, and ARMs haven’t had much of a presence for years. ARM MBS production by Fannie and Freddie in the first half of 2015 was down 20.1 percent from a year ago. The drop in Ginnie ARM securitization was less severe, 18.3 percent, but ARMs accounted for an even smaller share of overall production (1.7 percent) at Ginnie than the 2.9 percent share they had in government-sponsored enterprise MBS. Oddly, the heavy refinance market in the first half of 2015 did not appear...[Includes two data tables]