The fixed-rate mortgage accounts for nine of every 10 loans originated, and it’s easy to see why. Locking into historically low rates makes a lot of financial sense. So who is choosing to buy volatility instead? Who are the 10 percent who still borrow adjustable-rate mortgages? “For some consumers, it’s a better product,” said Frank Nothaft, chief economist at Freddie Mac. “If, for some reason, you know you’ll be leaving your home soon, a 5/1 hybrid ARM is a very fitting instrument. Choosing an ARM could be a matter of timing.” The hybrid ARM is the most common adjustable-rate product...