Higher-earning households are more likely to have fixed-rate mortgages.
Those numbers remind Moskowitz of the day in 2004 when Alan Greenspan, the Fed chairman at the time, said in a speech that Americans were wasting money by getting fixed-rate mortgages, and that banks should encourage more borrowers to get ARMs.
"That surprises me. It shows that poorer people were listening to Greenspan, that ARMs were wonderful," Moskowitz says -- again, half-kidding.
Equity Now's underwriting manager, Matt Hackett, says, "It's a complicated thing, though. It could be people who are younger see themselves as making more money in the future, so they take a five-year ARM and they think they're going to be making more in five years to cover the adjustment."
The proportion of homeowners with fixed-rate loans is likely to keep rising. In the last week of June, fewer than 5 percent of mortgage applicants sought ARMs, according to the Mortgage Bankers Association.
For more information, watch "Poll: We love our homes."