Cheaper mortgages are usually a boon to the housing market. But this year, a sharp drop in mortgage rates hasn’t provided much of a lift, and that could bode poorly for the Federal Reserve’s efforts to shore up economic growth.

To see why, take a look at what has happened in housing since mortgage rates began a sharp decline late last year.

Consumer borrowing costs, including mortgage rates, are heavily influenced by the market for government bonds, and yields on those bonds have been falling this year. Similarly, the rate on the 30-year fixed mortgage rate is down more than one percentage point, to 3.75 percen t last week, according to Freddie Mac.

Over the last 30 years, the rate has averaged about 6.25 percent. So the current rates might reasonably have been expected to spark a flurry of refinancing and home buying.