Mortgage rates experienced their largest one-week decline in a decade last week, according to the latest Freddie Mac Primary Mortgage Market Survey.

For the week ending March 28, the average 30-year fixed rate was 4.06 percent. That was down from the previous week when it averaged 4.28 percent. In just the last four months, 30-year fixed rates have fallen almost a full percentage point, from 4.94 percent to the current rate. A year ago at this time, the average 30-year rate was 4.40 percent.

There was also a significant decline in 15-year rates in the past week. The current survey showed an average rate of 3.57 percent, a drop from 3.71 percent the week before. Last year’s average 15-year rate was 3.90 percent.

The 5-year adjustable-rate mortgage averaged 3.75 percent, a decline from 3.84 the week before. A year ago, 5-year ARM rates averaged 3.66 percent.

“The Federal Reserve’s concern about the prospects for slowing economic growth caused investor jitters to drive down mortgage rates by the largest amount in over ten years,” said Sam Khater, Freddie Mac’s chief economist.

“Despite negative outlooks by some, the economy continues to churn out jobs, which is great for housing demand. We have recently seen home sales start to recover and with this week’s rate drop we expect a continued rise in purchase demand.”