Homes were slightly less affordable in March.

A jump in home prices spurred by lower interest rates made the cost of a median-priced home slightly less affordable for the average American family in March, the National Assn. of Realtors reported. The trade group’s monthly index of housing affordability, which measures the ability of the average family to buy a median-priced home, dropped from the February mark of 100.9 to 99.6 in March. When the index is at 100 points, half of American families can afford to buy a home selling for the median price--the point at which half of the homes sell for more and half for less.