The number of existing homes sold in Washington state increased in the third quarter compared with the previous three months, the Washington Center for Real Estate Research reported Tuesday.

The federal first-time homebuyer tax credit helped sales increase 15.6 percent, according to the center at Washington State University. Sales also were 2.6 percent higher than a year ago, the center said.

It was the first year-to-year improvement in sales since the fourth quarter of 2005.

But the median home price during the July-September period was $260,000, which was 7.6 percent less than a year ago.

"It must be noted that this represents a continued slowing in the rate of decline in prices," said center director Glenn Crellin.

The median price was also held lower because the most active segment of the market was first-time buyers seeking the most affordable homes, he said.

A special study by the center found that about half the home sales in the state during the April-June quarter were to buyers claiming the tax credit, Crellin said. Last week's decision to extend the federal program should help the housing recovery, he said.

Median prices ranged from a high of $515,000 in San Juan County to a low of $125,000 in Adams County.

There were just over 49,000 homes listed for sale with multiple listing services at the end of September, 14.3 percent fewer than a year ago. This was the smallest September inventory since 2006.

While median prices declined, mortgage interest rates increased during the quarter, leaving affordability basically unchanged. The housing affordability index statewide stood at 122.8, meaning the median income family had 22.8 percent more income than the minimum required to qualify to purchase a median price home with a 20 percent down payment and a 30-year mortgage.

WCRER has produced home sales statistics in partnership with Washington Realtors since 1994.