It's been a tough year for the housing market, with sales continuing to slump through the first half of the year.

The Massachusetts Association of Realtors announced Tuesday that sales of single-family homes in May were down 7.5 percent, compared with the same period last year.

The Warren Group, which tracks and publishes real estate data, reported a 9 percent drop in sales of single-family homes during the same period.

Both reports showed home sales falling during the first half of the year on the heels of a big downturn at the close of last year.

The Warren Group, which counts for-sale-by-owner transactions and certain other sales not included in the Realtors' numbers, put the year-to-date decline at 3 percent, compared with less than 1 percent reported by the Realtors' association. May's sharp sales decline "is a pretty good indicator that overall, for home sellers and real estate professionals, this hasn't been the spring they were hoping for," said Terry Egan, editor-in-chief of the Boston-based Warren Group.

According to the Realtor's association, there were 3,884 detached single-family homes sold in May, which represents a 7.5 percent decrease from the 4,200 homes sold the same time last year. The median selling price of a single-family home this May was $355,000, a slight increase compared to $352,700 in May 2006.

The news is better for condominium sales, however, which remain virtually unchanged from the same time last year, according to the association. In addition, prices have gone up due to decreasing inventory, with supply at its lowest level since August 2005, according to the association.

The Warren Group reports a sales dip of 2.1 percent and a 3.5 percent decline in median price, however.

If there's any sign of a turnaround in the state's overall housing market, it's the shrinking glut of homes for sale. The Realtors' group reported a 9.5-month supply of homes for sale in May, down from 11 months of supply in May of 2006 and 15 months last September.

"While tighter lending standards and reduced mortgage options for some prospective buyers this year may have had an impact on the market, stable prices and declining supply indicate there is still a steady demand," said Doug Azarian, president of the Realtors group.

The Warren Group's Egan said the falling inventory of homes for sale isn't necessarily an indicator of a turnaround. Many sellers who don't need to move immediately have taken their homes off the market in hopes of gaining a better sales price by waiting a year or two, he said.

Material from The Associated Press was used in this report.