Subtract lower-price bank repossessions and short sales, and the year-over-year city decline was just 1.2 percent, the data show.
Short sales are those in which the lender accepts a sale price that is lower than the balance of the seller's mortgage, usually as an alternative to foreclosure.
In some parts of the country, eliminating distressed sales turns price losses into gains. In the Washington, D.C., area, for example, CoreLogic says, a 1.5 percent decline became a 3.9 percent year-over-year increase.
Why factor in distressed sales at all? some in the housing industry have asked.
In a recent discussion of his company's quarterly results, Robert I. Toll, executive chairman of the Horsham-based luxury-home builder Toll Bros., said: "We believe that averaging distressed and non-distressed sales data provides a misleading picture to the public regarding home-price direction."
By contrast, Toll said in his statement, "we are experiencing flat to slightly increasing pricing in most markets."
CoreLogic's data bear out Toll's contention. Nationally, May median home prices were down 7.4 percent from the same month in 2010. When distressed sales are removed, the decline is 0.4 percent, just about flat.
"The historic measure we have is for the median price of existing homes, which includes all transactions [traditional and distressed]," said Walt Molony, a spokesman for the National Association of Realtors in Washington.
"Distressed homes only became an issue beginning in 2008, with a downward skew on the overall median, and it's not easy to report separately," he said.
As loan resets work their way through the market, distressed sales will once again become inconsequential within a few years, Molony said.