Prices for existing homes in many of the country's major markets continued to slip in June, according to the latest S&P/Case-Shiller Index, which tracks existing home prices in 20 metros to arrive at a composite index for each. June was the 16th consecutive month in which the Index was lower than the previous month.

In June, the Index fell to 167.69, off marginally from 168.54 index for May, but 15.9 percent below the June 2007 index of 199.44. As expected, markets where foreclosure sales activity is rampant have experienced greater erosion in existing home prices. For example, the June Index in Phoenix, 153.19, was 27.9 percent below the same month a year ago. In Las Vegas, the year-to-year index fell 28.6 percent to 158.51, and by 24.2 percent in San Diego. Existing-home prices in condo-glutted Miami were off 28.7 percent in June from a year ago.

Conversely, prices in June held a bit better in Denver, Atlanta, Chicago, Boston, Minneapolis, Charlotte, New York, Cleveland, and Dallas, all of which had higher indexes than in May 2008, and have experienced milder price declines over the previous 12 months.

The S&P/Case Shiller Index reports steeper price declines than estimates released yesterday by the National Association of Realtors, which show that the median price of an existing home sold in June was off 7.1 percent from a year ago, to $212,400. The accuracy of the Case-Shiller Index was questioned a few weeks ago in the Washington Post, where three academics pointed out that the Index does not track prices in 13 states and offers only partial data for 29 others. The writers (two of whom teach at Wichita State University in Kansas) also noted that the Index gives more weight to higher-priced homes, meaning "it is particularly sensitive to what is happening with high-priced homes in the largest, most expensive markets." The writers suggest that government data from the Office of Federal House Enterprise Oversight, whose latest estimates are released later this morning, present a more balanced and less exaggerated picture of existing housing price swings.

At the very least, it's still worth noting that existing home prices continue to vary widely by market and region. The Florida Association of Realtors recently noted, for example, that home prices in Palm Beach County fell to a four-year low in July to $291,300, which was 22 percent below the July 2007 median.

Learn more about markets featured in this article: Atlanta, GA.