Existing single-family home prices in 20 major metropolitan statistical areas (MSAs) across the country were down an average 18.5 percent in December 2008 from one year earlier, according to the 20-city composite index released Tuesday by Standard & Poor's. The S&P/Case-Shiller Home Price Index saw another series of record declines, including a fourth-quarter decline of 18.2 percent from the previous year period, the largest quarterly figure "in the series' 21-year history," according to S&P analysts. “The broad downturn in the residential real estate market continues,” said index chairman David Blitzer. "There are very few, if any, pockets of turnaround that one can see in the data. Most of the nation appears to remain on a downward path, with all of the 20 metro areas reporting annual declines, and eight of those MSAs now with negative rates exceeding 20 percent." The December data showed slight improvement in the annualized rates of decline seen in Boston, Denver, Los Angeles, San Diego and Washington D.C. The Sunbelt continued to house the worst performing cities in terms of year-over-year declines: Phoenix was down 34 percent, Las Vegas was down 33 percent while San Francisco fell 31.2 percent. Denver, Dallas, Cleveland and Boston reported the smallest annual declines of 4 percent, 4.3 percent, 6.1 percent and 7 percent, respectively. An overwhelming 18 of the 20 MSAs studied showed double-digit declines from their peak prices, according to the data. Half the MSAs posted declines greater than 20 percent; four of these showed declines in excess of 40 percent. Dallas is down 8.6 percent from its June 2007 peak, while Phoenix is down 45.5 percent from its June 2006 peak. Overall, S&P reported that the data seen in December show that national home prices have crept back to similar levels seen in the third quarter 2003. "If one looks in detail at the annual return data, it can be seen that 13 of the 20 MSAs and the two composites have been reporting consecutive record declines since December 2007," Blitzer said. "The monthly data follows a similar trend, with all of the metro areas reporting at least four consecutive months of negative returns.” Read a media statement regarding the indices. Write to Diana Golobay at diana.golobay@housingwire.com.