The collapse in U.S. home prices accelerated to a record pace in the fourth quarter of 2007, with prices plunging 8.9 percent last year, according to a national home-price index released Tuesday. The quarterly drop in prices of existing single-family homes quickened to 5.4 percent in the final three months of 2007 from a 1.8 percent drop in the third quarter, according to the Standard & Poor's/Case-Shiller National U.S. Home Price Index. In comparison, during the 1990-1991 housing recession, the worst annual performance was a 2.8 percent decline in home prices. The composite index of 10 metropolitan areas fell 2.3 percent in December compared to the previous month and plunged 9.8 percent from a year earlier, which set a new record. The composite index for 20 metropolitan areas fell 2.1 percent in December and fell 9.1 percent from a year earlier. “We reached a somber year-end for the housing market in 2007,” said Yale University economist Robert Shiller, a co-developer of the index. He said home prices across the country and in most metropolitan areas are significantly lower than a year ago. “Wherever you look, things look bleak, with 17 of the 20 metro areas reporting annual declines and the remaining three reporting flat or moderate growth rates,” he said.