The 10-city composite index for home prices remained flat in February but was down 2.1 percent for the last three months, according to data released Tuesday by Altos Research LLC and Real IQ. Asking prices on homes fell in 18 of the markets studied, increased in seven markets and remained flat in one. The largest monthly decline in asking prices -- 4 percent -- occurred in Las Vegas, marking the 11th consecutive month of the fastest rate of decline there. The median listing price in Las Vegas fell 36.7 percent from the year-ago period to $206,406 in February 2009. The Houston market posted a 1.6 percent increase for the month, while Miami and Charlotte were up 1.3 percent and 1 percent, respectively. "Pricing trends in these markets appear to be driven by a 'flight to quality' where home buyers focus on a limited supply of the best properties," analysts said in a media statement about the index. House inventory rose by 0.9 percent during February across the 10-city composite, but fell 2.5 percent during the past three months, according to the data. Inventory grew by the largest margin -- 6.7 percent -- in Seattle, while it fell by the largest margin -- 3.1 percent -- in Phoenix. "With housing demand being pummeled by tight credit and job losses, the big question is whether inventory growth will balloon during the spring selling season or remain relatively restrained as it was in February," the report's authors wrote. San Francisco was the only city with fewer days-on-market than 100 in February, while Miami posted the slowest turnover rate at 193 days- (or six months-) on-market. Houses stayed on the market a median 98 days in San Francisco. Write to Diana Golobay at