December brought falling prices and decreased inventory to the housing market, according to the Altos 10-City Composite Price Index released Wednesday by Altos Research and Real IQ. Housing prices fell 0.4 percent in December -- bringing the overall fourth quarter decline to 1.2 percent -- as inventory levels also dropped in 25 of the 26 analyzed markets. Asking prices fell at the fastest rate in Las Vegas - down 3.6 percent during December - and 6.8 percent during the fourth quarter.  This marks the ninth consecutive month that Sin City has posted the fastest rate of declining prices among major markets.  Listing prices rose at the fastest rate in Salt Lake City - up 1.0 percent in December.  Charlotte, Dallas and Houston were the only markets that posted three months of sequential price increases. “Prices continue to fall in most major markets but the rate of decline was substantially slower in the fourth quarter than it was during the third quarter,” said Stephen Bedikian, partner and research director for Real IQ.  “The Altos 10-City Composite Price Index declined 2.9 percent during the third quarter but only 1.2 percent during the fourth quarter of 2008.” Detroit was the only major market in which inventory levels did not decline in December.  Across the 10-City Composite Index markets, inventory declined by 6.6 percent in December and 11.4 percent during the fourth quarter.  Inventory fell by the largest amounts in Boston and San Francisco. “Inventory levels have fallen consistently in virtually all markets since the summer of 2008 which is consistent with traditional industry seasonality,” said Michael Simonsen, CEO and co-founder of Altos Research.  “The big question is whether inventory will continue on this declining trend and bring supply and demand back into balance or whether we will see inventory balloon during the spring selling season.” A sign of the treacherous seller's market, the index also found that the median days-on-market rose in all analyzed areas during December, reaching 100 or more days in every major market.  By far, the market with the slowest rate of inventory turnover was Miami at a median of over six months on-market. San Francisco saw the fastest rate of turnover with 100 median days-on-market. Write to Kelly Curran at kelly.curran@housingwire.com. Disclosure: The author held no relevant investment positions when this story was published. Indirect holdings may exist via mutual fund investments. HW reporters and writers follow a strict disclosure policy, the first in the mortgage trade.