For the 14th consecutive quarter, national US home values declined 3.2% year-over-year during Q210, according to a quarterly market report produced by real estate listing website Zillow. As HousingWire first reported in this week's edition of "Monday Morning Cup of Coffee," the report also found a bit of positive news, as the rate of borrowers underwater on their mortgage declined. The average sales price for residential properties was $182,500 during the quarter, down 0.6% from the Q110 price of $183,700. In Q210, 21.5% of mortgage properties were in negative equity positions, compared with 23.3% in Q110. California markets showed the most improvement, with 10 of the 26 markets surveyed posting year-over-year gains and 20 showing quarter-over-quarter gains. Zillow attributed the Q210 improvement in California to "double tax credits" — the federal and state credits for homebuyers encouraged more buying activity. Of all the 144 markets Zillow tracks, 99 posted year-over-year declines. Markets in Florida and Arizona continue to experience the highest decreases in home prices, with Miami decreased 15.2% and Phoenix down 11.8%, both year-over-year. “As the national housing market limps toward stabilization, individual markets are a mixed bag,” said Zillow chief economist Stan Humphries. “The double tax credits for some California homebuyers have certainly stimulated housing demand there and are partly responsible for the rapid — and likely unsustainable — rates of appreciation in many markets across the state. While there is some uncertainty about how home values will respond in those markets once all incentives are removed, it’s certain they can’t continue at their current rates of appreciation, but is unlikely they will re-test the low points reached in 2009. “Markets in other parts of the country, like Miami and Phoenix, are not yet showing signs of reaching a bottom in home values. High supply continues to be a challenge in states like Florida and Arizona," Humphries added. The home prices for the quarterly report are derived from Zillow's automated valuation model (AVM), which produces a median valuation for all single-family residences, condominiums and cooperatives, regardless of whether the property sold or was listed for sale during the quarter. The top five markets for year-over-year price increases were San Diego (7.3%), San Francisco (5.9%), San Jose (5.6%), Los Angeles (5.5%) and Oklahoma City (5%). The worst five markets for year-over-year price declines were Bend, Ore. (21.8%), Miami and Ocala, Fla. (15.2% each), Detroit (14.3%) and Lakeland, Fla. (13.9%). The markets with the highest rates of negative equity buyers were Las Vegas (71.8%), Merced, Calif. (65.9%), Modesto and Stockton, Calif. (65.5% each) and Port St. Lucie, Fla. (59%). The markets with the lowest rate of underwater borrowers were Cedar Rapids, Iowa (4%), Binghamton, NY (6%), Yakima, Wash. (6.3%) Utica, NY (7.1%) and Pittsburgh (7.3%). In coordination with the release of the report, Zillow posted interactive tools online to track metro and US prices on its website. Write to Austin Kilgore.