[Update 1: Adds comment from Robert Shiller] The Standard & Poor’s (S&P)/Case-Shiller US National Home Price Index showed some positive quarterly improvement, gaining 2.9% in Q209 from Q109. It marks the first quarter-over-quarter improvement in three years. But the index was down 14.9% in Q209 from Q208, and the 10- and 20-city composites also saw similar year-over-year declines. Average home prices are now at their early 2003 levels. The 10-city index fell 15.1% between the second quarters of 2008 and 2009 and the 20-city index was down 15.4% over the same period. The rates of decline appeared to slow since last quarter. The national index decline was less than the 19.1% seen between Q109 and Q108, and less than the first-quarter year-over-year declines of 19.4% and 19.1% for the 10- and 20-city indices, respectively. “For the second month in a row, we’re seeing some positive signs,” David Blitzer, chairman of the S&P index committee, said in a statement. “As seen in both seasonally adjusted and unadjusted data, as well as the charts, there are hints of an upward turn from a bottom. However, some of the hardest hit cities, especially in the Sun Belt, show continued weakness.” The 10-City and 20-city composites posted the second consecutive monthly increase in June.  Both were up 1.4% from May to June, and up 0.5% in May over April. All but two of the 20 metro areas — Las Vegas and Detroit — saw improvements in their monthly and annual data. But the recent results doesn’t necessarily mean a bottoming out in the housing market. “We have seen rebounds before that have fizzled,” warned Robert Shiller, co-founder of Case-Shiller Weiss and Yale University economics professor. “It really is too soon to call this a turning point.” Write to Austin Kilgore.

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