NEW YORK - May 24, 2010 - The housing slump isn't over. Tax credits and historically low mortgage rates have failed to lift home prices so far this year. Prices fell 0.5% in March from February, according to the Standard & Poor's/Case-Shiller 20-city index released Tuesday.

The co-creator of the Case-Shiller index, who predicted in 2005 that the housing bubble would burst, is raising concerns that the worst may still be ahead. That fear is shared by other economists who point to weak job growth, tight credit and many more foreclosures ahead.

"I'm worried still about the risk of a double-dip," economist Robert Shiller said in an interview.

The month-to-month drop from February to March marked the sixth straight decline. Prices in 13 of the cities fell. Only six metro areas recorded price gains. One, Boston, came in flat.

In the first quarter of 2010, U.S. home prices fell 3.2% compared with the fourth quarter.

Prices remain nearly 31% below their July 2006 peak. But they have risen nearly 3% from their April 2009 bottom.

The numbers are especially disturbing because they show that improved sales due to the tax credits didn't translate into higher prices, said David M. Blitzer, Chairman of the S&P index committee.