The year-over-year gauge provides better indications of trends in prices, the group has said. The panel comprises Karl Case and Robert Shiller, the economists who created the index.
Nineteen of the 20 cities in the index showed a year-over- year decline, led by a 10 percent slump in Minneapolis. The exception was Washington, where values climbed 4.3 percent.
Prices in 12 markets dropped to fresh lows in March from their 2006, 2007 peaks: Atlanta, Charlotte, Chicago, Cleveland, Detroit, Las Vegas, Miami, Minneapolis, New York, Phoenix, Portland, Oregon, and Tampa.
'Double-Dip'
"This month's report is marked by the confirmation of a double-dip in home prices across much of the nation," David Blitzer, chairman of the Case-Shiller index committee at S&P, said in a statement.
Further declines in home prices are likely to constrain the consumer spending that makes up 70 percent of the economy, as homeowners feel less wealthy and have little home equity to borrow against.
Reports earlier this month showed the housing market remains depressed as the broader economy slows.
Pending sales of previously owned homes plunged 12 percent in April from the prior month, the National Association of Realtors said last week. The gauge measures contract signings, which typically lead closings by one to two months, a sign existing purchases will slow.
Sales Fall
Sales of previously owned homes, based on closings, fell 0.8 percent in April to a 5.05 million rate, with demand for distressed properties accounting for 37 percent of the total, NAR said last May 19.