CNN Money:

Robert Shiller, a Yale economist who had argued for years that a bubble was forming in real estate prices, points out that one group was on target about where prices would go - investors in a real estate futures market that he helped set up on the Chicago Mercantile Exchange.

Starting in May 2006, the CME set up futures contracts for 10 metropolitan real estate markets, allowing investors to bet whether prices would go up or down and by how much.

By the end of 2006 those futures were pointing to real estate price declines between 5 percent and 7 percent in those markets, Shiller said. That ended up in line with the 6.7 percent annual decline in the October reading of S&P/Case-Shiller home price index, which was the largest drop recorded in that 20-year-old price measure.

"I'm not normally an advocate of market efficiency, but there's something to be said when you're putting money on the line with your prediction, rather than just talking," he said.

Those futures today are far more bearish about future housing prices than most current economists - foreseeing an additional 4 percent to 14 percent drop in prices over the next year.