Yale University economist Robert Shiller, pioneer of Standard & Poor's/Case-Shiller home-price index, said there's a good chance housing prices will fall further than the 30% drop in the historic depression of the 1930s. Home prices nationwide already have dropped 15% since their peak in 2006, he said.

"I think there is a scenario that they could be down substantially more," Mr. Shiller said during a speech at the New Haven Lawn Club.

Mr....