Before the collapse of the housing market in 2008, homeowners, particularly younger ones, commonly borrowed against their houses and spent the extra cash. But the idea of homeownership as an investment vehicle has been eroding, as millions find themselves stuck with mortgages worth more than the value of their homes.

"There's a question going forward if people are going to treat houses like piggy banks again," says William Miles, economics professor at Wichita State University, who studied the wealth effect. "It is perhaps questionable we will see as large a housing effect than in the past."

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