U.S. single-family home prices rose in September and posted their strongest annualized gain in 7-1/2 years, a closely watched survey said on Tuesday.
Robert Shiller, a professor of economics at Yale and a 2013 Nobel laureate, told CNBC he felt the influence of investors in the real estate market played a larger role in the home price increase than the attitude of home-buyers, which Shiller tracks using surveys. A pull-back from the foreclosure crisis could also be driving home prices upward, he said.
"I just don't see evidence that people think we are launching out on some great new era," Shiller said on "Squawk on the Street." "That's what people thought in the early 2000s. Now, they're looking at all the problems in Congress and the fact that Fannie and Freddie are propping up so much of the market."
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Shiller, the co-founder of the Case-Shiller home price index, cautioned that large investment firms buying up real estate, such as Blackstone, may pull out of the housing market once the recovery begins to slow.
"The word from them seems to be that they're long-term investors, but I suspect they're not," Shiller said. "They've learned that there's short-run momentum in the housing market and they know how to play momentum. But as soon as it looks like it's weakening, they'll exit. We can't trust momentum in the housing market anymore."
The S&P/Case Shiller composite index of 20 metropolitan areas gained 0.7 percent in September on a non-seasonally adjusted basis, matching the Reuters forecast.
"Housing continues to emerge from the financial crisis: the proportion of homes in foreclosure is declining and consumers' balance sheets are strengthening," David Blitzer, chairman of the index committee at S&P Dow Jones Indices, said in a statement.
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"The longer run question is whether household formation continues to recover and if home ownership will return to the peak levels seen in 2004."
Prices in the 20 cities rose 13.3 percent year-over-year, the strongest gain since February 2006, topping expectations for a 13 percent year-on-year advance.
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—By Reuters. CNBC contributed to this report.