While the Standar & Poor’s/Case-Shiller Index of home prices gained 1.2 percent in the second quarter from a year earlier and 6.9 percent from the first quarter, Yale economist Robert Shiller, co-creator of the index, isn’t convinced the rebound is here to stay.

“[W]e definitely have positive data,” he tells NPR. “The question is how strong is it and will this rally fizzle? I don't know the answer to that.”

But Shiller notes that this is the fourth spike for home prices since the financial crisis ended in 2009. “It's coming in the summertime, right?” he says.

Editor's Note: Prophetic Economist Warns: “It’s Curtains for America.” See Evidence.

“Well, that's the normal time of strength in the market. So if you look at the data, it doesn't jump out at you that we've reached the turning point.”

That begs the question: How long does the up-trend have to last before it’s taken seriously?

“Once you have a year of solid price increases, you are probably off to the races for some years,” Shiller says

To be sure, housing has a wall of worry to climb. “[T]he pessimism that has surrounded this crisis has caused people to curtail spending,” Shiller. “Governments, businesses and households are all in austerity mode, and that doesn't bode so well.”

But many economists were encouraged by the second-quarter strength of the S&P/Case-Shiller Index.

“Finally, the housing market is forming a bottom,” Pimco CEO Mohamed El-Erian tells Bloomberg. “That should be welcome. It is not surprising because affordability is so attractive right now.”

Editor's Note: Prophetic Economist Warns: “It’s Curtains for America.” See Evidence.