PHOENIX - Arizona homeowners relieved by the current double-digit increases in values should not count on the trend continuing, a pair of economists warned Thursday.

There could even be a price bubble that might burst and send home prices dropping, though nowhere to the extent of what happened at the end of the last decade, they said.

Marshall Vest of the Eller College of Management at the University of Arizona said the current demand for homes is not coming from people moving here. That's just not happening.

And he said that until the employment situation improves, there's no sign that the kids who moved back in with mom and dad during the recession are in a financial position to form their own households.

What is driving the market, he said, is purchases by investors.

"Some real estate investment trusts have been in here buying up properties with the idea of renting those properties out," Vest said during a meeting at the Capitol of the state's Finance Advisory Committee. That cannot continue forever, he said.

"As soon as they've parked all of the money they have raised, there's a source of housing that's going to go away," Vest said, adding that there is not yet the internal demand to "take up the slack."

Jim Rounds of Elliott Pollack and Associates underlined the role of investors.

In normal times, he said, about 10 percent of all home purchases are for cash. The most recent figures for the Phoenix area, which he tracks, are in the 40 percent range.

Rounds, also a member of the Finance Advisory Committee, also foresees a time when investors are not snapping up Arizona properties. But unlike Vest, he does not see it as a matter of these investment trusts running out of money to buy homes.

"It's them finding additional investment opportunities that are yielding a higher return than hanging on to these homes," he said.

"As you see this steady increase in prices, you're going to start to see opportunities for them to liquidate," Rounds said. "And that will lead to an increase in the supply of available homes."

The good news, he said, is that it no longer looks like the investors will all be dumping their properties at the same time.

"You know how investors go: All of a sudden, two or three people sell and they say, 'We'd better get on this,' " Rounds said.

But he's now predicting a more gradual sell-off.

If prices keep increasing at current rates, however, "you will see a minibubble," he said.

The question, of course, is how much higher things can go - and how much can they fall.

He said home prices already are up 20 to 30 percent from where they bottomed off a year or so ago.

"If you go up another 20 percent, we're looking at a 50 percent increase over a short period of time," he said, a figure even more remarkable when population growth is in the 1 percent-a-year range.

"That bubble hits, you see us go down maybe halfway," Rounds said. A drop of that size is not inconsistent with the historical trend in Arizona, he added. "People get excited," he said. "You have a little bubble. You fall back down."

Rounds said housing prices may be on a "goofy trend" until 2015.

Vest agreed that the 20 to 30 percent price increases of the past year are temporary.

"The best that you can expect would be low- to mid-single-digit increases at some point in the future," he said.

And what of a possible price drop?

"I would hope not," Vest responded, if for no other reason than the rising housing prices have had a beneficial effect on the psychology of consumers and their confidence that things are turning around.

Such confidence is "very healthy for the market," he said. "And I would hope that housing prices don't turn south, again, and destroy all that confidence."