Until 2002, according to Yale University economics professor Robert Shiller, the phrase “housing bubble” was hardly ever mentioned in the pages of this country’s major newspapers.

And, then, the number of times it was used began to skyrocket.

Indeed, to the casual observer, a graph plotting the number of mentions of “housing bubble” over the last 30 years shows all the telltale signs of a bubble -- a long relatively horizontal line followed by a huge spike upwards.

And, yet, we will never know for sure whether housing is currently in a bubble unless real estate prices eventually plunge. Until then, it will be the subject of endless speculation -- and great fodder for journalists and columnists.

Professor Shiller himself is in the “housing is in a bubble” camp. But, at an early-May conference at Yale, he presented data that I think can help reframe the debate in some helpful ways. (The conference, “Behavioral Finance for the Quantitative Equity Practitioner,” was put on by the International Center for Finance at the Yale School of Management.)

Instead of asking whether housing is in a bubble, for example, why not ask which regions of the country are showing more or fewer signs of bubble-like behavior?

The virtue of this reframed question is that it focuses our attention away from black and white categorizations and toward determinations of relative value. And, once we do that, I think most of us can agree that real estate in certain parts of the country is more overvalued (or less undervalued) than in others.

Contrast real estate in Los Angeles with Milwaukee’s, for example. For a number of years, Professor Shiller has been conducting surveys of attitudes toward real estate in several cities, including these two.

One of the questions his survey asks: “On average, over the next 10 years, how much do you expect the value of your home to change each year?” In the latest survey, respondents in Los Angeles, on average, said "22.5%," while those in Milwaukee said "13.4%."

Regardless of whether you think these numbers reflect a bubble mentality in an absolute sense, I think we can agree that the expectations of Los Angeles residents make its real estate market far more vulnerable to a crash than Milwaukee’s.

A number of other questions in Professor Shiller’s survey point to the same conclusion. For example, one of the other questions in the survey says, “In conversations with friends and associates over the last few months, conditions in the housing market were discussed.” Two-thirds of the Los Angeles respondents said that such conversations were frequent, compared to only a sixth of the Milwaukee respondents.

From the data, Professor Shiller concludes that there is a “high likelihood of an eventual decline in Los Angeles” real estate while there is “relatively little risk in Milwaukee and other stable cities.”

The investment implication is clear: Your odds of success are greater when investing in the real estate of cities like Milwaukee than they are when investing in that of cities like Los Angeles.

Mark Hulbert is editor of the Hulbert Financial Digest, a service of Marketwatch that, for nearly 24 years, has tracked the performance of investment advisory newsletters. A section of the Marketwatch website called "Hulbert Interactive" (marketwatch.com/hulbertinteractive) allows users to conduct extensive research on the HFD database.

Mark can be contacted via email at mhulbert@marketwatch.com