Everyone knows that all real estate is local.

One neighborhood may be hot, while another one chills. But that fact doesn't answer the eternal real estate question: What's my house worth?

The truth is that no one knows for sure unless they actually put their home on the market and find a buyer. Another way is to have a professional appraisal performed.

But a less expensive alternative exists: Watch the various home price indexes as they hit the headlines.

The Office of Federal Housing Enterprise Oversight, or OFHEO, which produces the highly regarded House Price Index, recently released its figures for the 12 months ending March 31. And the numbers tell a shocking story. In contrast to the screaming declines in value predicted by Robert Shiller of the S&P/Case-Shiller index, these figures showed the average home value in America has not moved up or down in the past year. The study also showed the average home price in metro Atlanta increased by 1.37 percent, 2.2 percent statewide.

Lest you think this index must be somehow flawed, know this: OFHEO's House Price Index tracks average house price changes in repeat sales and refinancings of the same single-family properties. The "all-transactions" index includes more than 35 million repeat transactions and is based on data obtained from Fannie Mae and Freddie Mac for mortgages originated over the past 34 years. The numbers often jump around quarter to quarter, but tend to average out over the period of a year and give a truer picture.

The S&P/Case-Shiller index over the same 12-month period showed a record decline in home prices in its U.S. National Home Price Index of 14.1 percent. That's the number that made headlines nationwide.

So which of these indexes better reflects the true value of your home? To answer, here are some differences in the way the data are collected, as described in an OFHEO analysis:

• The S&P/Case-Shiller indexes only use purchase prices in their calculations, while the OFHEO all-transactions index also includes refinance appraisals. I believe it better reflects neighborhood home values.

• OFHEO's data come from conforming, conventional mortgages provided by Fannie Mae and Freddie Mac. The S&P/Case-Shiller indexes use information obtained from county tax assessor offices in counties and states where that information is available. This is an important difference, because many low-income home sales and most high-end home sales are not included in the OFHEO statistics. In my experience, the sales or refinancings of homes that fall in the middle of the market (loans of $100K to $417K) are most reflective of the average home price movement.

• The S&P/Case-Shiller indexes are value-weighted, meaning that price trends for more expensive homes have greater influence on estimated price changes than other homes. OFHEO's index weights price trends equally for all properties. As stated, I disagree with the value-weighting premise.

• The geographic coverage of the indexes differs. The S&P/Case-Shiller U.S. National Home Price Index, for example, has no value data from 13 states and limited data from others. OFHEO's U.S. index uses data from all states.

The truth is that these two indexes are designed to measure different things, but we consumers only ask one question: What is my house worth today?

Furthermore, you always run into trouble when you apply an average to every instance.

Even though the OFHEO index shows that the average home in Georgia increased in value by 2.2 percent, there is no guarantee that your home went up at all.

In fact, it is possible that your home and neighborhood have had an entirely different experience over that same period.

And that gets us back to the original question of "what's it worth?" In the end, your home is only worth what someone is willing to pay for it on the open market.

If you want to immerse yourself in more real estate sampling data than you might believe could exist, visit my Web site, money99.com, and download the entire OFHEO House Price Index report, all 82 pages of it, for free.

Find previous articles by John Adams and more home buying advice on the

ajchomefinder mortgage center.