The March Case-Shiller Index was released this week and it corroborates the findings of the government’s most recent Home Price Index — home values are slipping nationwide.

According to the Case-Shiller Index’s publisher, Standard & Poors, home values fell in March from the year prior.

The March report was among the worst Case-Shiller Index readings in 3 years. On a monthly basis, 18 of 20 tracked markets worsened. Only Seattle and Washington, D.C. showed improvement, rising 0.1% and 1.1%, respectively.

On an annual basis, price degradation was even worse.

Washington, D.C. is the only tracked market to post higher home values for March 2011 as compared to March 2010. The national index has now dropped to mid-2002 levels.

As a buyer in today’s market, though, you can’t take the Case-Shiller Index at face value. It’s methodology is far too flawed to be the “final word” in home prices.

The first big Case-Shiller Index flaw is its relatively small sample size. S&P positions the Case-Shiller Index as a national index but its data comes from just 20 cities total. And they’re not the 20 most populous cities, either. Notably missing from the Case-Shiller Index list are Houston (#4), Philadelphia (#5), San Antonio (#7) and San Jose (#10). 

Minneapolis (#48) and Tampa (#55) are included, by contrast.

A second Case-Shiller flaw is how it measures a change in home price. Because the index throws out all sales except for “repeat sales” of the same home, the Case-Shiller Index fails to capture the “complete” U.S. market. It also specifically excludes condominiums and multi-family homes. 

In some cities — such as Chicago — homes of these types can represent a large percentage of the market.

And, lastly, a third Case-Shiller Index flaw is that it’s on a 2-month delay. It’s June and we’re only now getting home data from March. Today’s market is similar — but not the same — to what buyers and sellers faced in March. The Case-Shiller Index is far less useful than real-time data of a city or neighborhood.

The Case-Shiller Index is more useful to economists and policy-makers than to everyday buyers and sellers in Charlotte. For better real estate data for your particular neighborhood, ask your real estate agent for help.

A real estate agent can tell you which homes have sold in the last 7 days, and at what prices. The Case-Shiller Index cannot.

Home values dropped for the sixth straight month in March 2011, according to the Federal Home Finance Agency’s Home Price Index. The Home Price Index is a government-sponsored home value tracker.

The HPI report is the latest in a string of “falling home values” stories — a trend that’s troubling home sellers across Charlotte and nationwide.

However, although the Home Price Index says home values are falling, that doesn’t necessarily mean that they are. Like most statistics in the housing sector, the Home Price Index is plagued by poor methodologies and a lack of timeliness.

In short, the Home Price Index is flawed. In three ways.

The first big flaw in the Home Price Index is that it only measures the values of homes with mortgages backed by Fannie Mae or Freddie Mac. Homes financed via FHA, or via other means are specifically excluded from the calculation. For today’s purchase market, that leaves more than 1 in 4 homes “uncounted” — a big percentage of the market.

Second, the Home Price Index determines home values by measuring price change from sale to subsequent sale. This eliminates new homes — a major market segment.

And, lastly, the Home Price Index reports on a 60-day delay; we’re only now seeing data from March. This two-month lag renders the HPI a trailing indicator for the housing market instead of a forward-looking one. If you’re a home buyer looking for market insight, the HPI can’t give it — it’s out-dated and out of season.

Despite its shortcomings, though, we can’t ignore the Home Price Index completely. It’s among the most thorough home valuation models available, and it’s used in public policy discussions. When the HPI says prices are down, Wall Street and Capitol Hill take notice, and that trickles down to everyday life on Main Street.

Since peaking in April 2007, the Home Price Index is off 19.1 percent.

Consistent with the most recent Case-Shiller Index, the government’s Home Price Index said home prices rose between July and August. 

The Federal Home Finance Agency’s data showed values up 0.4 percent nationwide, on average. Region-by-region, however, the results were scattered. Coastal states tended to perform poorly. Plains states tended to perform well.

A brief look at the regional disparity:

• West South Central : +1.5%
• East North Central : +1.2%
• Pacific : -0.2%
• South Atlantic : -0.2%

Breakdowns like this are important because they highlight the fundamental problem with national real estate data and that’s that home buyers in Charlotte don’t buy real estate in a national market, or even a regional one.

Buyers buy local.

When we look at national figures like the Home Price Index, it’s important to remember that real estate is a collection of tiny markets which, when lumped together, form small markets which, in turn, lump together into larger markets and so forth.

To illustrate this point, a deeper look at August’s Home Price Index data shows that, within the aforementioned Pacific Region, in which home values fell 0.2%, the state of California posted a 2.9% increase. You can be sure that within the state of California, there are cities that performed better than the 2.9 percent, and within those cities, there are neighborhoods that did the same.

Real estate is most definitely local.

That said, we can’t discount the national report entirely. Broader housing statistics like the Home Price Index reflect on the economy and are often used to help shape policy in the nation’s capital. When you need to know what’s happening in your hometown, though, your best source of data is a knowledgeable real estate professional.

Standard & Poors released its Case-Shiller Index Tuesday.  The index is a monthly home valuation report from select cities and among the private sector’s most popular home pricing models.

In reviewing the April Case-Shiller Index and its accompanying analysis, it appears that the housing market’s rebound is gathering momentum.

In the index’s 20 tracked cities:

• 18 of 20 improved from March to April 2010
• Versus April 2009, home prices are up nearly 4 percent
• The two “down” cities from April — Miami and New York — are off just 0.5% and 1.0% annually, respectively

Furthermore, as another sign of strength, San Diego, a city in which homeowners have lost a lot of equity since 2007, has now shown 12 straight months of home price improvement.

However, the Case-Shiller Index must be kept in context. It’s far from perfect.

For one, the index reports on a 60-day delay; it’s only now showing data from the end of April, when the federal homebuyer tax credit was expiring. Home sales have been weak since then it’s been reported.

And second, the Case-Shiller Index is limited to just 20 cities nationwide. Therefore, the index doesn’t consider every home sale in every American city — it only considers a select few. Many more U.S. homes are excluded from the Case-Shiller Index than are included.

But, despite its flaws, the Case-Shiller Index remains important with respect to economic analysis. Much like the government’s Home Price Index, Case-Shiller helps to identify broader trends in housing that shape government and monetary policy.