Why You Shouldn't Put Too Much Faith In October's Case-Shiller Index

The Case-Shiller Index posted awful numbers in its most recent reading. Each of the index's 20 tracked markets showed home price deterioration between September's and October's respective report. Some markets fell as much as 2.9 percent.

The drop in values is nothing about which to panic, however. The Case-Shiller Index is just re-reporting what we already knew. It's a common theme with the Case-Shiller Index, actually; a trait traced to the report's methodology.

The Case-Shiller Index is an imperfect housing indicator with 3 inherent flaws.

The first flaw is that the index makes use of a limited data set, tracking values in just 20 cities nationwide. That data set is then projected across the more than 3,100 other municipalities in the United States. The "national figures", therefore, aren't really national.

The second flaw is that, even within the tracked 20 cities, not all home sales are included. The Case-Shiller Index only tracks sales of single-family, detached homes, and within that market subset, it only uses homes that are "repeat sales". This specifically excludes sales of condominiums and multi-family homes, and new construction.

Lastly, Case-Shiller Index's third flaw is its "age". The Case-Shiller Index reports on a 60-day delay, and the values it reports are tied to contracts written even longer ago.  Sales contracts from July and August are responsible for October's closings so when we see the Case-Shiller Index as reported in December, some of the data it's reporting is 5 months old already. That's too old to be relevant.

Looking back at 2010, housing was at its weakest between May and August. Therefore, it's no surprise that the most recent Case-Shiller Index shows significant weakness.  Looking forward, we should expect the report to improve -- especially because of how strong New Home Sales and Existing Home Sales have been since summer.

The Case-Shiller Index is helpful for economists and policy-makers. It's not much good for individual homeowners, however. For accurate, real-time housing data, talk to a real estate professional instead.