Flaws in the Case Shiller Methodology

John Burns

To forecast economic growth, it’s essential to understand the trajectory of the housing market. Most observers rely on widely publicized data like the Case Shiller index, but those metrics can be very misleading if you don’t understand how they are calculated. If you don’t understand that there are factors beyond Case and Shiller’s control that impact the data, according to John Burns, the founder and CEO of John Burns Real Estate Consulting, a 20-person firm based in Irvine, California.

Hedge funds, private equity funds, banks, home builders and real estate developers subscribe to Burns’ market research data to gauge the health of the real estate market.

By surveying over 300 home builders who operate in more than 2,000 cities, Burns gains unique insights into market trends. Each month he asks builders whether their sales are up or down, whether they plan to start construction on new homes, and for their forecast for market conditions.

By contrast, the Case Shiller index relies exclusively on transactional data from home sales, a flawed methodology since less than 0.5% of homes are sold each month. That is too small a sample size from which to make broad conclusions about the housing market, he believes

The biggest problem with Case Shiller is that current market transactions are not representative of overall market trends. “Transactions for the last three years have been concentrated in the rattiest neighborhoods,” Burns said, “where prices are uniformly cheap.” Those are the neighborhoods where sub-prime lending was rampant, leading to tremendous price appreciation in 2006 and resulting in severe price declines over the last two years. The sales volume has been heavily skewed to these neighborhoods, which means that Case Shiller and median price data has been heavily skewed as well.

At the high end of the market there are far fewer listings, a absence of distressed sellers, and no urgency on the part of buyers, according to Burns. Prices at the high end have fallen slowly, and the preponderance of transactions at the lower end of the market distorts the Case Shiller index, causing it to show a more precipitous decline than is really occurring throughout the market.

Demand and supply imbalances are the ultimate driver behind real estate prices, and Burns’ data show the balance is improving, with months of resale supply recently declining from 12 to 10 months. Normally, those inventories are approximately seven months, and until the overhang of unsold homes is reduced, prices will not recover.