Keepin' It Real Estate: How Good is Zillow?

Americans finally get it: Home prices are falling.

This may seem like a preposterous statement, what with the entire global financial system in disarray after the collapse of the US housing market, but we Americans are stubbornly optimistic people, content to ignore calamity as long as we possibly can.

A study released this week by Zillow, a real estate information website best known for its wildly inaccurate estimates of property valies, shows Americans have finally succumbed to the notion that home prices aren't going up anymore. 57% of homeowners polled believe their own home lost value during 2008, up from 38% who felt that way just 6 months earlier.

Interestingly, when asked about the future, respondents were upbeat: Only 30% estimate the value of their house will decrease in the next 6 months. Of course, their neighbors aren’t so lucky: Forty-seven percent believe home values in their local markets will fall during the same time period.

Zillow has become something of a cult phenomenon in the past few years, as it  allows homeowners to go online and see how much their house is “worth.” By its own admission, Zillow’s values are merely estimates based on amalgamating sales data from nearby homes, comparing bedroom counts, living area, lot size and other salient characteristics.

What few people realize, however, is that Zillow’s valuation algorithm isn’t just used by John Q. Homeowner: Every big lender in the country uses a similarly opaque formula to price real estate.

Wells Fargo (WFC) -- now the biggest US home lender in the country after its acquisition of Wachovia -- holds tens of thousands of mortgages on its books, each backed by a unique house. It’s impractical to regularly review each home for a fresh value, so Wells and other big banks like Citigroup (C), JP Morgan (JPM) and Bank of America (BAC) rely on analytics firms to provide property values churned out by what are called Automated Valuation Models, or AVMs.

AVMs rely heavily on recent sales data to drive their valuation estimates. This works reasonably well in a vanilla market, one where home prices move uniformly in a single direction - namely up. Even rapidly rising prices are well accounted for, since liquid markets provide reliable, normal data sets upon which calculations can be made.

AVMs are a bit behind the curve in an appreciating market, offering a conservative estimation of a home’s value. But in a declining, choppy, illiquid market like the one we’re in now, AVMs fall apart.

As sales volume dries up and prices gap down, transactions that are even 3 months old become woefully out of date. Even in distressed markets that are now seeing frenetic buying activity, active listings -- and therefore true market prices -- are well below all but the most recent sales.

By using AVMs to value housing assets, banks are constantly underestimating losses in a declining market. Unfortunately, there isn’t much of an alternative.

Small, independent valuation firms offer the most reliable estimations of value, but they specialize in local markets by definition, which limits the scale with which huge lenders can effectively use their results to evaluate nationwide portfolios of loans.

Next time you laugh at Zillow’s estimation that a home that just sold for $250,000 is really “worth” between $315,000 and $375,000, remember that your bank is looking at the same data. No wonder they keep asking Uncle Sam for so much money.