Zillow off a median of 8% on home prices; is this a big problem?

Zillow’s CEO recently discussed the error rate of his company’s estimates for home values:

Back to the question posed by O’Donnell: Are Zestimates accurate? And if they’re off the mark, how far off? Zillow CEO Spencer Rascoff answered that they’re “a good starting point” but that nationwide Zestimates have a “median error rate” of about 8%.

Whoa. That sounds high. On a $500,000 house, that would be a $40,000 disparity — a lot of money on the table — and could create problems. But here’s something Rascoff was not asked about: Localized median error rates on Zestimates sometimes far exceed the national median, which raises the odds that sellers and buyers will have conflicts over pricing. Though it’s not prominently featured on the website, at the bottom of Zillow’s home page in small type is the word “Zestimates.” This section provides helpful background information along with valuation error rates by state and county — some of which are stunners.

For example, in New York County — Manhattan — the median valuation error rate is 19.9%. In Brooklyn, it’s 12.9%. In Somerset County, Md., the rate is an astounding 42%. In some rural counties in California, error rates range as high as 26%. In San Francisco it’s 11.6%. With a median home value of $1,000,800 in San Francisco, according to Zillow estimates as of December, a median error rate at this level translates into a price disparity of $116,093.

Thinking from a probabilistic perspective, 8% does not sound bad at all. Consider that the typical scientific study works with a 5% error rate. An eight percent error rate suggests the estimate is right 92% of the time. As the article notes, this error rates differs across regions but each of those have different conditions including more or less sales and different kinds of housing. Thus, in dynamic real estate markets with lots of moving parts including comparables as well as the actions of homeowners and homebuyers, 8% sounds good.

Perhaps the bigger issue is what people do with estimates; they are not 100% guarantees:

So what do you do now that you’ve got the scoop on Zestimate accuracy? Most important, take Rascoff’s advice: Look at them as no more than starting points in pricing discussions with the real authorities on local real estate values — experienced agents and appraisers. Zestimates are hardly gospel — often far from it.

Zillow can be a useful tool but it is based on algorithms using available data.

Zillow back with Trick or Treat ratings for major cities

Zillow is back with its 2014 rankings of “Best Cities for Trick or Treating.” San Francisco, Los Angeles, and Chicago round out the top three. The methodology has not changed much compared to 2013:

We take data seriously here at Zillow, even when it comes to trick or treating. While wealthier neighborhoods are often known for their frightfully sweet harvest on Halloween night, we calculate the Trick-or-Treat Index using a holistic approach with four equally weighted data variables: Zillow Home Value Index, population density, Walk Score® and local crime data from Relocation Essentials. Based on these variables, the index represents cities that will provide the most candy, in the least amount of time, with the fewest safety risks.

In the era of Internet lists, this is a potentially catchy list. The factor of housing values filters out a lot of places with the top 10 dominated by coastal cities with Chicago as the only Midwestern or Southern entry.

Yet, it also seems limited to major cities, not even metropolitan regions, so its scope is limited. Many Americans live in suburbs or smaller big cities and those don’t seem to make the cut here. Perhaps Zillow doesn’t have the same availability of data in these places.

I suspect that people within these cities would not all appreciate it if people took these rankings seriously and in large numbers flocked to the highest-rated neighborhoods just to get better candy more quickly. But, it would certainly be interesting if large numbers did show up…

Zillow starts estimating remodeling costs

Zillow is already known for estimating housing values but just last week they started offering another estimation: what it will cost to remodel.

On Tuesday, Zillow waded into the world of remodeling, by pairing its database of photos of pretty rooms (from its for-sale listings) with the tool that seems to drive most aspects of American life these days, the algorithm.

Thus, the company is attempting to answer the obvious question that dogs glossy magazine layouts and cable TV decorating shows: How much would it cost to do a room like that, anyway?

Remodeling costs are notoriously difficult to generalize about with the public, for a number of reasons…

Undeterred by all that, the website has rolled out Zillow Digs, which has launched with about 6,500 photos of kitchens and master baths. Beyond mere real estate eye candy, though, it also has brought in a team of contractors to offer estimates of the cost of each room’s appliances, finishing materials, labor, etc.

As the article notes, this could be quite a money maker with the number of Americans who remodel their homes. It seems like the algorithm could benefit from getting some data after the remodeling takes place; perhaps a later appraisal or an estimate based on a later sales price. Of course, this would require waiting some time after the remodeling takes place and perhaps there are not enough cases of remodeling within a certain geographic area to make a good estimate.

In the end, it will be interesting to see how many people make use of this new site. Additionally, how many will be willing to make financial decisions based on the estimates from the site?