Aggregate vs. Detailed Data - Zillow.com

According to Zillow.com, the home I purchased last fall has increased by 70% in less than a year:

While I wish that was so, I have a hunch that any real estate agent I talked to would collapse if I suggested listing the property for what Zillow suggests.

There are two upward spikes in the green line on the graph that represents what Zillow has thought my home was worth over the past decade.

The first, a year ago, is when I purchased the house for WAY more than Zillow said it was worth at the time.

The second is when Zillow decided that the house was worth WAY more than I paid for it.

So which is it?

Neither.

But, if you look at a large enough set of data, Zillow's numbers are probably pretty good. Notice the trend of the Yellow line. That represents the median price of homes in Minneapolis, Minnesota.

But here's the problem: I already know that my home is a bit above average if you take the entire city into consideration. You don't need to show me a graph to explain that concept to me. What I care about is my OWN house, and I know that data is broken.

So what exactly is the value of this data beyond inspiration for a blog post?

I've heard over and over how Zillow's data is skewed, but I don't think I've seen that much of a jump in an estimation. I mean, it would be nice if my home jumped 70% in a year. It seems that Zillow's AVM is trying to play catch up after your sold price was entered in.

Teresa, I think you're right about county data. In the case of my property, it hadn't changed hands in around 30 years, so they probably didn't have any county data to work with. But that didn't stop them from putting a price on my home.

Zillow was in the ballpark post-purchase until they decide to dramatically spike things up.

Brett, thanks for stopping by. Here's a link to a screenshot of my property's value on your site. It looks like Cyberhome's was equally wrong pre-purchase but is in what I'd consider to be the ballpark now (down ~4% since purchase).

Comments

1. Posted by: Teresa Boardman on September 28, 2008 9:30 AM:

There is a reason for the increase in the value of your home. Zillow gets the data from the county tax records that did not keep up with the times when it comes to value. You bought the home, the price was recorded at the county. Zillow grabs that data and your home instantly goes up in price. I am always amazed that companies like zillow can put data out there without showing the sources or the math and smart people see the data and think that it has merit. I have been tracking zillow home values and actual sale prices and have been tracking tax value and actual home sale prices. I am finding the strongest correlation between the zillow data and the county data.

Required fields marked with: *
Name*:

Email Address*:

URL:
Remember personal info?

Comments*:

HTML Tags you can use in your posts:
<b>Bold</b> = Bold
<i>Italicized</i> = Italicized
<a href="http://www.othersite.com">Link to Other Site</a> = Link to Other Site

Please keep comments on-topic. Contact authors or other commenters
directly for off-topic conversations.

Notify me of future comments via e-mail

Technology Evangelist Digest - Free Newsletter

Sign up for the free Technology Evangelist Digest to receive daily updates, editorials, and practical advice on emerging technology trends in hardware, software, webware, marketing and beyond.

Technology Evangelist Digest will keep you up to date on the technology trends that will help make you more productive and efficient both in business and your personal life.

Let's face it: If you made it to this line, you must have found something valuable on this page, right? Think about how cool it would be to have something free and interesting to read every day from Technology Evangelist by signing up today.

1. Fill in your email below,
2. Then click on the confirmation email you receive.
3. That's it. Your first Technology Evangelist Digest will arrive within 24 hours.