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How Accurate Are Zillow's Zestimates?
I recently attended a trade show where the two most popular questions at the Zillow booth were 1) Where do you get your data and 2) How accurate are your Zestimates?
Data -  We get data from a number of sources, but the most popular place is from county records.  In some counties this is great, in others (especially in non-disclosure states)  the data is very weak and we have to turn elsewhere.  Of particular note to Agents- we also get data from listing feeds.  Say the county said a home had 3  bedrooms, but when you post the listing on Zillow you say it has 4.  We will override he county data with your information, as we figure you are the more reliable source, and the Zestimate could change based on this.  If you want to read more about the Zestimate, please visit What's A Zestimate Value.
Accuracy  -  We constantly monitor how accurate the Zestimates are by comparing them to closed transaction data on the day the property sells.  By looking at the deltas that exist between the Zestimates and the sold prices, we can conclude our median err (or accuracy) rate.  We then publish these figures across all counties.  We ... more

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