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Zestimates are worse than random. There seems to be no sanity-checks in the algo whatsoever.

Check out this Baltimore home. In a single month it's estimate went from $700k to $300k, then back to over $700k during the worst part of the housing slump, and back down to $300k during the recovery. lol wut?

http://weblogs.baltimoresun.com/business/realestate/blog/Zil...

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I did an analysis on the accurate of Zestimates a few years ago. I took sales data for my county from the previous month (that Zillow had not imported yet) and compared it to the Zestimates Zillow computed. The mean error was almost 0, but the standard deviation was about 20%. An engineer from Zillow wrote to me and said my analysis was close to their own internal measurements. Their algorithms might have improved since then since it sounded like it was something they were continuously trying to improve.

do you have a link to that analysis?

It was on my old blog which is no longer online. I'll see if I can find the article in my backups and post it somewhere. I should probably do the analysis again since my original test was during the end of the housing bubble when prices were unstable.

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