Explaining Changes to Zestimate History
By: David Gibbons, Zillow Director, Community Relations | January 15, 2008
Last week’s launch of our new Zestimate algorithm involved the most significant update to Zestimate values since Zillow launched in beta in early 2006. We also updated more than 10 years of historical Zestimate values. The changes made to the Zestimate history have raised quite a few questions so I thought it could be useful to explain what we did - and why.
When you click on “Zestimate and Charts” for a home on Zillow, you get Zestimate data and a chart that displays historical Zestimate values like the one pasted below. The dark blue line (labeled “This home”) shows the history of the Zestimate value for the home. The “30-day change” is the difference between the most recent Zestimate update and the Zestimate value that was published 30 days earlier (except for the next two weeks or so until we publish updated Zestimates again … which is the issue here.) “Last updated:” shows the date of the home’s last Zestimate update (we typically refresh Zestimates weekly; usually on a Thursday.)
The chart not only records historical Zestimate values; it is, more importantly, a useful indicator of the accuracy for that home’s Zestimate (compare the dark blue line to historical sales events) and it suggests the trend in each home’s value. Since our new algorithm significantly increased Zestimate accuracy, it was important to apply the new algorithm to a home’s Zestimate history to more accurately reflect that home’s value over time. By updating historical Zestimates, trends are now more accurate and we can tell whether the Zestimate value would have successfully predicted prior sales values. Both of those benefits far outweigh the convenience of knowing the Zestimate value that was published on any day last year and thus, it was important to refresh Zestimate history when we upgraded algorithms and said goodbye to “Beta”.
If you regularly check Zestimates, I understand that a change to Zestimate history can be confusing. And yes, the 30-day change isn’t (currently) relative to what was published in December; rather it’s relative to what the new algorithm would have published a month ago had it been launched then (still with me?). Within a couple weeks, the 30-day change will again reflect the movement from the currently published Zestimate. If your Zestimate history has changed significantly, check it out and let us know what you think - and I hope you’ll agree with our findings; that the accuracy of both Zestimates and Zestimate history are significantly improved.
- Stumble it!
- Categories: Zestimate, Zillow
Comments
21 Comments so far
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Dan Isaacs on January 18, 2008 11:14 am
Drew, it has been my observation over the last year or so that your historical values always changed month to month. At least, they always did for my house. Of the last 6 Zestimate changes in particular, none listed the delta accurately.
I posted a thread about this back in Nov. http://www.zillow.com/forum/site/ViewThread.htm?tid=10977
Have you not always applied the most recent set of data/algorithms to a homes historical zvalues?
Davis Hayden on January 18, 2008 7:36 pm
Ok, I need to find a way to contact zillow as you have made a major mistake in this new estimate. How does one get through to you? you have my email address, can you please send me an email that I can reply to. Thanks
Davis
splintair on January 23, 2008 2:57 am
your sat-pic is 2 years + old. we built over a year ago and the old building is still there and NO value. we would like to update, but cannot with out a new view and current value
Thank you.
Davis Hayden on January 23, 2008 4:17 pm
Ok, how does one contact you? Please send me an email or something. Thanks
David Gibbons on January 23, 2008 4:35 pm
Davis - I’ve forwarded your details to our support team who will be in touch shortly.
splintair - our satellite imaging partners are constantly updating their library; I’m sorry it’s been a while. Please also note that if the facts about your home are incorrect, your Zestimate value will not change unless you correct them and that the age of the aerial imagery has no impact on the accuracy of the Zestimate value.
splintair on January 23, 2008 8:17 pm
right back to the original comment—there IS no value….
David Gibbons on January 23, 2008 8:30 pm
splintair -
Got it. If there was a Zestimate but now there isn’t, please reply with the address so we can investigate further. If there simply never was a Zestimate on the home; my apologies - we’ve calculated estimates for 3/4 of the homes in the US so far and are working on the rest.
splintair on January 23, 2008 8:34 pm
previous house was there for 30 years and that went off propety in Nov 2006. replaced with a new house in april 2007. address is:
2625 Los Padillas Road, SW, Albuquerque, NM 87105-7248
Thank you.
Matt Oliverius on January 25, 2008 5:54 am
You have the wrong square footage on my house at 2518 97th PL SE, Everett, WA 98208. It is 1704 square feet. The difference is the LIVABLE space in the family room which is 3 steps down from the kitchen. It was finished when we bought the house as new construction and it is part of this TRI-LEVEL house. Please correct it, I have the drawings and the appraisal on the house to validate this information, and you have already fixed my neighbors square footage at 9609 25th Drive SE, Everett, 98208. Our house is the same style as our neighbor’s and the neighbor’s is only slightly larger in size. Thank you
Drew Meyers on January 25, 2008 8:39 am
Matt-
If you’d like to update the home facts for your home, please claim the house and then edit the facts. Once you do that, your updated facts will be used as an input to the zestimate formula next time we push zestimates to the live site again (currently, about once a week).
To claim your home, please go to your home details page, and click “claim your home” in the toolbox on the left.
Bo on January 25, 2008 9:59 am
Drew,
I notice that the comp set for my neighbor is wrong. Therefore brought the house value way down. My house is on Century Street in Moreno Valley, CA. I know that there was a house on Century that was sold for $583K which was not included in the comp set. There was another house recently sold for $630 which as not shown in the comp set also. But instead there were a number of smaller properties that sold for $300K - $400K that were used in the comp. This error brought the value in my neighborhood way down. Please make the correction. Thanks, Bo
andrew Tan on January 29, 2008 4:54 am
What happened to home prices in Honolulu, Hawaii. There’s a huge spike where prices went up by at least 2X, in some cases 4X, then a drop back down. Things are still way way way above normal though.
What’s up?
Dr. G.C. Corynen on February 4, 2008 6:07 pm
Please clarify more precisely what your algorithm does including the principles upon which it is based.
Also please explain in more technical terms how the new algorithm differs from the old one.
Thank you.
Pag on March 13, 2008 7:17 am
The purchase price is not included in my zestimate. I do not undersand the reason. We bought the house through a realtor, it was not a family transaction. I would like to know what the irregularity was. Can someone please email me so we can fix this?
Thank you.
David G from Zillow.com on March 27, 2008 8:25 pm
Pag - what’s your address?
splintair on March 28, 2008 5:55 am
OK, “claimed” my house and you now show it’s location. Now I have to wait for an updated aerial and county evaluation to catch up. 2625 Los Padillas Rd, SW, Albuquerque,NM 87105. Thank you.
pag on March 28, 2008 10:25 am
David-
The house is at 8 Old Musket lane zip 06877. I was just wondering why the purchase rice was not included in the zestimate.
Thanks
Pag
Deborah on February 4, 2009 5:39 pm
When does the actual sales price take effect on the value of the home? For instance, if it sold in Dec, when would I expect the change to reflect, as a sales price is best indication of value. When a property is listed, do you post the listing price as the estimate? Will it affect the estimated value? How long before a price reduction will it take to post the changed estimate?
Colleen Hicks on April 21, 2009 10:24 am
Hello,
We believe that the ZEstimate for our house
is very low because of incorrect sales data.
It says the following:
Sold 01/16/2003: $148,000
In reality the house only sold once, for
$ 142,500 on 3/13/1997. We are the original
owners. It never sold in 2003.
If possible, can you remove this information or
at least add “Transaction Not Included in Zestimate”? Our ZEstimate is low, and we believe
we are asking a fair price for our home (and
have updated the owner information on Zillow accordingly).
Thanks!
Michael Roy on May 21, 2009 5:26 pm
Hi David,
I like the idea of new Home Value Graph, however; mine is missing and is not there. Everything else is there, but the spot where the graph should be is blank.
The address is 14607 SE 170th Pl Renton WA 98058
Thanks
Lizabeth Glass on August 10, 2009 3:38 pm
I just got off the phone with one of your representatives. I am very upset. I am trying to get a loan modification. Since Zillow states it is worth $292,500 the bank states there is equity. There is no equity, I have lost a lot of money. The house next door & 2 doors down are on the market. $175,000 & $190,000 very similar in style/age/assessed value & of course location. I have changed Zillow’s information, however how is 500sqft going to make $100,000 difference. I am also an appraiser, this concerns me that banks are using this site for a market analysis. This site changes people’s lifes! Please change mine by assuring me this will be updated. By the way, those two houses still have not sold, this area has declined considerably. Why would someone buy an old house when they can buy a new one down the street with 1000 more square feet for $250,000. Please be courteous and correct the data. My assessed value is $226,200, neighbor #1 $220,800 #2 $242,500. Your zestimate $292,500, $207,000 & $190,000 in that order. My address: 1904 3rd st, Marysville, WA 98270, #1 neighbor 1908 3rd St, #2 1912 3rd St. I purchased for $220,000 in 2002 - your represtative stated that is why mine is higher than the neighbor who purchased theirs for $185,350 in 2004 - please tell me this is not how you are conducting business. He could not answer any of my questions. He simply said to go into the site & change my property details. How is 500 sq ft make $100,000 difference.