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Replies (7)
- Pasadenan
- Contributions:21466
They did it before (January 2008) and they will do it again.
They are constantly seeking additional information on the housing units, and better ways to track the housing market trends. When they have better methods and better data to improve the tolerance range, they not only recalculate the present, but also the past, to make sure one is viewing the market trends and not changes in estimating methods.
The present recalculation only went back to 2006. They have already posted they are still doing some additional tweaking, and that they will be recalculating at least back to 2001, possibly back to 1997.
Yes, I'm sure you must still be using an abacus and a slide rule and have not tried using a computer nor a program like excel yet.
(By the way, I knew it was coming, so I saved the "gif" images for each of the 1yr, 5yr, and 10yr trend charts for each of the properties I was tracking a couple months ago). (You get to the GIF images by using the "print" button on the home details page, and escaping out of the print, then right clicking on the chart image and selecting "open in new window", and then adjusting the time frame and the curves you want shown in the URL parameters in the address box).
They are constantly seeking additional information on the housing units, and better ways to track the housing market trends. When they have better methods and better data to improve the tolerance range, they not only recalculate the present, but also the past, to make sure one is viewing the market trends and not changes in estimating methods.
The present recalculation only went back to 2006. They have already posted they are still doing some additional tweaking, and that they will be recalculating at least back to 2001, possibly back to 1997.
Yes, I'm sure you must still be using an abacus and a slide rule and have not tried using a computer nor a program like excel yet.
(By the way, I knew it was coming, so I saved the "gif" images for each of the 1yr, 5yr, and 10yr trend charts for each of the properties I was tracking a couple months ago). (You get to the GIF images by using the "print" button on the home details page, and escaping out of the print, then right clicking on the chart image and selecting "open in new window", and then adjusting the time frame and the curves you want shown in the URL parameters in the address box).
- Pasadenan
- Contributions:21466
By the way, there was a thread on Zillow's use of Amazon Cloud Computing that referenced a 2008 Forbes Article that talked about the last time Zillow did a massive recalculation.
Where can I find more info. on Zillow's use of Amazon Web Services cloud?
Don't forget this is "the internet", not a published print book. (And even print books get reprinted with major revisions). If you need historical "web site" information, you need to archive it, as many archiving companies already do.
Where can I find more info. on Zillow's use of Amazon Web Services cloud?
Don't forget this is "the internet", not a published print book. (And even print books get reprinted with major revisions). If you need historical "web site" information, you need to archive it, as many archiving companies already do.
- Dunes....
- Contributions:3894
"Since so much of Zillow's mission is about increasing the transparency of data in the real estate market, we apply this same rule to our own data and, by doing so, help consumers and professionals better understand the performance of our models across all geographies."
"Historical Zestimates"
"With the data delivery yesterday, we have re-computed historical Zestimates back to January 2006. There are a few algorithmic developments that we are still working on and, once these are done, we intend to re-compute all Zestimates back to 1996."http://www.zillow.com/blog/research/2011/06/14/upgrading-the-zestimate/
So what do you think Mozeu?..
- mpzm
- Contributions:11
Prior to the change, Zillow claimed a high rate of accuracy in my county. Yet with the modified algorithm, prices have changed by 10% or more. So...apparently, the old estimates were not as accurate as had been previously claimed? Zillow estimates should not be taken seriously!
- Pasadenan
- Contributions:21466
Well, with that kind of "logic", one should not take a CMA by a Realtor® seriously either as many of them differ by 30% or more from one another for the same property.
A house is only worth what a buyer will pay at that time, and what a lender will use to base a loan qualification on.
If you need a value for financing, you will need to pay for an appraisal, there is no way around it. If you need the value for tax purposes, you will also need an appraisal by a licensed appraiser in the area. Neither a Zestimate nor a CMA will satisfy as a substitute.
Besides, the previous claim was that the median difference between the "sold" prices and the "Zestimate" value for all Zestimated properties in the nation was 12.7%. And now the median difference between the "sold" prices and the "Zestimate" value is only 8.5%. The median difference states nothing about an individual Zestimate.
It helps to know what numbers you are talking about for correct interpretation before complaining about them.
Zillow publishes the median difference for 668 counties in the U.S. out of 2997 counties they calculate Zestimates for, out of 3135 counties they have home details pages for.
Data Coverage/Zestimate Accuracy
(Use the "download excel spreadsheet" to get county specific aggregate statistics).
A house is only worth what a buyer will pay at that time, and what a lender will use to base a loan qualification on.
If you need a value for financing, you will need to pay for an appraisal, there is no way around it. If you need the value for tax purposes, you will also need an appraisal by a licensed appraiser in the area. Neither a Zestimate nor a CMA will satisfy as a substitute.
Besides, the previous claim was that the median difference between the "sold" prices and the "Zestimate" value for all Zestimated properties in the nation was 12.7%. And now the median difference between the "sold" prices and the "Zestimate" value is only 8.5%. The median difference states nothing about an individual Zestimate.
It helps to know what numbers you are talking about for correct interpretation before complaining about them.
Zillow publishes the median difference for 668 counties in the U.S. out of 2997 counties they calculate Zestimates for, out of 3135 counties they have home details pages for.
Data Coverage/Zestimate Accuracy
(Use the "download excel spreadsheet" to get county specific aggregate statistics).
- mpzm
- Contributions:11
From a limited review of the market I know best -- the one in which I live -- Zillow's current and historical values appear to be considerably less accurate than they were before the algorithm change.
- MoZeu
- Contributions:4
It doesn't say much for Zillow's algorithms if they are that open to retrospective adjustment. In any event, in our neighborhood, if you look at trend charts for any house that has sold in the last 5 years or so, Zillow's adjusted estimates currently indicate that every single sale was about 5% over market value. Well . . . if every single sale is 5% over market value, I think that means that someone's estimate of market value at the time must be about 5% too low. Zillow has homes on my street now valued at about $160 per square foot. That has never been true, is not currently and likely never will be true. So the changes to estimates that their algorithm has wrought are clearly not an improvement in accuracy in every case.
Retrospective Zestimates - massive changes!
I have seen a lot of ups and downs in our Zestimate over the four years that we've owned the house, but only ONGOING ups and downs. Not changes to data that was had been published. Unfortunately, I never saved screen shots of prior Zestimates, although I suppose I have some e-mails. This is just bizarre.
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