Originally posted by @Michael Buttram:
I was definitely planning on relying on actual sold transaction data -- are these values not reliable through Zillow and other sites? I knew that actual property listings are oftentimes dated versus the MLS.
Data quality is often an issue especially when information is passing through multiple intermediaries. It may get 'corrupted'. Here are some links that may describe some of these issues:
http://seattlebubble.com/blog/2013/09/16/zillow-trulia-still-apathetic-about-data-quality/
If you were also relying on any type of zillow estimate or anything that in some way relied on or utilized the 'zestimate', then that really might be a problem as anything with a 'zestimate' in it is often not only way off in some cases, they often literally revise the algorithm which does often mean revising their historical estimated data.
http://blog.louisgray.com/2011/06/zillow-rewrites-home-price-history.html
Zillows response on this is also somewhat of concern:
This is directly from Zillow:
Do you ever change prior Zestimates?
Yes. When major improvements to the algorithm are made, we do re-compute the historical Zestimates for affected homes. Our purpose in doing so is to provide consumers with the best estimate of historical property valuations. A historical Zestimate is not like a historical stock price, which doesn't change after being recorded. A stock price is a record of an actual empirical event (and, as such, shouldn't change). A Zestimate, on the other hand, is an estimate of the market value of a home, and can change when we have a better algorithm to estimate that value....
Does the Zestimate algorithm ever change?
Yes, a team of statisticians is working every day to make the Zestimate more accurate....