Large changes in an AVM or RVM estimate (Estimated Home Value) can be attributed to lacking or lagging public records data. For example, a property may have no or few accurate comps. If such comps become available, the property’s AVM estimate could significantly increase or decrease in short order. RPR also made an improvement to AVM data in May 2010 that has resulted in significant changes in some cases since that time.
In addition, properties can shift from having an AVM estimate to having an RVM estimate. This, too, can cause increases or decreases in the estimate because an RVM is considered the more accurate estimate, drawing upon licensed MLS listing data in addition to public records data. Often it can take a month or two following the transition to an RVM estimate for the property's estimate history to not seem erratic. You can review a property's estimated value on the Sales and Financing History chart (History tab of the Property Details page), mousing along the trend line, to see if the estimate changed from an AVM to an RVM.
Occasionally you will see significant fluctuations for an area reflected in its Median Estimated Home Value chart. This can happen when an area's home value estimates are based on RVM estimates, and the RVMs are unavailable for a particular month. When this happens, AVMs are used to calculate the median instead, and the substitution can create a significant variation in the median pattern.