- Joined
- Jun 27, 2017
- Professional Status
- Certified General Appraiser
- State
- California
You don't understand the logic. However you want to breakdown the value composition of a comparable that sold for $X, then common sense is that all of your value contributions would add up to exactly $X. That is one constrain 99.9% of traditional appraisers bypass because they don't go through value contributions to calculate adjustments. That value contribution logic implies that when you calculate the feature adjustment as the difference between the feature value contribution for the subject minus the feature value contribution for a given comp, mathematical, all of the comparable adjusted sales values will be the same. That is because they are all adjusted to the same subject. It's just mathematics.It doesn't.
You have to remember that this is the person that massages his data to the point where EVERY comp adjusts out to exactly the same $1. Use comps that have a sales price listed generally to the $1,000 level and he likes to claim accuracy to the $1 level based on that data. Sad, clueless, but still funny.
The difficult part to understand beyond that is how we get the subject value, since that is what the whole purpose of the sales grid is.
1. We create a high quality model based on the measured features, e.g. GLA, Lot Size, Room Counts, garage size and so on. If you use MARS, and are experienced in using it, you should be able to get an R2 of around 80% and a CVR2 around 60%+. That leaves you with another 20% to explain with the unmeasured or subjective features like condition, quality of construction, functional vale, aesthetics, style, etc.. Now, using simple math again, the sum of those values is the actual net sale price minus the estimated value from the MARS model. That is your second constraint. You can break that "residual" amount down however you want and it won't impact the value conclusion. That breakdown has no impact on value it is just providing the report user the reasons it is what it is.
2. The one critical point of this kind of valuation is ESTIMATING the residual for the subject, since you don't have a net sale price of that. You do that by ranking the residuals of all the comps that went into the regression, say 150 comps, from largest to smallest. Generally, if you did a good job on creating the MARS model, the appeal of the comps willl correlate with the residual value. The most appealing comps will have the highest residual; that is to say buyers are willing to pay more than what size, age or location would otherwise indicate, because the properties are generally more appealing. If you go through this exercise, and look at the rankings, you will see the correlation. So, then, take your subject and rank it in the 150 comps by find the best comps to put it between. It doesn't have to be exact, but should be within +/- 10% of its ideal location. A 10% error on that remaining 20% is 2%. So, your estimate of the subjects residual is within +/-2%, generally. In fact, in many cases, it can be very clear that it is better than that. So, this method is actually very objective, verifiable and well within +/-2% accuracy.
This is really, from my point of view, rather simple. But it appears far beyond the mental capability of even the smartest MAIs. I guess it requires MENSA level intelligence. Shocking!
Anyway, it appears the WORLD is frigging tired up putting up with asinine appraisers and is going replace them with robots far sooner than expected.
So, why the fuss?
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