Austin
I understand the point you are making about the value being based on historical data and that it does not look forward beyond the effective date of the appraisal. However, if you are using historical data that "looks forward" to a current effective date, and you have missed an upward trend which is presently occuring, you can understate "market value". The key issue is how big an upward movement and how dated are your comps.
However, the primary thrust of my comments was to the issue of the variance in value.
We agree on this issue as I also believe that, in my market at least, there is easily over 10% of market variance in homes over $200,000, and as the homes get pricier, the variance gets larger. Even in cookie cutter type homes of $100,000, the variance is seldom less than 8%.
Stated differently, assuming that two appraisers are blessed with reasonably good data, and make the same basic assumptions regarding the property, there is nothing wrong with there being two differing value opinions regarding the most probable price.
As you suggest, you can graph the price of 30 sales and see the trend, as a staight linear regression. This would show a general range before adjustments. In the case cited by Quark, the subject would be at or near the upper end of the variance, perhaps even outside this range. But as you know, this is not the entire picture. It is not until you see the price line, adjusted for all factors which impact value, do you get the real picture.
I agree that selecting three sales (judgmental sample selection) and then adjusting is not very good as a statistical analytical tool. In fact, it is only as good as an individuals judgement as to what may or may not be an appropriate sale and is further compromised by the judgement as what factors impacting value.
But the same problem exists in more empirical statitical analysis methods, including multiple linear regression modeling. The key problem is identifying all those issue which impact value and having the statistical model treat them equally, ie, purely empirical statistical models that sample all data (or random data) within a population have difficulty with properly measuring more subjective issues such as design and appeal, condition, effective age and location. If it were not so, AVMs would work all the time. In fact, I have heard it said that pure empirical multiple linear regression analysis can only accurately account for 60% of the value factors.
I know you would argue that statistically such items have relatively high variance with little statical relevance, as opposed to GLA which has the opposite general attributes. You can then conclude that they should not truly be considered in the adjustments. But appraisers, brokers, buyers and sellers know these issue impact marketability and sales price. So the real question is how do you consistently statistically measure such issues.
I say that it is in the reconciliation of these issues that requires our professional judgment. Since each appraiser brings a unique set of "beliefs and opinions" regarding these issues, it is not surprising that we have a widely disparate views on how to treat them and their impact on value.
Hence, I do not find it hard to accept legitimate value ranges well outside the statitical range of variance, particularly if a given appraiser can cite examples in general support of his opinions. By the same token, if several appraisers are speaking on the same page, they should also be able to conclude independent opinions within the range.
Which method is correct? I do not know. My cut is that so long as an appraiser understands the concepts and can defend his position (not prove but support it) he/she has done the job as required by USPAP.
I also think, and I am sure you agree, that any appraiser who is doing his work by only using three comps, and not using statitical analysis to periodically validate his judgement on the most basic issues which can consistently be measured (such as GLA), is not moving forward in this profession but is falling behind.
Regards
Tom Hildebrandt GAA