Can a single 2 sales data set, as your example shows, truly provide supportable $/GLA adjustment????
How about instead of.... House A traded for $100k. It is 1000 SF and dated. House B traded for $140k. It is 1200 SF and renovated. Solve for the difference in GLA.
We have this instead....House A traded for $100k. It is 1000 SF and dated. House B traded for $140k. It is 915 SF and renovated. Solve for the difference in GLA.
Speaking to all peers here...
Well hey, if you are willing to ignore the fact you need isolative data to extract an adjustment using matched pairs, it all works out just fine. Just ask J how to do it if you need advice.
There are something like 26 possible adjustments on a 1004 sales grid. Without getting too nit-picky here, that equates to 52 comparable sales to do matched pairs. Each of these sales would need to be paired (26) and each of those would need to be identical, except for the one feature, and each would need to represent the 26 different features. And all of that, is to produce just 1 data point for each feature. Anyone care to calculate the odds of acquiring the data? How about if you would prefer to have more than just 1 data point? I have more faith in winning the Powerball. The expectation, that dollar adjustments can be extracted, in a manner that is credible AND in a manner that can be supported, and when I say supported I mean in the sense you could present it on paper, which is the likely expectation of mortgage clients (certainly the expectation of the AMC the OP is dealing with here), is unrealistic. If matched pairs is considered the preferred and best method, what does that say about the other methods? Not all appraisal problems can be solved.
That said, IMO, adjustments we make on a regular basis are often/usually market-based and credible. How can I make such a claim after the previous paragraph? Because we analyze the trends in market data every day, for years on end. I don't know about the rest of you, but when I do an appraisal, I start with all sales in a market, not just the ones comparable to my subject. I ask the age old question as I go through them, why do some properties command more and why do some properties command less? I see patterns emerge and I can see changes in price points along the way. From there I isolate the properties competitive to my subject and go through them the same way I went through the entire market, asking why properties might sell for more or less, identifying trends. I call this method a trends analysis and it is from this, that I base my adjustments. Is it perfect? Nope. Can I prove the dollar amounts specifically? Nope. Is it credible and based on an analysis of market data? I happen to think so and yes. Would it fly with a mortgage client or state board? Maybe, maybe not. However, USPAP has a provision that states we must be ready to defend our actions or inactions that may appear to others to be wrong (paraphrase). I would rather explain why I did it this way, than explain why I did it in a manner that has more holes than Swiss cheese. Its easier to prove how the "recognized" methods are not credible, than it is to prove how they are credible. So, I punt. Maybe we might eventually all "recognize" these sorts of things.
Others have stated the "bracket method" is a good one. I tend to agree with that, so long as we are only talking about over-all general value, all features considered. Whoever decided that bracketing all features on a sales grid somehow provides support for the specific adjustment, fails to understand the math and method. It aint rocket science.
Speaking of rocket science, I did an appraisal for a real-life rocket scientist a while back. It was an estate, so I was free to talk about the appraisal. He wondered how we did it. He simply couldn't figure out how we could derive adjustments in the specific manner we do, considering the quantity of data available and the influences that affect the data (human nature issues). He said he would pull his hair out if tasked with what we do. So I explained it to him and was honest about it. He thanked me for being honest and then started telling me about the other appraiser he had hired (he was smart enough to get two opinions). The other appraiser filled him up with the usual BS, the sort you can find posted all over this forum, and he was not impressed, at least in a good way. Public trust is not only important, its the entire purpose of USPAP. Give that a think the next time you want to concoct a story of how you "credibly" extracted those adjustments.
I wonder how the tunes would change if we really were put to the test, such as submitting our work files that supposedly contain the data and math, rather than offering a written "summary" in the report. LOL. But our lender-clients don't want that my friends, they would prefer we were accomplices. Careful now.
Again, this is an example of how a single voice could help our profession.