They need to throw out one of this founding appraisal book. It has a comment about proving adjustments. Burn this witch's comments.
The Appraising Residential Properties, 4th Edition, Appraisal Institute, "Other Quantitative Adjustment Techniques”, Page 344 further states: “…In instances where paired sales analysis is not conclusive, the appraiser may apply judgment to resolve the problem." The adjustments resulting from the appraiser's judgment is based on a study and understanding of historic or past buyer preferences. It further suggests that cost and depreciated cost data may be used with the appraiser arriving at the value contribution (not cost new) of certain features. The process of supporting the contribution of individual variables (features) is limited and often difficult to quantify, with adjustment deemed to be qualitatively supported unless otherwise addressed. All methods of supporting adjustments are usually limited by inherent uncertainties within the applications themselves.
My final comment: Burn uad3 at the stake, it will be a false prophet of exact proven adjustments. Either that, or we will be burned. Soon USPAP will change the definition from opinion of value, to fact of value.