this is something i got from forum a while back, cant remember who posted, maybe resguy; i now put it in all my reports
Not all adjustments in the Sales Comparison Approach can be directly extracted or supported by the available market data with a high degree of accuracy. Some adjustments have an element of subjectivity and professional judgment which the appraiser has applied based on prior observations of the reactions of typical/knowledgeable buyers' and sellers' in the marketplace. This method is a standard and well accepted practice within the appraisal industry. All interested parties are encouraged to have an understanding of basic valuation practices when appraising atypical or complex properties;or where there is an extreme absence of like elements of comparison; or in instances where the market data is inconsistent with which to draw better supported adjustments and overall value conclusions. Appraising Residential Properties, 4th Edition, Appraisal Institute, Page 342, "Limitations of Paired Data Analysis" states: "...This brief discussion of paired data analysis may seem to suggest that identifying the effects of property differences from market data is a straightforward procedure that can produce accurate, complete mathematical results in all appraisals. Such an impression would be misleading. Appraisers develop an opinion of market value by applying their judgment to the analysis and interpretation of data. Paired data analysis is a tool that an appraiser can apply to market data in some circumstances. When used in conjunction with other analytical tools, this type of analysis supports and guides the appraiser's judgment, but it does not take its place. Perfect sets of comparables that vary in a single, identifiable respect are rarely found. Because properties that are sufficiently similar to the subject are usually limited in number, the decision to apply paired data analysis in a given situation is a matter of judgment. Often the sampling size may not be larger enough to provide a solid statistical foundation for the appraiser's conclusions."