Instructions: The appraiser must use the information required on this form as the basis for his/her conclusions, and must provide support for those conclusions, regarding housing trends and overall market conditions as reported in the Neighborhood section of the appraisal report form. The appraiser must fill in all the information to the extent it is available and reliable and must provide analysis as indicated below. If any required data is unavailable or is considered unreliable, the appraiser must provide an explanation. It is recognized that not all data sources will be able to provide data for the shaded areas below; if it is available, however, the appraiser must include the data in the analysis. If data sources provide the required information as an average instead of the median, the appraiser should report the available figure and identify it as an average. Sales and listings must be properties that compete with the subject property, determined by applying the criteria that would be used by a prospective buyer of the subject property. The appraiser must explain any anomalies in the data, such as seasonal markets, new construction, foreclosures, etc.
The above instructions would be true whether or not the appraiser used an MC form. But note above, because teh data is reported in the neighborhood section , does not mean the data is all the sales or an average of salesw in the neighborhood !! The data are, see above, properties that compete with our subject property. That is what fannie wants to see on the trend line who cares what 1000 sf houses are doing if your subject is a 6000 sf luxury home?
An appraiser can provide additional broader market data or contrast broader market to subject property and competitive comp property trends, but not use it for the trends in neighborhood section.
PS if there were no forms and no fannie, this is just common sense and ethical appraisal practice. If I report the increasing prices and 60 DOM trend of 1000 sf starter home for my 6000 sf luxyr subject, when the subject competition shows stable or decling prices and 10-12 months DOM, I provided misleading results
Too much data can be as bad as not enough data, if the wrong data is relied on rather than the relevant data.
There may be scarce "data" for or subject but an appraisal is not about "data" it is about the analysis of that data. And we don't just analyze data, we analyze information yielded from data.. You only have 3 listings for jumbo house but all three of them are lower price than the sales and on the market over a year- you have enough data because it was enough to provide the information about the listing trend.