Data categories are divided into two types:
General data are collected on an area or region. It is appropriate for many properties. General data should be collected on all of the four forces that affect value.
Specific data are data that is specific to the property being appraised (the subject property) and the comparable sales used in its analysis.
Data sources are divided into two categories:
Secondary data are compiled by someone other than the appraiser. Examples include MLS, published sales data services, chamber of commerce, etc.
Primary data are data collected by the appraiser personally. Examples include a sketch of the structure based on building measurements, photographs of the property, sales information procured directly by the appraiser.