Each year county assessors develop a new assessment and tax roll. From one year to the next, the major change between rolls is the property values. Change is the one constant in the value of real estate. Changes may be gradual and not easily noticed, or changes may occur rapidly in an active market. Because property values are always changing, assessors must update the real market values (RMV) to keep them current with the market. The process for measuring these changes is called the ratio study. The assessor is required to create a ratio study annually (ORS 309.200).
Both state and local county assessment agencies use ratio studies to monitor appraisal performance, determine the need for a general revaluation, establish priorities for revaluation of selected groups of properties, identify potential problems with appraisal procedures, conduct market analyses, and adjust appraised values between revaluations.
