Tennessee Code Title 67. Taxes and Licenses § 67-5-1605

(b)(1) In order to assist the board in its determination, the division of property assessments shall conduct appraisal ratio studies in all counties of the state at least every two (2) years unless otherwise determined by the board.

(2) Such studies shall determine applicable ratios by dividing the appraised values of property as shown on the official assessment records by the qualified selling prices of such properties.

(3) If a sufficient number of qualified sales do not exist for a subclass of property in a jurisdiction, appraisals of representative properties in that subclass may be used to supplement any existing sales in determining the ratios required by this section and § 67-5-1606.

(4) These appraisal ratio studies and any other pertinent information which may be available shall be used by the board to determine whether or not the property in each county has been assessed by the assessor of property as required by the constitution and laws of the state.

(5) Indexes to be used for revaluation shall be developed separately for each subclass of property based upon acceptable sales or appraisal data of representative properties in the subclass, or upon other relevant data. Multiple indexes within a subclass shall be developed as appropriate to recognize differential rates of change in values of property based on location, type of use, or other appropriate basis. A minimum sample size of one hundred (100) acceptable sales shall be used if available, otherwise all acceptable sales shall be used.