Statistical Data

IAAO Standards

IAAO Standards

Sales Ratio Study- A ratio study that uses sale prices as proxies for market values.

Coefficient of Dispersion (COD) - The most used measure of appraisal uniformity. It is built on the average deviation, which measures the average absolute difference of the ratios from the median. The average deviation of a group of numbers from the median expressed as a percentage of the median. In ratio studies, the average percentage deviation from the median ratio. Low CODs (15.0 or less) tend to be associated with good appraisal uniformity.

Price-Related Differential (PRD) – The mean divided by the weighted mean. The statistic has a slight bias upward. Price-related differentials above 103% tend to indicate assessment regressivity; price-related differentials below 98% tend to indicate assessment progressivity.

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