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5 | Page <br /> <br />Arithmetic Mean Ratio <br />The mean is the average ratio. Unlike the median, the mean is influenced by outliers. We use this <br />ratio not only to measure our assessment level, but also to analyze property values by <br />municipality, type of dwelling and value range. These studies enable us to track market trends in <br />neighborhoods, popular housing types and classes of property. <br /> <br />Within the county, we strive to achieve a ratio within the 93%-96% range for the median and <br />mean. This allows us a margin to account for a fluctuating market and still maintain ratios within <br />state mandated guidelines. <br /> <br />Coefficient of Dispersion (COD) <br />The COD is used to measure the accuracy of the assessment. The COD indicates the spread of the <br />ratios from the mean or median ratio. The goal of a good assessment is a COD of 10 to 20. A COD <br />under 10 is considered excellent and anything over 20 will result in an assessment review by the <br />Department of Revenue. <br /> <br />Price-Related Differential (PRD) <br />The PRD is used to measure value related inequities in the assessment, referred to as regressivity <br />or progressivity. Appraised values are regressive if high value properties are under appraised <br />relative to low value properties and progressive if high value properties are over appraised <br />relative to the low value properties. The PRD is found by taking the mean (average) ratio of the <br />sample and dividing it by the weighted (aggregate) mean ratio. The acceptable range is .98 to <br />1.03. <br />