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5 | P a g e <br /> <br />studies enable us to track market trends in neighborhoods, popular housing types and <br />classes of property. <br />Within the county, we strive to achieve a ratio within the 93%-96% range for the median <br />and mean. This allows us a margin to account for a fluctuating market and still maintain <br />ratios within state mandated guidelines. <br /> <br />Arithmetic Mean Ratio <br />The mean is the average ratio. Unlike the median, the mean is influenced by outliers. We use <br />this 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 <br />trends in neighborhoods, popular housing types and classes of property. <br /> <br />Coefficient of Dispersion (COD) <br />The COD is used to measure the accuracy of the assessment. The COD indicates the spread of <br />the ratios from the mean or median ratio. The goal of a good assessment is a COD of 10 to <br />20. A COD under 10 is considered excellent and anything over 20 will result in an assessment <br />review by the 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 <br />regressivity or progressivity. Appraised values are regressive if high value properties are <br />under appraised relative to low value properties and progressive if high value properties are <br />over appraised relative to the low value properties. The PRD is found by taking the mean <br />(average) ratio of the sample and dividing by the weighted (aggregate) mean ratio. The <br />acceptable range is .98 to 1.03. <br />