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dispersion (COD). Acceptable levels for COD depend upon the type of properties being reviewed. According to the IAAO, a COD should typically be less than 20%. Another statistical measure used to gauge assessment uniformity is the Price -Related Differential (PRD). The PRD tests vertical equity in assessments of higher valued and lower valued properties and indicates if all properties are assessed at the same level. Said differently, it measures progressivity and regressivity. PRDs should range between 0.98 and 1.03, except for very small samples. A PRD above 1.03 indicates under valuation of high priced properties, whereas a PRD below 0.98 shows over valuation of high priced properties. RATIO STUDY STANDARDS The IAAO is a professional organization of assessing officials that provides educational programs, assessment administration standards and research on assessment and tax policy issues. It has developed numerous standards and texts on assessment and assessment administration. Additionally, the organization is a founding member of the National Appraisal Foundation that developed the Uniform Standards of Professional Appraisal Practice (USPAP). Standards established by the IAAO are advisory in nature and provide guidance to those performing ratio studies in the mass appraisal field regarding the design, statistics, performance measures and related issues in conducting ratio studies. The Division uses fundamental ratio statistical measures of the IAAO standards, and it is guided by the criteria of the IAAO's Assessment Ratio Performance Standards to judge the performance of Lee County's assessments. See Table 1 below. Table 1: IAAO's Ratio Study Performance Standards 11 Measure of Price -Related Type of Property Central Coefficient of Differential Tendency Dispersion Single -Family Residential Newer, homogeneous areas .90-1.10 5.0-10.0 .98-1.03 Older, heterogeneous areas .90-1.10 5.0-15.0 .98-1.03 Rural residential and seasonal .90-1.10 5.0-20.0 .98-1.03 Income Producing Properties Larger, urban jurisdictions .90-1.10 5.0-15.0 .98-1.03 Smaller, rural jurisdictions .90-1.10 5.0-20.0 .98-1.03 Vacant Land .90-1.10 5.0-25.0 .98-1.03 Varies with local Other Real and Personal Property .90-1.10 conditions .98-1.03 11