Sales Ratio Definitions The Sales Ratio Study is a study used to measure the level of appraisal. By checking the level of appraisal and equalizing values of the Public Service Companies of 4th and 7th year counties, we are ensuring fairness and equality amongst all taxpayers. When reviewing this book, you will find the following columns: Revaluation Year, Median, Tax Rate, Effective Tax Rate and the COD (Coefficient of Dispersion). The list below gives an explanation of what each column represents. Revaluation Year This is the year of the last revaluation for the county identified in the same row. Median This column represents the final sales ratio value certified by the Department of Revenue. We calculate the median by aligning all of the ratios for a particular county from highest to lowest, and then selecting the middle value. If there is an odd number of values the median is the middle number, if there is an even number of values, the median is the two middle values added together and then divided by two. The median is chosen over other central tendencies such as the mean (average), because it is effected less by outliers. Tax Rate This is the actual tax rate of the current tax year. Effective Tax Rate The effective tax rate is the actual tax rate multiplied by the assessment level (median). Coefficient of Dispersion The Coefficient of Dispersion is used to measure uniformity in the sales ratio study. A high COD shows that there is a large variance between the highest ratios and the lowest ratios compared to the median. A low COD represents conformity amongst the county. In a reappraisal year, we would expect the COD to be lower than in non-reappraisal years.