(a) As used in this chapter, the following terms are defined as follows:
(1) “Assessment ratio study” means the process of comparing, on a sampling basis, the current market values of properties to their assessed valuations, and of applying statistical procedures to determine assessment levels and to measure the nonuniformity of assessments.
(2) “Department” means the department of revenue.
(3) “Russell index of inequality” is that percentage obtained from the relation between the average absolute deviation of assessment ratios and the average ratio of assessment, and formulated as follows:
(b) Average absolute deviation of assessment ratios divided by the average assessment ratio = Russell index of inequality.