One-person, one vote. The Equal Protection Clause of the Fourteenth Amendment to the United States Constitution has been interpreted by the United States Supreme Court to require the States to draw legislative districts so that each district is about the same size in population as the others. In a case decided in 1964, the U.S. Supreme Court stated that the "overriding objective must be the substantial equality of population among the various districts." (Reynolds v. Sims, 377 U.S. 533). This is known as the "one-person, one vote" rule.
The 10% variance rule. In a series of cases following the Reynolds case, the Supreme Court established a 10% threshold variance for legislative redistricting. That is, if a state makes all its districts within 10% of each other in population size then there is a presumption that such district passes muster under the one-person, one-vote rule. If the variance exceeds 10% then redistricting plan will be upheld only if the State shows that such a disparity is justified by extraordinary circumstances.
Determining the variance. The Courts have approved the use of a statistical measure called the overall range to determine whether a districting plan meets the population equality standard set out above. In Arkansas, the overall range will be determined as follows. First, the Board of Apportionment will determine the population limits for districts in Arkansas by dividing the number of seats in each house of the General Assembly into the total state population. (Total Population /35 senate seats, and Total Population/100 House Seats) The result is the average district size. After the plan is drawn, the total variance is determined by measuring the percentage difference in population between the largest population district and the average district, and the smallest population district and the average district, and then adding the percentage differences together. This is the overall range.
For example, in the 2001 redistricting of the State Senate, the Board divided 35 (total number of Senate seats) into 2,673,400 (the total population of Arkansas in the 2000 census) to arrive at the average district size of 76,383. After drawing the new districts, the largest Senate district had a population of 80,191 , or 4.99% more than the average district size. The smallest Senate district had a population of 72,699, or 4.82% less than the average district size. Adding 4.99 to 4.82 yields an overall range of 9.81.