In the absence of more reliable data regarding African–American voting strength, courts employ the general guideline that African–Americans must comprise 65% of a district's total population to control the electoral outcome in that district.
See Ketchum, 740 F.2d at 1415 (guideline used where empirical data ambiguous or indeterminate). This “rule of thumb” implicitly acknowledges that certain factors impact African–American voting strength disproportionately to white voting strength.
See Barnett, 141 F.3d at 702. For example, African–Americans tend to have higher non-voting age population percentages, lower voter registration, and lower turnout rates than whites.
Id. Accordingly, African–Americans “must have something more than a mere majority even of voting age population in order to have a reasonable opportunity to elect a representative of their choice.”
Ketchum, 740 F.2d at 1413. Courts have arrived at a 65% figure by beginning with a simple majority (50% plus one voter) and adjusting that figure upward by 5% to account for a younger population, 5% for low voter registration, and 5% for low voter turnout.
See id. at 1415. This incremental 15% adjustment is merely an approximate corrective, used to evaluate minority voting strength when more specific voting data (e.g., VAP, registration, and turnout) is unavailable.
See id. at 1413.