A single factor is rarely a complete indicator of sales opportunity. Regional drug sales are also influenced
by per capita income and the number of physicians per 10,000 people. Thus, it makes sense
to develop a multiple-factor index and assign each factor a specific weight. Suppose Virginia has
2.00 percent of U.S. disposable personal income, 1.96 percent of U.S. retail sales, and 2.28 percent of
U.S. population, and the respective weights are 0.5, 0.3, and 0.2. The buying-power index for Virginia
is then 2.04 [0.5(2.00) 0.3(1.96) 0.2(2.28)]. Thus 2.04 percent of the nation’s drug sales (not
2.28 percent) might be expected to take place in Virginia.