How is the voting-age population (VAP) constructed?
The voting-age population (VAP) estimates are generated from the July 1 Census Bureau population estimates by age-sex-race. Estimates for an election month are constructed by linearly interpolating the change between the most approximate pair of estimates. For example, to estimate the November, 2004 VAP population, add to the July 1, 2004 estimate the following: the July 1, 2004 estimate minus the July 1, 2003 estimate, divide by 12, and then multiply by 4. A similar linear extrapolation is used when projecting forward from the last available population estimate.
VAP population estimates are based on estimates of population change since the last census closely followed by the population estimates division at the Census Bureau. When a new census is conducted at the end of a decade, the population estimates are inevitably out of line with the actual census. The Census Bureau adjusts the previous decade's population estimates to conform with the new information revealed by the census. This is called the intercensal adjustment. Thus, we will not have a definitive estimate of the voting-age population and, by association, turnout rates in current decade's elections until the intercensal adjustment is released sometime after the end of this decade. In the meantime, the population estimates serve as the best estimate of the voting-age population of the United States.
Population estimates are available from the Census Bureau's website.
Although the VAP estimates presented on this website are based on official Census Bureau reports but they are not directly produced by the Census Bureau and -should not be cited as a Census Bureau product.