Why should I care if turnout rates are calculated as percentage of VAP or VEP?
There are two primary reasons why the voting-eligible population (VEP) is the preferred turnout rate denominator over the voting-age population (VAP).
- The most valid turnout rates over time and across states are calculated using voting-eligible population.
Declining turnout rates, post-1971, are entirely explained
by the increase in the ineligible population. In 1972, the
non-citizen population of the United States was less than 2 percent of
VAP and in 2004 it was nearly 8.5 percent of VAP. The percent of
non-felons among the VAP have increased from .5 to about 1 percent of
the VAP since the mid-1980s.
Using VEP turnout rates, recent presidential elections have
returned to their levels during the high participation period in the
1950s and 1960s.
- State turnout rates are not comparable using VAP since the
ineligible population is not uniformly distributed across the United
States. For example, nearly 20 percent of California's voting-age
population is ineligible to vote because they are felons or are not citizens.
There is a use for VAP turnout rates, which is why I provide them alongside VEP turnout rates.
- Some polling firms' survey universes are the voting-age population. These polling firms may wish to weight their surveys to their estimates of what the VAP turnout rate will be in an upcoming election, based on previous elections.