Youth vote in the United States
The youth vote in the United States is a political term used to describe 18- to 24-year-olds and their voting habits. Many policy areas specifically affect the youth of the United States, such as education issues and the juvenile justice system. The general trend in voter turnout for American elections has been decreasing for all age groups, but "young people's participation has taken the biggest nosedive". This low youth turnout is part of the generational trend of voting activity. Young people have the lowest turnout, though as the individual ages, turnout increases to a peak at the age of 50 and then falls again. 
Ever since 18-year-olds were given the right to vote in 1972, youth have been under represented at the polls. In 1976, one of the first elections in which 18-year-olds were able to vote, 18-24 year-olds made up 18 percent of all eligible voters in America, but only 13 percent actually voted - an under-representation of one-third. In the next election in 1978, youth were under-represented by 50 percent. "Seven out of ten young people…did not vote in the 1996 presidential election… 20 percent below the general turnout". In 1998, out of the 13 percent of eligible youth voters in America, only five percent voted. During the competitive presidential race of 2000, 36 percent of youth turned out to vote and in 2004, the "banner year in the history of youth voting," 47 percent of the American youth voted. Recently, in the 2008 U.S. Presidential election, the number of youth voters tripled and even quadrupled in some states compared to the 2004 elections.
Voter turnout
For the denominator, it is often assumed that the number of eligible voters was well defined, but again, this is not the case. In the United States, for example, there is no accurate registry of exactly who is eligible to vote, since only about 70–75% of people choose to register themselves. Thus, turnout has to be calculated based on population estimates. Some political scientists have argued that these measures do not properly account for the large number of illegal aliens, disenfranchised felons and persons who are considered 'mentally incompetent' in the United States, and that American voter turnout is higher than is normally reported. Professor Michael P. McDonald constructed an estimation of the turnout against the 'voting eligible population' (VEP), instead of the 'voting age population' (VAP). For the American presidential elections of 2004, turnout could then be expressed as 60.32% of VEP, rather than 55.27% of VAP.