Electoral system
Electoral rules place limits on suffrage and candidacy. Most countries's electorates are characterised by universal suffrage, but there are differences on the age at which people are allowed to vote, with the youngest being 16 and the oldest 21 (although voters must be 25 to vote in Senate elections in Italy). People may be disenfranchised for a range of reasons, such as being a serving prisoner, being declared bankrupt, having committed certain crimes or being a serving member of the armed forces. Similar limits are placed on candidacy (also known as passive suffrage), and in many cases the age limit for candidates is higher than the voting age. A total of 21 countries have compulsory voting, although in some there is an upper age limit on enforcement of the law. Many countries also have the none of the above option on their ballot papers.
Voter registration in the United States
It has been argued that some registration requirements deter some people (especially disadvantaged people) from registering and therefore exercising their right to vote, resulting in a lower voter turnout. According to a 2012 study, 24% of the voting-eligible population in the United States are not registered to vote, equaling some 51 million U.S. citizens. While voters traditionally had to register at government offices by a certain period of time before an election, in the mid-1990s, the federal government made efforts to facilitate registering, in an attempt to increase turnout. The National Voter Registration Act of 1993 (the "Motor Voter" law) now requires state governments to "either" provide uniform opt-in registration services through drivers' license registration centers, disability centers, schools, libraries, and mail-in registration, "or" to allow Election Day voter registration, where voters can register at polling places immediately prior to voting. In 2016, Oregon became the first state to make voter registration fully automatic (opt-out) when issuing driver licenses and ID cards, since followed by four more states. Political parties and other organizations sometimes hold "voter registration drives", that is, events to register new voters.