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.
Compulsory voting
A study of a Swiss canton where compulsory voting was enforced found that compulsory voting significantly increased electoral support for leftist policy positions in referenda by up to 20 percentage points. Another study found that the effects of universal turnout in the United States would likely be small in national elections, but that universal turnout could matter in close elections, such as the presidential elections of 2000 and 2004. In the United States, Democrats would most likely fare better under universal voting (as nonvoters are generally more Democratic) but due to the dearth of close races in the United States, universal voting would change "very few election outcomes." Research on compulsory voting in Australia found that it increased the vote shares and seat shares of the Australian Labor Party by 7 to 10 percentage points and led to greater pension spending at the national level. While [weakly enforced] compulsory voting in Austria increased overall turnout by roughly 10 percentage points, there is "no evidence that this change in turnout affected government spending patterns (in levels or composition) or electoral outcomes." A 2016 study finds that compulsory voting reduces the gender gap in electoral engagement in several ways. A 2016 study of the Netherlands found that the abolition of compulsory voting increased the vote share of Dutch social democratic parties while reducing the vote share of "minor and extreme parties".