A voter may deliberately spoil a vote, for example as a
protest vote, especially in
compulsory voting jurisdictions, to show disapproval of the candidates standing whilst still taking part in the electoral process. Protest votes have been associated with
nomination rules preventing a candidate from standing on the ballot, or low
political trust. Spoilt votes can be explained as a form of
strategic voting due to the violation of the
independence of irrelevant alternatives property of an
electoral system. A
None of the above option on the ballot was shown to reduce spoilt votes. The
Supreme Court of India mandated 2013 in India the "None of the above" option. The
validity of an election may be questioned if there is an unusually high proportion of spoilt votes. In multiple-vote U.S. ballots,
voter rolloff is calculated by subtracting the number of votes cast for a "down-ballot" office, such as mayor, from the number of votes cast for a "top-of-the-ballot" office, such as president. When the election jurisdiction does not report voter turnout, roll-off can be used as a proxy for residual votes. Some voters may only be interested in voting for the major offices, and not bother filling in the lower positions, resulting in a partially valid ballot. While it is not illegal to advocate informal voting in
Australian federal elections, it was briefly illegal to advise voters to fill out their ballots using duplicated numbers.
Albert Langer was jailed for violating an
injunction not to advocate incomplete preference voting for the
1996 Australian federal election. Despite the government criminalising inciting voters to cast invalid ballots or not vote, as well as attempts to boost voter turnout, the election recorded a record number of invalid ballots as well as historically low voter turnout. Intentionally spoiling someone else's ballot before or during tabulation is considered
electoral fraud. ==Unintentional spoiling==