In the study of electoral systems, a wasted vote may be defined in two different ways:
The first definition includes only those votes which are for losing candidates (individual or party). The second definition is wider as it also includes surplus votes for winning candidates who would have won anyway without the wasted vote.
An electoral system which reduces the number of wasted votes can be considered desirable on grounds of fairness or on the more pragmatic basis that a voter who feels their vote has made no difference may feel detached from their government or lose confidence in the democratic process. The term "wasted vote" is especially used by advocates of systems like the single transferable vote, or instant-runoff voting which purport to reduce the numbers of such votes.
The term may be considered pejorative by opponents of such systems. Their arguments may either suggest that in any voting system each vote is wasted (unless the result is decided by a single vote), or that no vote is wasted as each one sends a political signal which will be taken into account in preparation for the subsequent election.
In election campaigns, a leading candidate may appeal to voters who support a less-popular candidate to vote instead for the leading candidate for tactical reasons, on the basis that a vote for their preferred candidate is likely to be wasted. In some electoral systems, it may be plausible for less-popular candidates to make similar appeals to supporters of more-popular candidates. In a plurality voting system, the term "wasted vote" is not usually applied to votes for the second-placed candidate, but rather to votes for candidates finishing third or lower. This is a reflection of Duverger's Law, i.e. the institutionalisation of a two-party system.
Opponents of the concept of a wasted vote point out that voting one's conscience is fundamental to democracy - an example of this is the adoption of major Socialist legislation by more mainstream parties in the United States in order to halt the Socialist party [1].
Consider an election where candidates A, B and C receive 6000, 3100 and 701 votes respectively.
If this is a plurality voting election for a single seat, Candidate A has a plurality of votes and is therefore elected. The wasted votes are:
If the same votes for A, B and C are cast in a d'Hondt method election for 12 seats, then the seats are split 8-4-0 for A-B-C. The wasted votes are:
A majority of votes are always wasted (in the wider sense) in a single-seat election, unless there are exactly 2 candidates and the margin of victory is exactly 1 vote. Multi-seat constituencies reduce the number of wasted votes as long as proportional representation is used. (When used with winner-take-all systems, as with the US Electoral College, multi-member constituencies may see the wasted vote reach or exceed 50%).