How Proportional RCV Works

CCD_Grid.jpgVoting and vote counting under proportional ranked choice voting is similar to single-winner ranked choice voting, except that instead of one candidate winning with a majority of the votes, several candidates win, each with their own smaller share of the votes.

Every voter has exactly one effective vote, and so candidates can win by earning votes from distinct groups of voters. In practice, this means that nearly every voter will help elect a candidate they support, and different groups of like-minded voters will elect candidates in proportion to their numbers.

To vote, voters rank their choices, just like in any other form of ranked choice voting. Voters can rank as many or as few choices as they want to.

To win, a candidate must earn a sufficiently large share of the votes. This share of votes is called the threshold. The threshold is always the smallest number of votes that mathematically guarantees that the candidate will be one of the winners. For example, if three candidates will win, the threshold is 25% of the votes plus one additional vote. That is because if a candidate has that many votes, it is impossible for three other candidates to beat them - there are not enough total votes left over for that to be possible.

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Votes are counted in rounds. If a candidate has enough votes to win in a round, then they are elected and a new round begins. If no candidate has enough votes to win in a round, then the candidate with the fewest votes is eliminated and a new round begins. This repeats until all of the winners have been selected.

When a candidate is elected, any extra votes in excess of the threshold would be wasted on them, and so such surplus votes are instead counted for the voters' next choices. This can be done many different ways, but the best way is to transfer a fraction of every vote to its next choice. That way, every vote is treated equally and no part of any vote is wasted.

When a candidate is eliminated, all of the votes counting for them are added to the totals of their next choices. That way, no votes are wasted on a candidate who cannot win.

In every round, every ballot always counts for the highest ranked candidate that still has a chance to win. By counting in rounds, proportional ranked choice voting ensures that every vote is very powerful, that voters do not need to think tactically about how to avoid their vote being wasted, and that the candidates who win each represent a roughly equal number of voters.

For a more detailed explanation, including a table showing results from a hypothetical election, see our Proportional RCV Example page.

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