How do instant runoffs work?

Question

I've read that some elections have instant runoffs. What are they and how do they work? How do they differ from a standard majority vote election?

Answer 1

In an IRV (instant-runoff voting) system you do not simply vote for one option, but you can rank options according to your preferences. Imagine that three candidates stand for election as mayor in your town.

• Candidate A (25%)
• Candidate B (30%)
• Candidate C (45%)

In order for any candidate to win he would need at least 50% of the votes. Given that no candidate got the necessary votes, a runoff election will be held between the two strongest contenders. Normally this happens a while after the first election round.

By using IRV you can conduct the runoff election directly after having counted the first round. As voters indicated their preferential ranking, you can eliminate the weakest candidate and redistribute the votes on his ballots according to the indicated second preference. This will be continued until at least one candidate gets 50% of the votes attributed to him.

Everything happens in one election but is counted as often as there are rounds needed for one candidate to get at least 50% of the votes. Only in rare occasions can it happen that you need to conduct a second round of actual voting.

In conclusion do they differ from standard majority elections that you always get a candidate that has at least 50% of the electorate backing her and you can do it in one single round of voting.