Preferential Voting
Where voters rank their preferences
When voters need to select one choice from 3 or more, it is often the case that none of the choices receives a majority (more than half) support.
One approach is to simply vote again, and again, until finally one person does get a majority. This approach may in practice need to allow for new nominees to be added to the list, so a compromise candidate can be selected.
Two historical instances of this approach are of interest: "In a city council election in Massachusetts 114 votes were taken before a choice was finally made for president of the council. In a national political convention the delegates voted 103 times before a choice was made of the nomination of President of the United States." -- Demeter's Manual of Parliamentary Law and Procedure, George Demeter, 1969, p. 247.
A Plurality voting system says the choice with the most votes wins. Although simple and thus popular, a majority faction with two candidates may split the faction's vote such that the minority faction's single candidate gets the most and wins. Sometimes a minority faction secretly instigate the candidacy of a 3rd person who they hope will siphon off some of their chief opponent's votes.
One approach to solving the vote-splitting problem of the plurality system is to have a primary election, with the top two advanced to a runoff election. This approach does nothing to solve the vote-splitting in the primary, of course. Who's to say that candidate's #3 and #4 didn't split a faction's vote that totals more than #2's vote?
This observation has lead to the notion of a series of run-offs, each dropping only the lowest vote-getter. Thus if #4 is eliminated and his supporters vote for #3 in the runoff, #3 may pull ahead of #2, who would then be dropped, resulting in a final runoff between #1 and #3. Of course with 5 candidates you may have to have 4 rounds of voting, and whether at a convention or at the public office voting polls, this can be very time consuming and costly for voters and candidates.
Instant Runoff Voting (IRV) accomplishes the same thing but with a single campaign season and single ballot. Voters rank their choices on a single ballot. Instead of simply voting for Ames, the voter ranks Ames as 1st choice, Beck as 2nd choice, Carr as 3rd choice. Each ballot is counted for the highest ranking candidate on the ballot.
If no one has a majority, the lowest vote-getter is dropped and an instant runoff is held with the remaining candidates. In the runoff, as before, each ballot is counted for the highest ranking candidate in the runoff. Practically speaking, only the ballots for the dropped candidate will now be counted differently than before.
Again, if no one has a majority, the lowest vote-getter is dropped and another instant runoff is held, repeating the process until someone wins a majority.
IRV is also called Ranked Choice Voting (RCV), Preferential Voting (PV), Alternative Voting (AV), the Hare system, the Hare method, and Single Transferable Vote (STV). See http://en.wikipedia.org/wiki/Instant_runoff_voting.
The RCV, PV and AV names focus on the way voters mark their ballots indicating a ranking or preference, whereas the IRV and STV names focus on how the ranked ballots are counted.
Other methods of counting ranked ballots include the Condorcet Method and the Borda Count. See http://en.wikipedia.org/wiki/Preferential_voting.
RCV-IRV Frequently Asked Questions
1. If you transfer the votes for the dropped candidate to the next higher ranked candidate on those ballots, aren't those voters getting to vote twice, in violation of the one-person-one-vote rule?
Answer: No. A runoff election is in essence held, where ALL voters and ALL ballots are counted. Citing a one-person-one-vote violation is as spurious for RCV-IRV as it would be for the traditional runoff or primary election system.
2. There seems to be a possible strange scenario whereby a candidate who would otherwise win, by getting another candidate's supporters to switch to support him, may thus lose. How can this be justified? For instance, shortly before the election
9 voters prefer Ames 1st, and other rankings aren't relevant to this example;
8 voters prefer Beck 1st, Carr 2nd, Ames 3rd;
7 voters prefer Carr 1st, Ames 2nd, Beck 3rd.
Under RCV-IRV, Carr is dropped, and Ames wins.
But if Ames gives a great speech that gets 2 of B's supporters to switch to making A their 1st choice, the ballots are cast this way:
11 for Ames;
6 for Beck 1st, Carr 2nd, Ames 3rd;
7 for Carr.
Beck is dropped, and Carr wins! Why should Ames, who would have won without getting more support, now lose?
Answer: Good point! This theoretically could happen, BUT there are several points that need to be understood here.
First, the exact same thing can happen in a top-two primary (runoff) system.
Second, no election system is perfect.
See:
http://en.wikipedia.org/wiki/General_Possibility_Theorem
http://en.wikipedia.org/wiki/Gibbard%E2%80%93Satterthwaite_theorem
Third, the concocted example is akin to having a tie in an election; both are very rare.
Fourth, RCV-IRV has the advantage over other PV systems in that it uses a majority winner philosophy, which is familiar to the public, as is the runoff.