Instant Runoff Voting (IRV) has been officially endorsed by several organizations and is gaining momentum. Unfortunately, however, confusion reigns regarding its advantages and disadvantages. IRV is very good at preventing minor parties from interfering with the two-party system, but it is arguably no better than our current plurality system at expanding the two-party system and giving other parties a chance to actually win elections. Furthermore, if a third party ever does become strong enough under IRV to seriously threaten the two major parties, they could hurt their own cause and wreak havoc with our entire political system, just as they could under our current plurality system.
IRV can prevent the spoiler effect, in which a minor party splits the vote with a major party and tilts the election toward the other major party, hurting its own cause. IRV therefore seems to allow supporters of minor parties to cast protest votes without "wasting" their votes. This advantage is illusory, however, because it applies only as long as those minor parties are sure to lose. As soon as one of those minor parties threatens to become a major party and actually win, its supporters vote for them at the risk of hurting their own cause, just as in the current plurality system. Under IRV, votes for minor parties are therefore symbolic at best, or dangerous at worst. An example will illustrate why.
Suppose my true preference is for the Libertarian first and the Republican second. Suppose further that the Libertarians are the strongest "minor" party. At some round of the IRV counting process, all the candidates will be eliminated except the Republican, the Democrat, and the Libertarian. If the Libertarian then has the fewest first-choice votes, he or she will be eliminated and my vote will transfer to the Republican, just as I wanted. But what if the Republican is eliminated before the Libertarian? Unless all the Republican votes transfer to the Libertarian, which is extremely unlikely, the Democrat might then beat the Libertarian. If so, I will have helped the Democrat win by not strategically ranking the Republican first. But that's the same situation I'm in now if I vote my true preference for the Libertarian!
What happened in the above example is that IRV essentially ignored one of my key preferences. By voting (Libertarian, Republican, ..., Democrat), I increase the chances that the Republican will be eliminated before the Libertarian. If that then happens, my preference for the Republican over the Democrat is essentially discarded or ignored. This is the fundamental problem with IRV. The only preference that is sure to be counted is my first choice. The problem gets worse as the number of candidates increases. The outcome of the election can depend in a very quirky way on the order in which candidates are eliminated for having the fewest top-choice votes. The only way a voter can be assured of not wasting his or her vote is to rank one of the two major parties as their first choice, which is precisely what happens now under plurality voting.
The example is hardly contrived. The "lesser of two evils" problem is almost guaranteed to rear its ugly head again under IRV. Until a minor party is strong enough to win, a first-choice vote for them is essentially only symbolic. After a minor party is strong enough to win, on the other hand, a vote for them could have the same spoiler effect that it could have under the current plurality system. Hence, if IRV is ever actually adopted, we will likely remain stuck in the old two-party system, just as Australia still is, despite the fact that it has used IRV since around 1920. On the other hand, if minor parties do somehow manage to become competitive under IRV, they could wreak havoc with our entire system of government. As in our current system, the stronger a minor party becomes, the more it could hurt its own cause.
In other words, IRV can have either of two completely opposite effects, depending on whether a third party is truly competitive or not. Before a third party is competitive, the effect of IRV is equivalent to a plurality system in which all supporters of minor parties are somehow convinced to abandon their principles and vote for the "lesser of two evils." Yes, those voters get the satisfaction of knowing they voted for the party and the candidate they truly prefer, but their first choice is eventually eliminated and has no effect on who actually wins. After a third party is competitive, on the other hand, the effect if IRV is equivalent to a plurality system in which many voters are somehow convinced to forget about strategy and vote sincerely. As most intelligent voters know, that would wreak havoc with the stability of our political system.
IRV has been said to make strategic or defensive voting very difficult. But strategic voting is difficult under IRV only after more than two parties are truly competitive. Before that time, strategic voting is essentially the same as what it is in our current plurality system: rank the "lesser of two evils" candidate as your first choice. As soon as more than two parties are truly competitive, strategic voting could indeed become very difficult because the "lesser of two evils" concept no longer applies when more than two parties are competitive. However, this difficulty, far from being an advantage, is actually a huge disadvantage. Voters will then need to vote strategically but will be unable to figure out how to do so, except to revert back to the old two-party paradigm. Hence the original duopoly will remain intact. In other words, IRV will not solve the classic "lesser of two evils" problem that plagues plurality voting.
IRV does have one possible advantage over our current plurality system: it could be a step toward true electoral reform in the form of Condorcet voting, which is far superior to IRV. The actual voting mechanics of IRV and Condorcet voting are identical. In both IRV and Condorcet voting, the voters rank the candidates, and the required voting equipment is the same for each. The only difference is the actual algorithm (and its implementation software) for determining the winner. In other words, the "front end" is common for IRV and Condorcet voting, and only the "back end" is different. From a purely technical perspective, that "back end" software would be very easy to replace, but the political perspective is another story altogether, of course. If IRV is widely adopted, it could be transitional to true reform -- or it could become entrenched.
IRV has other serious problems too, which are explained in more detail elsewhere at the website. It is an erratic voting system because ranking a candidate higher can actually cause the candidate to lose, and ranking a candidate lower can cause the candidate to win. As if that weren't bad enough, it can also fail to elect a candidate who is preferred over each of the other candidates by a majority of the voters. It is also much more difficult to implement with security and integrity because the votes cannot be summed as in most other election methods.
In summary, IRV is a deceptive and potentially dangerous non-reform masquerading as a reform. If adopted, the cure could be worse than the disease. Once the inadequacy of IRV becomes clear in actual practice, it could disillusion the public with electoral reform and thereby close the door to true reform. The stakes are way too high to get this one wrong. We can only hope that the well-intentioned and devoted advocates of IRV are still open-minded enough to recognize this reality. The battle for electoral reform will be difficult enough without insurmountable ignorance within the reform movement itself.
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