This fall, Ranked Choice / Instant Runoff Voting (IRV) will be on the ballot in Massachusetts. I'm voting for it, but only because it's better than the status quo, not because I think it's a very good voting system.
Massachusetts currently uses traditional majority ("first past the post") voting: whoever gets the most votes wins. Unfortunately, this only works well when you have two candidates. With more candidates, the candidates tend to hurt their allies by competing for the same pool of votes, making it more likely that an opponent wins.
In IRV each voter lists their preferred candidates in order, and if your first choice is eliminated then your vote goes to your next favorite. This mostly fixes the problem of minor spoiler candidates: anyone who is not a serious contender will get eliminated and their votes redistributed.
Unfortunately, IRV has major problems when you have more than two serious candidates. For example, even if there is a candidate that a majority of voters prefer to every other, they can still lose if their competitors happen to be eliminated in the wrong order. In Why Ranked Choice Voting Isn't Great I give examples of realistic situations in which IRV can give poor results.
While every voting method has cases it handles poorly, some are better than others. One attempt to compare them is called Voter Satisfaction Efficiency (more details). The idea is, you run a large number of simulations and see how different methods perform. It turns out that IRV does very poorly here, and if voters are highly strategic IRV does even worse than traditional plurality voting.
While I wish the voting method for us to consider were Approval (or maybe 3-2-1 or STAR), I do still think IRV is better than what we have today, and I'm planning on voting for it. One specific way in which IRV is an improvement is that it mostly doesn't, in its failings, benefit one type of party. This means that if we switch to IRV, and then as third-party candidates become stronger contenders we start to run into IRV's problems, it should be politically practical to switch to a better system. I do think there is some risk of setting back alternative voting systems in general by implementing an inferior version, but on balance I think the benefit of fixing the "minor spoiler" problem is likely larger.
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