Maine passes Ranked Choice Voting

post by morganism · 2016-11-14T20:07:02.003Z · score: 6 (7 votes) · LW · GW · Legacy · 7 comments

This is a link post for,_Question_5_%282016%29


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comment by Daniel_Burfoot · 2016-11-15T18:21:44.407Z · score: 2 (2 votes) · LW · GW

It's not clear to me that this will be good or bad for Maine, but it is certainly good for the rest of humanity, because we will all benefit from observing the results of the change.

comment by Luke_A_Somers · 2016-11-15T15:55:54.547Z · score: 1 (1 votes) · LW · GW

It would have been even nicer if they'd changed to a system with fewer pathologies than IRV, like Schulze or Ranked Pairs or Score or Approval...

but I'll take what I can get!

comment by roystgnr · 2016-11-18T18:03:37.826Z · score: 0 (0 votes) · LW · GW

The form of the pathologies makes a difference, no?

IIRC the worst pathology with IRV in a 3 way race is basically: you can now safely vote for a third party who can't possibly win, but if they show real support then it's time to put one of the two Schelling party candidates in front of them. So it's not worse than plurality but it's not much of an improvement. Plus, with more candidates IRV becomes more and more potentially insane.

With Schulze or Ranked Pairs the pathology is DH3: If a third party can win, you can often help them win by voting a "dark horse" candidate ahead of their two real competitors... but if enough people try that then the "dark horse" actually wins. That could actually end up much worse than plurality.

With Score the unique pathology is: If you know how to vote tactically then your vote is almost certain to look like an approval vote. So the only reason to use it rather than Approval is to encourage non-game-theory-geeks to sabotage themselves and water down their own votes.

With Approval (and Score, to a slightly lesser extent) the pathology is the "Burr dilemma". Okay, if Approval voters are good at tactical voting and there are many iterations of accurate public polls, then they pick the Condorcet winner... but if either of those things aren't true then people attempting to vote tactically can end up hurting front-runner candidates and electing a "dark horse".

I'd say this all starts to make plurality look reasonable by comparison, because the two party system tends to only fail by electing overly-conservative (in the Burkean sense) candidates, which is a less dangerous failure than its opposite would be, but I admit there is a recent very-salient counterexample.

comment by Luke_A_Somers · 2016-11-22T17:15:03.654Z · score: 1 (1 votes) · LW · GW

With Schulze or Ranked Pairs the pathology is DH3: If a third party can win, you can often help them win by voting a "dark horse" candidate ahead of their two real competitors... but if enough people try that then the "dark horse" actually wins. That could actually end up much worse than plurality.

That's very, very hard to pull off in practice, and it's obvious to anyone who descends from the omniscient view to an actual campaign.

Suppose there's the A party(45%), the B party(40%), and the generally-disliked C party (15%). In order for B not to be the Condorcet winner already but make it as easy as possible for DH3, let's suppose that C is evenly split on the A vs B issue. This is nearly the ideal case for DH3. Picking a lower- or higher-scoring party would present a somewhat different set of challenges.

The DH3 strategy is for B to lie and say that C is better than A, so as to create a cycle, and then win it. A has a lead over B of 45-40=5%, and a lead over C of 85-15=60%. B also has a lead over C of 85-15=60%.

B needs to get A to lose to C by an amount greater than A's lead over B, but less than B's lead over C. Each percentage point of B's strategic votes of C over A shifts A's lead over C down by 2%. So, if they can get that +60 down to -7 or something, then A's lead over B will be the smallest one.

But look at what actually has to happen for B to win this cycle:

1)First, they need to successfully create the cycle, which means getting a huge number of their people on board (>13/16 of them). This cannot be done secretly.

2) A voters need to reliably prefer B over C. If B was campaigning in favor of C, then some A voters could be lured away legitimately. If B was issuing ballot instructions to put C above A, some A voters could think that's so bad they will put B at the bottom, again legitimately. The entire strategy relies on A voters cooperating with the B party in stealing the election, and B's pursuing this strategy could well make them worse in A's eyes than C would have been.

Each percentage point of A voters who votes for C over B pushes B's lead over C down from 60% by 2%. Supposing that B got 90% of their voters on board with the strategy (good luck with that), then C's lead over A would be 12%. A voters would have a smaller swing to achieve (+ 60% down to +11% instead of +60% down to -6%) and more voters to do it with (45% instead of 40%). So, instead of having to strategically vote with 65/80 of their party, they need to partially-strategically, partially-honestly vote with 44/80 of their party.

3) ALSO, the C voters could stay neutral or break either way in this, and become decisive. B needs them not to break against B, at least. If B gets C voters to rank B above A (as they might considering how B has been acting), then sure, B wins, but they have done it by forming a coalition with C, which is, you know, a legitimate political move, and not a failure of an election system.

Only if all of these go just right does B succeed. Failing in 1 does nothing good, and helps the disliked C party, making it look much more popular, which is a bad idea even in the medium term. Failing in 2 gives the win to C, which is of course terrible. Failing in 3 loses to A again like 1; and doing better than marginally succeeding in 3 makes B's victory actually legitimate.

Anyway, in the thousands of actual elections held by the CIVS, nothing like this has happened, and for good reason. It's lunacy.

comment by Gurkenglas · 2016-11-19T12:10:20.568Z · score: 0 (0 votes) · LW · GW

This is not the sort of change that should be passed with a 52% vote. Although if it required 67%, the first article like this we'd be reading would be about it being passed somewhere with 68% or so I guess.

comment by mk54 · 2016-11-15T22:24:24.784Z · score: 0 (0 votes) · LW · GW

Paul LePage arguably won the governorship in 2010 because his opposition was fractured. He received 37.6% of the vote, while an independent candidate received 35.9% and a Democrat received 18.8%. He's fairly unpopular, so I wonder if that was a major driver for this. It also makes me wonder if ranked voting would be as successful in other states. Definitely a good thing though.

comment by WalterL · 2016-11-15T14:02:45.947Z · score: 0 (0 votes) · LW · GW

Alright! Way to go Maine!