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Comment by elihu | Hacker News Reader

The problem with RCV is there's a big difference between giving an honest opinion and voting tactically.

In RCV it's safe to put your first choice first if either they're an overwhelming favorite to win, or they're so weak they're sure to get eliminated right away. If it's a close three-way election, you might cause your favorite candidate to lose by ranking them first. It's hard to develop any kind of intuition around how your vote will impact the race in these situations -- I think in the long run voters tend to learn that voting for third parties isn't safe, so two parties continue to dominate.

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> If it's a close three-way election, you might cause your favorite candidate to lose by ranking them first.

Could you explain that? I can't think of a situation where putting the candidate I want to win as #1 would cause them to lose. Ranking other close candidates as #2/#3 could cause my #1 to lose, but I don't think voting for someone as #1 alone would possibly harm them.

So what I think the parent is referring to is called the Favorite Betrayer Criteria[0]. The short is that there are two forms of the spoiler effect: strong and weak. RCV handles the weak case but does not handle the strong case. I explain part of why cardinal methods handle the strong case in this comment[1]. The truth is that we're far more concerned with the strong case than weak case because from our current position this is the more frequent type of spoiler (and arguably is more frequent in general).

[0] https://electowiki.org/wiki/Favorite_betrayal_criterion

[1] https://news.ycombinator.com/item?id=33111242

I wonder if fixing the "strong case" spoiler actually is NOT what some "spoiler voters" would want, simply BECAUSE they want to spoil for the other party to try to move that party toward where they want it to be.

Probably. But I don't think the public really wants their voting systems to be highly vulnerable to strategic voting. That does just give elites an edge and ends up with less equitable representation.

(strategies exist for ALL voting systems. But not all strategies are equally as bad)

Also, not all "strategies" fit people's intuitive notion of "strategy", which is colored by FPTP having a really glaringly awful strategic incentive for dishonest voting.

Most cardinal systems make it difficult to vote strategically. That's actually what the difference with star and score is about. But this is also why so many in the thread are talking about monotonicity and favorite betrayer. Failing these criteria means your voting system is highly susceptible to manipulation. Essentially allowing candidates to win that shouldn't have won.

> not all strategies are equally as bad

That's an important point. Also, just because a strategy exists in theory, doesn't mean that in practice any voter can confidently find that strategy (since they lack perfect information about how all the other voters intend to vote).

Let's say you have three candidates A, B, C.

A is left, B is center, C is right leaning.

Polling shows that voters are leaning:

- 15% BAC

- 15% BCA

- 25% ABC

- 45% CBA

If everyone voted as they desired, then the instant runoff would be between B and C, with B winning with 55% of votes.

If a subset of C voters instead strategically vote ACB (6%), this would change the runoff to be between A & C, with C winning 60%.

First, a run off between A and C wouldn't have C with 60%. C would have 54%, the 6% of C voters would have to come from CBA. And if A is in the runoff, that 6% stays with A.

These are post facto strategies though. You can only implement that strategy if you can guarantee all of that information. Which you can only do after the election.

The first problem is that polling is an estimate. If you are wrong by a couple of percentage points, the strategy fails. If the results come back 16 (BAC), 16 (BCA), 23 (ABC), 39 (CBA), 6 (ACB), B now has 32 first votes and A only has 29.

Next is getting the right number of people to comply. You could easily just mess it up and have either not enough or too many people cast the strategic ballot. If only 4% or less vote ACB, the plan doesn't work. If 11% or more vote ACB, A wins.

In the end, strategic voting is a bit like voter fraud, talked about way more than is actually done. And implied to be a much bigger problem than it ever could be.

Oh I don't disagree, and am in the strong support of anything that moves away from FPP. The only addition I will make is that these (potentially unfounded) fears is what leads people to continue to vote strategically, such as voting BAC instead of ABC to avoid the potential of C using the strategy.

And just to be clear, this makes sense.

Because the relevant fact here isn't that some CBA voters put A at the front (ACB). It's that they moved B from 2nd to 3rd. So of course, that lessens support for B, so B no longer wins.

People seem to present this as a flaw, when it's reflecting actual changes in voting. And this is basically impossible to do so strategically, because nobody has this level of accurate detail prior to the election.

The only issue is that the (potentially unfounded) fear of strategic voting on the other side leads people to vote strategically in the same FPP manner by voting ABC instead of BAC to avoid C. But I greatly long for anything that moves us from the anti-democratic FPP.

> you might cause your favorite candidate to lose by ranking them first

That's a flawed characterization that keeps getting repeated.

As I explain in another comment below, in theory you could get your favorite candidate to win by further downranking the candidate who would otherwise win. One way of accomplishing that is to move other candidates up higher above your actual preferred candidate.

But in reality, there's no way to know what the exact precise vote breakdowns will be, so voting strategically (lying about your preferences) is impossible in a practical sense. There's no intuition to develop -- just vote your preferences.

It isn't a flawed characterization. It is called the Favorite Betrayer[0] (also known as Strong Spoiler Effect) and has been seen in practice. We should also talk about rank's failure of the Monotonicity Criterion[1][2] because that's relevant here too.

To claim it is impossible in practice is to deny history.

[0] https://electowiki.org/wiki/Favorite_betrayal_criterion

[1] https://electionscience.org/library/monotonicity/

[2] https://electowiki.org/wiki/Monotonicity

> I think in the long run voters tend to learn that voting for third parties isn't safe, so two parties continue to dominate.

The empiricval evidence in countries with long term ranked voting (Australia, say) is that bicameral party systems (only Democrats or Republicans have any realistic chance) wither and die, and smaller blocs have a better chance of survival and impact | influence in the House and Senate ..

Two parties "dominate" in Australia (or rather three parties, which are effectively two - the Nat-Liberals being an Rural-Urban conservative coalition of long standing) but nowhere near the degree to which two parties dominate in the USofA; more importantly minority opinions have gravitas and can sway the major vote - none of this bipolar US Dem-Rep deadlock.

Also it’s not just about the nominal parties that win, it’s the composition of politicians in those parties, and RCV selects for more broadly agreeable candidates.

I think comparing the US to others is often a bad comparison. Most others have coalitions and you'll find that two coalitions dominate. In the US parties act as coalitions. We can see the wide range in opinions from people like Warren/Sanders/AOC compared to those like Pelosi/Biden/Harris. Even in the Republican side you have this massive division, though they've been more effective lately at achieving a party over principle strategy. So two coalitions isn't really any better than what's here in the US because it is in essence the same thing.

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