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Comment by gene91 | Hacker News Reader

https://www.fairvote.org/rcv_faq#monotonicity

Read "22. Does RCV satisfy the monotonicity criterion?"

Say, there's 3 candidates. You want A to win. You think A will lose to B in a 1-on-1 match, but would win C. So you vote C-A-B (or C-B-A, doesn't matter) to increase the likeliness that B got eliminated in the 1st round. Of course, you're now saying that you prefer C over A in a 1-on-1 race. But that's fine because other people will vote for A.

Concretely, let's say this is people's actual choice.

31 B-A-C; 39 A-B-C; 30 C-B-A

B wins.

Now, if 2 people preferring A (voted A-B-C) strategically change their vote to C-B-A.

31 B-A-C; 37 A-B-C; 32 C-B-A

Now, A wins.

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I simply don't get why the person preferring A doesn't rank A first. This scenario only works if you have exactly 3 candidates and the numbers are tight and everyone is tactically voting instead of voting their conscience.

In reality most preferential voting schemes have many candidates, and there's too much chaos to coordinate this kind of scenario.

Meanwhile plurality voting has candidates winning with way less than 50% of the vote, and claiming some mandate from god.

The sooner we ditch FPTP the sooner we get to something like Condorcet, or STV with multimember districts.

> I simply don't get why the person preferring A doesn't rank A first.

Well, that's kind of the point of the example. A normal person who wants A to win would put A as their first choice. But doing that can actually cause their preferred candidate to lose, which is exactly the opposite of the voter's intent. FPTP has a different set of problems that one could argue are worse, but one of the few good things about FPTP is that you can't say about some election result "that candidate lost because I voted for him/her".

Non-monotonic results don't happen in every election, but they're something that can happen.

It just doesn't feel likely that this could be successfully coordinated or occur in a decentralized way organically in a sufficiently large election.

Consider how little trust a lot of people have in polling. You would need a very high amount of trust in it if you were going to dishonesty rank your choices based on it. And if strategic voting is going to be based on polling, wouldn't we expect people then start strategically lying to pollsters?

The system has too much chaos.

An individual person might not be able to coordinate such a thing, but you can bet that campaign strategists are going to be very interested in crafting their messages to get the results they want. I mean, right now we have campaigns and PACs that sometimes promote a minor candidate they're ideologically opposed to because they'll siphon votes away from their major-party opponent.

What strategies will they employ in RCV elections? I don't know, but given the way campaigns already operate with continuous polling, elaborate voter databases, and modern ad-tech that can target exactly the right message to exactly the right people to influence their behavior slightly, I see election systems with wonky outcomes as an attack surface against democracy.

> The system has too much chaos.

There's too much fog-of-war for individual voters to make optimal strategic voting choices, but the Cambridge Analyticas of the world can use that to their advantage. I don't like that information asymmetry, and it seems the best way to defend against it is to have voting systems that are as close to the ideal (which is that candidates win by having the most public support) as possible.

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