Comment by typest | Hacker News Reader

Comment by typest | Hacker News Reader

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Most surprising consequence is probably that IRV is unlikely to break 2 party dominance, even though it this is an often claimed advantage of IRV.

The frequently imagined scenario with IRV is that, in a two party system where most people will rank 1 of 2 parties first, then a small percent of voters can safely rank a third party first. This party is then eliminated, but not before a surprisingly strong showing (e.g. 5% first rather than the .05% we currently have). This would likely happen.

The problem arises in the next election, when the third party is now strong enough to command a large percent of first place votes. Since the party with the least first place votes is eliminated (even if they have a ton of second place votes), the third party now stands a real risk of cannibalizing votes from the next most similar "mainstream" party. If this cannibalization were to occur, both parties could lose to the other mainstream party that many voters might not have preferred! Due to this risk, it's likely voters would strategically rank the third party below the mainstream party even if that wasn't their true preference. In this way, IRV can still lead to 2 party dominance.

Assume for the sake of argument that the policy of the "third" party is just like that of the "second" of the two "main" parties. In that case, it's true that the second party could be eliminated in the initial round of voting. However, all its votes would then transfer to the third party. In that case the third party very well could beat the "first" party, satisfying supporters of both the second and third parties.

It's true that third parties would be unlikely to map to the current political spectrum in such a "pure" fashion. However, that just means that voters reject the political choices currently on offer. Voters really should have that option.

I think you have two incorrect assumptions here. You're assuming A) that parties and political ideologies exist in 1 dimension, and that B) the second party is closer to the third party than the first, such that its votes will go to the nearest neighbor, which is then the third party.

Even granting A, B is definitely not true. There are many similarities between the two major parties, and removing one in favor of a third party would likely split voters between the third party, and the other major party.

Also, A is not true either, so the distance between parties becomes even more unclear.

I for sure believe voters should be able to reject the current political choice on offer! I support IRV over our current system for sure. But, my main point is that IRV is actually not what many people believe it to be, and is far worse than other, simpler systems, such as approval voting.

This whole thread is a thought experiment. I made a single simplifying assumption, for the sake of clarifying the particular qualities of that thought experiment: that voters would understand the policies of the second and third parties to be identical. In that case, IRV isn't "unlikely to break 2 party dominance", as you claimed above. So, that claim isn't universally true. It might be true in some circumstances, but we don't know what those might be. You'll need to explain more carefully why we should reject RCV in favor of some more perfect alternative.

IRV fails the favorite betrayer condition and isn't monotonic.

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