[EM] Approval vs. IRV

[Juho Laatu]

On 29.11.2011, at 6.07, C.Benham wrote:

> In IRV if you are convinced of that you have no compelling reason to compromise because you
> can expect F to be eliminated and your vote transferred to C. No, to have a good reason to compromise
> you must be convinced that F *will* be one of the top 2 (thanks to your vote) displacing C, but will
> nonetheless lose when C would have won if  you'd top-voted C.

I guess F could cause (the otherwise winner) C to be eliminated, and F could be eliminated already before F reaches the top 2 position (40: A, 15: C, 25: E>C, 20: F>C). But anyway, it is less risky to top rank one's favourite in IRV than in FPP.

We may compare IRV also to the other commonly used single-winner method TTR. To be brief, one could say that IRV is better than TTR since it has more elimination rounds. IRV's problem in this comparison is that it collects so much information that one can, after the election, see what strategies would have paid off. In TTR one may have very similar problems but people stay happier since they can not see the problems. They can't see for example what would have happened if some other pair of candidates would have made it to the second round. Spoilers may exist but they remain undetected, or at least unverified.

People seem to be reasonably happy with TTR. The random nature of TTR seems to be just part of the competition (rules that are equal to all) in the minds of the voters. The elimination based algorithm of IRV may also look pretty natural and fair to regular voters. It takes some effort to explain to them that in some cases the IRV results might not be ideal. Maybe people don't care that much about the complex details.

> In my opinion IRV is one of the reasonable algorithms to use with ranked ballots, and the best for those
> who prefer things like Later-no-Harm and Invulnerability to Burial to either the Condorcet or  FBC
> criteria.

I'd like to add that IRV is an algorithm for those that want to favour the large parties. In some environments this might be intentional, and in some a problem. I note that also in Condorcet methods voters can trust that betraying their favourite or burial are very probably not useful strategies for them, and the risk of later preferences causing some harm is small.

If one specifically wants Condorcet winners to win the election, then IRV may not the the best choice. With three candidates the centre candidate will be eliminated if it has less first preference support than the others. This property is related to the (above mentioned) question on whether one wants to favour large parties (with lots of first preference support) or not.

Approval is maybe a reasonable algorithm for non-competitive elections where two rating values are sufficient.

Juho