[EM] Strategy-free criterion

[Chris Benham]

Kristofer,

> Just to be sure I got what you were saying, this is in an imperfect 
> information setting, right? The B and C factions don't know which of 
> them have more first preferences than the other. 

Yes.

> IMHO, that seems like a significant flaw, because it potentially turns 
> party-neutral methods (IRV and STV) into something considerably closer 
> to party list. 

Not allowing truncation is always silly and unjustified.  GIGO.

I gather that historically preferential voting was introduced in 
Australia so that the relatively disciplined and organised Labor Party 
could be more easily defeated. If truncation was allowed then some lazy 
anti-Labor voters might do that.  It continues to be justified (among 
the few who even think about it) as being in the spirit of compulsory 
voting (which I agree does more good than harm.)

The scenario I described with 3 factions and no voters having a sincere 
second preference would be very rare and the apparent "flaw" of 
preferential methods that meet Clone Winner and Dominant Coalition in 
that situation is not one that I'm in favour of trying to address.

STV elections for seats in the Australian Senate are deliberately 
"corrupted" to resemble Party List PR. The voter has the option of 
voting for a party "above the line" which means that the voter blindly 
votes that party's full "ticket" (determined before the election and 
accessible to anyone interested).  Now if one votes "below the line" by 
numbering boxes next to the names of individual candidates you are 
allowed to partially truncate (but you still have to rank quite a few, 
maybe 12 candidates).

All this unnecessarily gives the party machines  unjustified extra 
power. They horse-trade among themselves as to where they'll direct 
preferences that voters don't care and probably don't even know about.

Chris B.


On 5/08/2024 12:01 am, Kristofer Munsterhjelm wrote:
> On 2024-08-02 19:35, Chris Benham wrote:
>> Now to talk about a problem of all preferential methods.  Say there 
>> are three factions of voters, each with its own candidate. Each 
>> faction strongly wants its own candidate to win and has no real 
>> preference among the other two, i.e. is about equally hostile to or 
>> disinterested in both of them.  Say it is known from polling that 
>> candidate A has about 50% support and candidates B and C each have 
>> about 25%.
>>
>> A is obviously the highest SU candidate, and with normal natural 
>> sincere say Approval voting all the voters will truncate two of the 
>> candidates and A easily wins.  But with a preferential system 
>> (especially one that meets Clone-Winner, as they all should) the B 
>> and C factions
>> have a huge incentive to do a preference-swap deal. That way each of 
>> them raise their chance of winning from zero to about 25%.
>>
>> In light of that, to some even a result like
>>
>> 49 A
>> 26 B>C
>> 25 C>B
>>
>> can look suspicious. Yes B and C are a perfect set of voted clones 
>> and a Mutual Majority and B is a voted Condorcet winner, but in the 
>> real world some might say that the B and C factions "ganged up" on A 
>> and "manipulated the election".
>
> Just to be sure I got what you were saying, this is in an imperfect 
> information setting, right? The B and C factions don't know which of 
> them have more first preferences than the other.
>
> I'm assuming that's the case because if they knew, then while the B 
> faction would be interested in doing a swap to flip the winner from A 
> to B, the C faction is indifferent to who wins out of A and B, and 
> thus wouldn't bother.
>
>> In Australia voting is compulsory and in most elections truncation is 
>> not allowed. This would be a big burden on voters who take it 
>> seriously if it wasn't for the regular custom of parties and 
>> sometimes independent candidates advising their supporters on how to 
>> complete their ballots. So a lot of voters are only thinking about 
>> which party should get their "primary vote", and the lower 
>> preferences are just some relatively arbitrary formality to ensure 
>> that their vote is counted.
>
> IMHO, that seems like a significant flaw, because it potentially turns 
> party-neutral methods (IRV and STV) into something considerably closer 
> to party list.
>
> Given that it does, it would make sense for the voters to treat higher 
> ranks as more important than lower ones - because if filling out lower 
> ranks is a chore, then voters would focus on higher ranks.
>
> Say a voter "independently ranks" those candidates where he neither 
> copies some other advice or ranks randomly, and "fills" the other 
> candidates (for lack of better terms).
>
> Then it's possible that the connotation of lower ranks as something 
> that you fill, not independently rank, carries through to the point 
> that voters independently rank fewer candidates than they would 
> explicitly rank if they could truncate.
>
> IRV and STV's focus on higher preferences might also contribute to the 
> voters' focus, but it's hard to say what the direction of causality is 
> there: whether these methods were adopted because the public was used 
> to Plurality-style reasoning, or if their (particularly AV's) 
> compromise incentive leads the voters to focus further on first 
> preferences.
>
> -km