[EM] Truncation and prisoner's dilemma

[Kevin Venzke]

 --- Bart Ingles <bartman at netgate.net> a écrit : > 
> > One of the main things I was arguing was that truncation doesn't benefit
> > the voter who does it (at least in cases where there is a CW).
> 
> Not entirely true, although this involves a prisoner's dilemma.  
> 
> If, in advance of the election, the vote count is not known, but A and C
> are believed equally likely to win in a head-to-head contest, the A and
> C factions can agree to truncate and block B from winning, thereby
> giving A and C each a 50% chance of winning.  This increases the
> expected utility of the outcome for both A and C, if B was a likely
> winner on fully-ranked ballots.

Ok, that's a possibility, but...

> Some believe a prisoner's dilemma strategy to be unworkable, since
> either side can "cheat" the other by failing to truncate, but the cost
> of being cheated seems low in this case.  If nothing else, it seems like
> a bit of a dilemma to decide how to play the prisoner's dilemma.

Yes, I think I would count it as unworkable, because in the context of
a single election, from the perspective of an individual voter, there
is no strategic incentive in permit Worst to beat AlmostWorst even if
there is a deal made beforehand.

If there are frequent elections, though, and stable blocs, voters
might take their credibility into consideration.

Kevin Venzke
stepjak at yahoo.fr

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