[EM] My Favorite Deterministic Condorcet Efficient Method: TACC

[Jameson Quinn]

2010/11/10 C.Benham <cbenhamau at yahoo.com.au>

>  Chris wrote ...
>
> >* 31: A>B*>* 32: B>C*>* 37: C>A*>**>* Approvals: B63, A68, C69. A>B>C>A.*>**>* TACC elects A, but C is positionally the dominant candidate and*>* pairwise beats A.*>**>* For a Condorcet method with pretension to mathematical elegance,*>* I don't* *see how that* *can be justified.*>**>* Chris Benham*>**>* PS: Could someone please refresh our memories: What is the*>* "Banks Set"?*
> Forest Replies:
>
>
> As you know C is the DMC winner, and would be a slightly better winner, given
> that the ballots are sincere.  But DMC is not as burial resistant and truncation
> resistant as TACC.
>
> It is interesting that DMC and TACC have opposite rules for which of the top two
> approval members of the top cycle (of three) wins.  DMC awards the win to the
> one (of these two) that beats the other.  TACC awards the win to the one that is
> beaten by the other.
>
> Chris: I have long since abandoned the "Definite Majority Choice" (DMC)
> method in favour of Smith//Approval (as my preferred Condorcet method),
> which also elects C here. I still like the Definite Majority criterion,
> which says that no candidate that is pairwise beaten by a more approved
> candidate is allowed to win. I think that (in isolation) meeting the
> Condorcet criterion is desirable, but not so holy that on discovering there
> is no voted CW the method should proceed on the assumption that there is
> really a "sincere CW" that has been victimised by strategists the method
> should try to frustrate or punish. Condorcet methods are vulnerable to
> Burial, period. Futile attempts to address this should not be at the expense
> of producing winners that can have no philosophical justification on the
> assumption that all the votes are sincere (or are all equally likely to be
> sincere). The TACC winner A simply has no shred of justification versus the
> Smith//Approval winner C. Forest:
>
> I've come around to the belief that most Condorcet cycles in ordinary elections
> are artificial, so chances are that this cycle was created from the burial of B
> by the C faction.  Giving C the win only rewards this manipulation.
>
> Chris: I can't see any remotely rational justification for assuming that
> this is the case rather than, say, the cycle was created by the A voters
> burying C.
>
>
The rational conclusion would be that the most probable burial, is the one
that favors the actual winner. That is, you can't assume that the ballots
exist independently of the system being used. If that is so, then Chris is
right: it is essentially futile for a Condorcet method to try to
de-incentivize burial. That's not true, though, for truncation; and
remember: in the real world, strategy will not be unanimous, so attempted
burial will tend to look similar to probabilistic truncation.

So, for its truncation resistance, TACC seems to me to be a
better-than-average, but not outstanding, Condorcet method. So far, though,
that's just based on arbitrary examples; I'd certainly be happier if there
were some rigorous truncation-resistance property which TACC could be shown
to [probabilistically?] meet.

JQ
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