[EM] Advantages of the two-round system vs Schulze method and contingent voting

[Peter Zbornik]

Hi Kristofer,

thanks,

so is it right to state, that:

"The only advantage of Contingent vote before Schulze in terms of satisfied
criteria is in the case of three candidates, where the Contingent vote
satisfies Later-No-Harm"?

Peter

On Thu, Jun 17, 2010 at 2:00 PM, Kristofer Munsterhjelm <
km-elmet at broadpark.no> wrote:

> Peter Zbornik wrote:
>
>> Hello,
>>
>> an other question I wonder if you could help me with:
>> For single winner elections we currently use the two round system, which
>> is equivalent to the Contingent vote providing that the voter does not
>> change preferences see http://en.wikipedia.org/wiki/Two-round_system and
>> http://en.wikipedia.org/wiki/Contingent_vote
>>
>> <http://en.wikipedia.org/wiki/Contingent_vote>According to the table on:
>>
>> http://en.wikipedia.org/wiki/Schulze_method#Comparison_with_other_preferential_single-winner_election_methods
>> ,
>> Contingent voting <
>> http://en.wikipedia.org/wiki/Sri_Lankan_contingent_vote> has no advantage
>> over Schulze method (apart from being a few dimensions simpler in terms of
>> vote count and understandability for the common person).
>>
>> Two-round voting (although widely used) is not listed in the table.
>>
>> The questions are: 1) Does the two-round system satisfy any criteria,
>> which Schulze method fails, apart from complexity and understandability and
>> the option to change preferences between election rounds?
>>
>
> If voters vote exactly the same way in both rounds, and there are three
> candidates, the two-round method is equal to IRV. In this case, it passes
> LNHarm while Condorcet does not.
>
> If the voters don't, then it makes no sense to apply criteria to the
> two-round system as a whole. If you did, you could make the two-round system
> fail Majority unless it had a rule stating that there would be no second
> round in case of a majority preference. Just have a majority vote for A, the
> minority for B, then in the second round, have everybody vote for B.
>
>
>  2) What criteria does the two-round system satisfy that the Contingent
>> vote does not satisfy and vice versa?
>>
>
> See above. One can't apply criteria that applies to a single ballot set to
> a two-round method if the voters change their preferences between the
> rounds. If they don't, then the two-round method is simply the Contingent
> vote and so the compliances must be equal.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.electorama.com/pipermail/election-methods-electorama.com/attachments/20100617/05909d18/attachment-0004.htm>