[EM] Margins vs. Winning Votes

[Dave Ketchum]

On Mon, 25 Jul 2005 10:53:52 +0300 Juho Laatu wrote:

> On Jul 25, 2005, at 01:24, Dave Ketchum wrote:
> 
>> "Strategically" still turns me off.  Voters who preferred B over A, 
>> and had planned to vote accordingly, are gambling that they can get 
>> better results by claiming, instead, to prefer A over B:
>>      In some cases they can, unfortunately, succeed at what they claim 
>> to want.
>>      If these can change their votes, then so can others for other 
>> reasons, thus destroying the knowledge all used in plotting.
>>      How cycles operate was used in the plotting.  Cycles are valuable 
>> in resolving near ties, but deliberately setting them up for intended 
>> results is tricky.
> 
> 
> My thoughts around the pair-wise comparison based voting methods and 
> strategies are roughly as follows. Rating based methods are maybe too 
> vulnerable to strategies in contentious elections, so we may have to 
> satisfy with ranking based methods. Pair-wise comparison methods are a 
> wonderful solution that allows voters to express their preferences quite 
> extensively (but still easily) and in most cases without any strategy 
> problems. Sincere voting thus seems to pay off (better than in many 
> currently used election methods). Unfortunately we have the cycle 
> related problems (otherwise the methods would be quite flawless). 
> Natural cycles are luckily quite rare. Artificially generated cycles are 
> a bigger problem. The big question is if pair-wise methods are still 
> good enough to be recommended for use. I think the differences between 
> different tie breaking methods are not that big. Since all of the 
> pair-wise comparison methods have some of the basic vulnerabilities, the 
> more important question seems to be if the pair-wise comparison methods 
> are useful in general as a group. In real election situation also the 
> real life environment has an influence. If majority of the voters vote 
> sincerely, the strategic voting problem remains just as background noise 
> in the process without causing any considerable harm (((hmm, the example 
> I presented studied the the possibility that very few strategic votes 
> could pick a "bad winner"...))). If the method and attitudes of voters 
> are bad enough, then strategic voting might be a problem. And if the 
> impact of strategic voting would be worse than what currently used 
> election methods have (e.g. some really bad candidates would be 
> elected), then we would need to deem pair-wise election methods unusable 
> (is some environments?) and would be forced to go back to (recommending) 
> some simpler election methods (e.g. IRV, two round runoff, plurality, 
> approval). So far I'm leaning in the direction that strategic voting 
> would at least in large public elections be marginal (or done mostly by 
> voters who didn't know that in the new method they don't need to vote 
> strategically but the a sincere vote is likely to defend their interests 
> in the best possible way). I'm also leaning in the direction that voting 
> methods that pick the best winner could be more useful than ones that 
> aim at eliminating strategies. Partly because people want the method to 
> provide best possible results, partly because the strategic fixes may be 
> marginal, partly to keep the method simple and understandable, and 
> partly because strategic countermeasures easily lead people to thinking 
> that strategic voting is a key property of the method. I'm not 100% sure 
> that the simplest methods work fine and I'm still waiting for someone to 
> prove that some methods are unusable and some usable (but haven't seen 
> (or understood :-) that yet). So, for me the question is if the basic 
> pair-wise comparison methods are strategy free enough to be used as 
> practical election methods as they are. And my guess is, yes they are in 
> most single winner elections.


My belief is that possibilities of strategy are best ignored, other than 
preventing those who would try from having information to make them 
successful.

Strategy needs both knowledge of expected results without strategy, and 
cooperation among enough voters to make a difference.  Assuming there is 
such a group for an election, there is almost certainly room for others to 
have the same vote count information, know of the first group's plotting, 
and do their own plot that destroys usability of the information for the 
first group.

My comparison of methods:
      Condorcet wv - comparing pairs, we are looking for the most popular 
candidate.  When we have a near tie we call it a cycle - perhaps we could 
do a runoff, but we mostly need resolution of the near tie, and all that 
is needed is to break that neatly.
      Condorcet margins - like above, but less apt to pick best liked.
      IRV - same ballot and, almost always, same winner as above. 
Sometimes fact that IRV is willing to decide without looking at whole 
ballots gets bad results.
      Two round runoff - expensive and, too often, best liked candidate 
does not get to the runoff.
      Plurality - the one thinkers want to escape.
      Approval - its backers like to brag, but it is not that simple - 
unlike Condorcet and IRV, voters CANNOT say:  I prefer Nader but, only if 
I cannot have Nader, give me Kerry as better than Bush.
      Ratings - I choke on the complexity as worse than the above.

> 
>> But here the example you constructed resulted in a win by the plotters 
>> in wv - and in the result they claimed to want, but which was worse 
>> for them than what they would have achieved without plotting, under 
>> margins.
> 
> 
> Yes, based on this single isolated example one should recommend margins 
> based methods and not winning votes based methods. I in general do like 
> margins also since they seem to be a more natural measure of preference 
> than winning votes, so this result is just fine for me :-). Winning 
> votes have maybe some burden of being overloaded with hopes of finding a 
> panacea in the fight against strategic voting.


I do not see how this example promotes margins:
      Under wv the plotters achieved their goals.  NOT that I approve, for 
they were only guessing as to what other voters might do.
      Under margins they claimed to prefer the LEAST liked candidate over 
one they actually preferred.  Fact that their strategy elected the least 
liked is not a success to celebrate - more a warning to be cautious when 
considering strategy.

> 
> Best Regards,
> Juho

-- 
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  Dave Ketchum   108 Halstead Ave, Owego, NY  13827-1708   607-687-5026
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