[EM] Summability

Adam Haas Tarr atarr at ecn.purdue.edu
Thu Jul 24 12:47:02 PDT 2003

Kevin wrote and Markus responded:

>> I'm surprised to read this.  I thought "simple strategy" was a
>> virtue for an electoral method.  Surely runtime isn't considered
>> a serious issue for summable methods...?
>No! It is a desirable property that there is no simple way to
>manipulate the result of the elections.

Well, I don't think anybody here would deny that.  But the simple fact 
that one can more easily get a sense of how the polls will translate into 
election results, does not mean that the method is more manipulable in 
reality.  A well-designed Condorcet system may be transparent to the 
voters, but they will have a hard time manipulating it, and will 
generally find an honest ballot to be a good choice.

IRV, on the other hand, will produce fairly chaotic results in close 
races between more than two candidates.  This means voters will be unsure 
what their best strategy is, any may well end up regretting their vote.  
If all the voters had good information, then they would be more likely to 
know when to compromise and when to vote honestly, and the average voter 
would probably be more satisfied with their vote.

So the intractability that comes with IRV does not, in my mind, count as 
a significant advantage.  Denying people their optimal strategies due to 
lack of information does not make better results especially likely when 
the results are chaotic.

Note that I'm not arguing that summability is a crucial criterion - I'm 
just saying that I don't see non-summability as an advantage.  All things 
being equal, I'd choose a summable method, but all things are rarely 


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