[EM] Query re. Approval voting, July 25

[John B. Hodges]

Greetings.

I'm satisfied that for the task of filling a single seat in a race 
with multiple candidates, Approval voting can perform well, IF the 
voters use good strategy for setting their approval threshold.

Approval voting, in plain English, attempts to find the candidate 
that the greatest number of voters regard as not unacceptable. This 
is a very modest ambition. One criticism of AV is that it can favor 
mediocrity. For example in a four-candidate race, if all voters 
approve their top three, the winner may be someone ranked second or 
third by a great majority. (If they vote for "anybody but Hanson", 
they may get exactly that.) Arguably this is not a disaster- "hey, 
you marked the ballots"- AV never claims to pick the best, only the 
most-widely-acceptable. But it is still a drawback, compared to other 
voting systems that seek, by some definition, to pick the "best" 
candidate. 

There are strategies for setting your approval threshold higher, that 
analytically give better results. If you know enough about the 
candidates to judge how well you like them, but nothing else, then 
approve the "best half", the candidates that are "better than the 
average candidate". If pollsters have made it clear that some are 
running well ahead of others, approve whichever of the front-runners 
you like best, plus anyone else that you like better. These 
strategies are not hard.

My question is about the secondary consequences of the second 
strategy, "favorite front-runner plus". If a widely-believed poll, 
reporting that candidate B is a front-runner, leads to many people 
giving approval votes to B, then there is serious incentive to 
falsify polls. Those supporting B would want to have polls saying B 
was running ahead, those opposing B would want polls saying B was 
runnng behind.

More technically, if the outcome of an election by Approval voting 
depends strongly (or entirely) on the strategy the voters adopt re. 
where to put their approval threshold, and they are sophisticated 
enough to try to put it at the "expected value of the election", then 
there is strong incentive for campaigners to try to manipulate the 
voter's expectations.

In that environment, it may become difficult for the voters to know 
which polls are reliable. They can always choose to ignore all the 
polls and fall back on the "best half" strategy. Then the only 
problem they have is forming an informed opinion of the merits of the 
candidates, which is a problem with many voting rules.

So my question is this: how is Approval voting expected to perform in 
a setting of "propaganda overload", with lots of info of all types 
available but much of it false or shaded, and where there is much 
voter distrust of it all?

-- 
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John B. Hodges, jbhodges@    @usit.net

"The secret of the demagogue is to make himself as stupid as
  his audience so that they believe they are as clever as he."
    -- Karl Kraus