[Election-Methods] MCA's IIB problem fixed

Kevin Venzke stepjak at yahoo.fr
Mon Jan 28 11:53:09 PST 2008


--- Kevin Venzke <KVenzke at markjamesassociates.com> a écrit :
> Kevin,
> Kevin Venzke wrote:
> As far as my strategy simulation is concerned, this rule change raises
> the
> question of how voters should evaluate the possibility that they elevate
> a
> candidate to the top spot on first preferences only to see him lose due
> to
> pairwise opposition.
Chris replies:
> I don't fully understand this point.  Any candidate who would win in the
> first round of regular  MCA would 
> also win in the first round of  my suggested version, and in both the FPW
>  can win in the second round.
> The only difference is that my version is more likely to have a
> first-round winner, which I suppose in the
> FBC-complying 3-slot ballot version might be a bit self-defeating.  In
> your  FPP-approval ballot version
> I don't see how it greatly complicates the strategy.

Currently the value of a first-preference vote for A is estimated as the
likelihood that A can achieve majority times the likelihood that no
candidate will achieve majority (e.g. if a majority is guaranteed then no
vote is of value) times the difference between A's utility and your
expectation should the election be resolved on approval.

With your rule you no longer simply break ties between one candidate's
majority and "no majority"; you have to compare against each other
candidate FPP-style. And you can't simply compare the candidate's utility
to the approval expectation, because the candidate could lose despite
coming in first.

If I were implementing this method I would probably have voters keep track
of their expectation when each candidate is the TRW but has too high
pairwise opposition. This kind of approach so far has produced a lot of
intelligent behavior. It has a couple of downsides though: 1. Voters can't
predict the value of situations which weren't observed to occur in the
polls, and thus won't try to create them, and 2. There seem to be a number
of "cum hoc ergo propter hoc" mistakes where voters vote for situations
that have coincided with outcomes they liked, but which didn't necessarily
cause them.

Kevin Venzke

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