[EM] Responses to some of Forest's ideas

[LAYTON Craig]

Richard Moore wrote:

> >  9 A>B>C>D=E=F : 100>90>1>0=0=0     : ZI AB  : St AB 
> > 38 B>D>A>C=E=F : 100>52>51>0=0=0    : ZI BDA : St B
>
>I don't see why the second group would truncate to B in the 
>informed vote. Just given the information that clones E and 
>F don't have a chance, a simple informed strategy 
>calculation could be made by removing E and F from the 
>picture and doing a mean utility calculation (203/4 = 50.75)
>and voting BDA. The information that C is a likely front 
>runner would give even more reason to vote BDA.

I guess this shows the difficulty of defining good strategy.  I assumed that
the group would truncate to B given the information that B was a front
runner.  Knowing that A is probably running in third place (directly behind
B) would futher motivate the faction to vote only B.

>Discounting E and F, 255/4 = 63.75, so possible strategic 
>vote is CBA. Depending how confident this group is in the 
>information that D will lose, they might truncate to CB or
>just C, but we don't know for sure. "C only" seems unlikely 
>to me unless these voters are reasonably sure of D's and A's 
>defeats.

You are basically suggesting a slightly enhanced zero info strategy.  It
should be clear from the polls that the front runners are B and C.
Generally, strategy in such a situation is to make your approval cuttoff
point between the two front-runners.

> >  9 D>C>B>A=E=F : 100>10>9>0=0=0     : ZI DC  : St DC
>
>Wrong, ZI vote here is D only (119/6 > 10). Strategic vote 
>could be DC or DCB, depending on how much doubt the 
>pre-election information casts on candidate D. If the 
>information is believed to be unreliable, this group might 
>stick with D only.

Yes, I did make a mistake here (again).  I think that the utilities should
be adjusted (to something like 100>60>10>0..) to make the example work.

>For ZI I get A, also. For NZI, I see B as the most likely 
>winner (since I don't expect to see enough CBA voters 
>dropping B to make C win).
>
>Incidentally, I've long suspected there is (in general) no 
>such thing as universally available "perfect information" in 
>Approval voting. 

If you knew that other voters were rational utility maximisers, perfect
information would be their sincere utilities.  In a real life situation,
detailed polls could be close, if the pollsters ask questions like "if x and
y were the frontrunners, what would be your approval vote?".  Supporters of
particular candidates would probably have similar enough voting patterns or
strategies to enable an accurate prediction.  The problem with polling is
not that it is inaccurate - as a general rule a well designed and adequately
resourced survey is highly accurate - it is that it is constantly out of
date, as voters change their minds.