[EM] Unranked ballot election challenge

[Forest Simmons]

Tom, in your example below you keep switching between 546 and 526 for the
size of the A + C faction. (It doesn't make any difference in the winners
by the two methods.)

Here's my two cent's worth:

I don't think that the same population of voters would have voted the same
on their ballots under the two different methods.

If the Approval voters had known that their ballots were to be counted
Unranked IRV style, and also had fairly accurate information about the
size of the various factions, then (most of) the B+C and A+C factions
would have dumped C to have more influence on the outcome between the
perceived frontrunners A and B.

Many of these would have been dumping their favorite.

Unranked IRV fails FBC.

Unranked IRV might work as well as Approval with zero information, but in
the real world it would still suffer from the spoiler / lesser evil
problem. 

Forest

-----------------------------
Tom Ruen wrote ...

Comparing Unranked-IRV with Approval, these methods have divergent winners
in less than 2% of random elections with 3 candidates and many voters. This
is a very small variation, but worthy to be considered.

Here's one (random) election I picked to demonstrate:

Approval ballots:
C=7886 (32.0%)
B=7411 (30.1%)
A=7298 (29.6%)
A+B=1103 (4.5%)
A+C=546 (2.2%)
B+C=405 (1.6%)

Looking at these ballots we can see a very close 3 way race among 3
candidates. We can see C has the largest united coalition and A and B have
the largest compromise coalition.

If we measure by approval:
A=7298+1103+526=8927  (36.2%) (First)
B=7411+1103+405=8919  (36.2%) (Second)
C=7886+405+526=8817    (35.8%) (Third)
A wins by a hair over B.

IRV gives a different result:
Round 1:
A=7886+(1103+546)/2=8112.5 (32.9%) (Third)
B=7411+(1103+405)/2=8165.0 (33.2%) (Second)
C=7886+(405+526)/2=8351.5 (33.9%) (First)
Eliminate A
Round 2:
B=7411+1103+405/2=8716.5 (35.4%) (First)
C=7886+405/2+526=8614.5 (35.0%) (Second)
NOTA=7886 (29.6%) (Third)
B wins

Well, so here we have a case to consider. B has more core supporters than A,
and A has more compromise supporters from C. Splitting votes compared to
full votes makes a difference.

Which result more accurately represents voter preference?

Tom Ruen