[EM] Re: IMHO, IRV superior to Approval

[Chris Benham]

Kevin,
You wrote (Sun.Jun.6):

>Mutual Majority and Clone Independence are easy to meet, but they also don't
>guarantee much.  Clones, and a majority-strength coalition for a set of more
>than one candidate, hardly ever exist.  I would love to see a real IRV election
>where they did.
>
Where did you get that idea?  It happens all the time in Australia. The 
Federal  government here is based on two conservative
parties in coalition, which are permanent allies. In some seats they 
each field a candidate, and in those seats they tightly "exchange
preferences".  In some of those seats one of them wins with the help of 
the second preferences of the other, and so together  they
make a "majority strength coalition". Decades ago, there was a small 
right-wing Catholic (Democratic Labour Party) party that kept the 
Coalition in power by always giving them their second preferences, and I 
assume the favour was returned. In those seats where the big 
conservative party won with DLP preferences, I suppose that was another 
 "majority strength coalition".  In fact I believe that IRV
was first introduced so the originally trade-union based Labor Party, 
which was disciplined and fielded one candidate per seat, wouldn't
beat a larger number of  conservative candidates, who presumably in some 
seats were a  majority strength anti-Labor Party coalition.


>This is a tired scenario, but consider this while thinking of "half-clones":
>40 A
>35 C>B
>25 B
>
>I call {BC} a half-clone set.  In Approval the C>B voters can vote CB and still get
>B to win, and this doesn't involve any insincerity.  In IRV those voters should put
>C below B in order to avoid electing A.  Not only does IRV encourage insincere
>voting here, but the fact that it does so will be a strong incentive for C not to
>enter the race at all.
>
>So the biggest reason I prefer Approval to IRV is IRV's nomination disincentives.
>
I find it a bit implausible that the C voters all give their second 
-preferences to B, with no recipricocity  at all. If  A, B, and C
were the endorsed candidates of rival establised political parties  for 
a seat in Parliament in  Australia , then  it would never occur
to C to not run. The same would apply to the parliaments of many other 
countries, if they were to use IRV (like the UK, New Zealand
and France, and other European countries.)

>> I  like methods that have no zero- information strategy, 
>
>I think you are saying Approval has strategy, even with zero-info, because sincere
>voting is undefined for Approval.
>
>> and  doesn't 
>> reward  indecisive voters by giving them extra clout.  If  voter  A
>> ranks candidate X last,  and  because of  prejudice, ignorance and 
>> stupidity has no ranking of the other candidates; and voter B ranks
>> candidate Y last but also strictly ranks all the other candidates; then 
>> both candidates X and Y should have the same probabilty of being
>> elected.
>
>I still think "probability of being elected" is undefined here.  Usually that
>term is used when there is a tie...
>
By "probabilty of being elected", I meant exactly that. To make it 
clearer, instead of referring to two individual voters, I could
instead have said that there are two equal-sized factions of voters.

>> "No Zero-Information Strategy"  also implies that Later-no-harm and 
>>  Later-no-help should be in balance. That is, that the chances of
>> harming or helping an already ranked candidate by ranking another below, 
>> should be the same.
>
>1. Can you tell me a method besides Approval which fails "no zero-info strategy"?
>Because I take it you really mean that zero-info strategy should be equivalent to
>a sincere vote.
>2. Can you tell me a method which fails "no zero-info strategy" where LNHarm and
>LNHelp are not in balance?
>
Yes and Yes. A method that simply asks the voters to rank the 
candidates, but  gives voters who do anything else (based on their
ratings) a better expectation, fails "No Zero-Info Strategy".  I gather 
from posts in the archives, that Condorcet (Winning Votes) fails
because if voters have a sufficiently large gap in their ratings, say 
between second and third place, they do better to insincerely rank
the candidates above the gap in equal-first place. Also, it is true, or 
has been strongly conjectured, that voters who do not have a sincere
full ranking do better to strictly rank all the candidates below 
first-place .
Bucklin, Weighted  Median Approval, the Woodall methods Quota-Limited 
Trickle-Down  and Descending Acquiescing Coalitions all
fail Later-no-harm , but meet Later-no-help.  That means that truncation 
is a big implicit  approval-cutoff, and if voters have a big gap
in their ratings they would do better to insincerely not rank the 
candidates below it.
On the other hand, the Woodall  set-intersection method Descending Solid 
Coalitions meets Later-no-harm but fails Later-no-help.
That means that the voter definitely does better to "random-fill", ie if 
the voter does not have a full ranking, s/he should strictly rank
all the bottom candidates at random.

>> And of course voters who succeed in ignoring this circus and instead just concentrate on the 
>> policies and qualities of the candidates, will potentially be greatly disadvantaged (much more
>> than a "naive", sincere IRV voter).
>
>Here I completely disagree.  A gut-sentiment Approval voter will probably not be far off
>from his optimal way of voting.  He screws up only if he approves or disapproves both of
>the strongest candidates.  In IRV he can screw up by not guessing who needed his traveling
>vote when.
>
I don't see why the it is particularly unlikely that the 
"zero-information"  (poll-ignoring) voter wouldn't distinguish between 
the two
leading candidates (not approving either or approving both). In my 
opinion, the concientious voter shouldn't have to do anything
except calmly and rationally rank the candidates.

Chris Benham

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