[EM] STV and Trees

[Juho]

On Aug 22, 2008, at 2:18 , Raph Frank wrote:

> On Thu, Aug 21, 2008 at 11:30 PM, Juho <juho4880 at yahoo.co.uk> wrote:
>> Yes, this is where I see that STV and trees (or lists) can be  
>> combined in a
>> fruitful way. If the number of candidates is large then short  
>> votes may lead
>> to problems in STV. To guarantee proper inheritance of the votes  
>> it would be
>> useful to direct the voting power of short votes to some branch of  
>> the tree.
>> A bullet vote to some candidate would automatically be counted for  
>> the local
>> group of this candidate and for the mother party too. Longer votes  
>> could be
>> counted e.g. for the group and party of the last listed candidate by
>> default. (There are also other alternative approaches but trees  
>> seem most
>> natural to me.)
>
> Also, trees and candidate lists can be considered somewhat equivalent.

Yes, trees just add some more information when compared to lists. The  
basic philosophy of trees is that when the voter stops giving  
preferences we can continue with candidate given preferences. Tree is  
not as detailed as a candidate given full preference order of all  
candidates (or many of them) would be but it is accurate enough,  
readable with one quick look (no need to wade through numerous  
slightly differing orders), can not be used easily to misguide the  
voter (Fiji case), is probably agreeable to most voters of the  
candidate (does not state the preference order within the nearest  
group etc.), guarantees that votes are not lost (votes contribute to  
PR at group and party levels), gives a clear structure to the  
political field, and binds the candidates clearly to the values that  
they indicate to represent.

Alternatives to tree based inheritance include candidate given  
preference order, party given preference order, third 'party' given  
preference order, party list, list of opinions that a candidate  
supports (=multi-dimensional), mandatory full ranking, short votes  
(tails easily lost), limited number of candidates, delegable proxy /  
cascade style trees.

> Thus, I don't see them as massively different ... the trees just  
> add more
> structure and reduce the freedom.

The intention was not to reduce freedom. If a voter wants to bypass  
the default inheritance order as given in the tree he just ranks all  
the candidates (also other tools like names of some groups could be  
available if we want to go for maximum flexibility, e.g. "women",  
"Dublin", "under 30", "those who voted yes for X", "candidates that  
support Y"). Also declaring a vote to be just as written is ok (no  
inheritance if candidates on the ballot run out).

> If you have a tree, you can form a candidate list by ordering
>
> 1) Candidate himself
> 2) all members of the same leaf
> 3) all members of the next branch + other leaves
> (etc).
>
> This ranking of all the candidates would then be the candidate's list.
>
> Ofc, it requires that the candidate list allows equal rankings.

Yes, this leads to STV votes that support equalities. Bullet vote to  
C1 could become in effect C1>G1=G2=G3>P1=P2=P3=...

> This is not allowed under standard PR-STV, but isn't that big an
> issue.  There are a few different ways to allow it.   (The easiest
> might just to be allow tha candidate to decide how to break ties).
>
> It becomes about balancing flexibility and simplifying info for the  
> voter.

Yes, except that I think no flexibility is lost, so on the "negative"  
side there is only the added information in the poster listing all  
the candidates and that the voters are expected to roughly understand  
(well, it is maybe much easier to understand that than trying to dig  
out the opinions and more detailed affiliations of all the potential  
candidates oneself).

> Perhaps, since they are only for a small fraction of each vote,
> the reduced load on the voter of trees would be better.

Bullet voting could be common if the tree is informative enough.  
Also, in elections with multiple candidates the lost fractions could  
be relatively large.

> (Though, I would
> allow a candidate to opt out).

It probably is possible for a candidate to establish one's own party  
and not contribute and not benefit of the votes given to the party  
(or group). In most cases I'd expect the candidates to benefit of  
being a member of a party/group (even if the algorithm wouldn't  
favour large groupings like e.g. d'Hondt).

> A candidate might be shown as
>
> Name (Party/Wing)
> if he is part of the party's tree system
>
> or
>
> Name (Party/Unaligned)
> if they use the custom list.

Yes. In this case the candidate seems to be a member of the party  
(that is a group too) but not a member of any subgroup. This case  
must be covered in the election rules or in the party internal rules  
since it is quite natural that some candidates do not fit in any of  
the established subgroups.

Candidates that are not members of any subgroups (at some level in  
the tree) could be grouped together to form a default list (unless  
they object this too). The reason I'm interested in this particular  
case is that when some group, e.g. the left wing of a party, forms a  
subgroup it is often natural to see the remaining candidates as the  
right wing, and maybe the votes of those candidates should be summed  
up since otherwise the left wing may be in a better position. Well,  
maybe we just automatically give the "non left wingers" an option to  
form a corresponding grouping when we learn that a left wing grouping  
has been formed (and candidates may opt in and opt out).

> The only rule would be that they must rank all party members before  
> any other
> candidate.  (Though I think parties will insist on that anyway, in
> order to be allowed
> use the party's brand.)

I didn't quite understand what the alternative to this would be. I  
think the basic tree structure automatically cuts out any horizontal  
inheritance to other parties (in the default inheritance order). If a  
candidate chooses to become a candidate of a rural branch of a green  
branch of a conservative party of a right wing coalition then he is  
simply bound to all those levels (and that order ("rural green"  
instead of "green rural")).

Juho





	
	
		
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