[Election-Methods] STV in the context of modeling voters

James Gilmour jgilmour at globalnet.co.uk
Sun Dec 30 11:57:36 PST 2007

Jonathan Lundell > Sent: 30 December 2007 18:55
> > On Dec 30, 2007, at 2:14 AM, Dan Bishop wrote:
> > In the coming weeks/months/whenever-I-feel-like-it, I will be performing
> > simulations to evaluate the performance of multi-winner methods.  In
> > order to do this, I will make the assumptions that:
> >
> > * There is a uniform linear political spectrum.  (Other models of voter
> > behavior will be considered later.)
> > * Candidates are uniformly-distributed random variables in.
> > * All votes are sincere.  (i.e., a voter at position V votes A>B iff
> > abs(A-V) < abs(B-V))
> >
> > The last two assumptions, that no strategy is involved in either 
> > nominations or voting, is admittedly unrealistic.  But, as I see it, in
> > order to know the best strategy to use with a method, you must first
> > know how it would behave without strategy, so that's a useful thing to
> > analyze.
> The first assumption is pretty unrealistic as well. I look forward to  
> seeing your other voter models.
> For example, I was thinking of the problem faced by US Democratic  
> primary voters during the current cycle. Granted, they don't have to  
> rank the candidates (except in Iowa, where there's a limited  
> contingency process), but they still have to come up with a first  
> choice.
> Looking at the candidates, though, it seems to me not terribly useful  
> to try to order them in any one dimension, and to the extent that they  
> can be ordered on multiple dimensions, very difficult to resolve those  
> rankings in to a single ordering (or a first choice).
> Many voters appear to value "electability", for example. But we're  
> faced with the difficulty not only of trying to rank (and perhaps  
> weight) electability, but then to figure out how that weighting  
> figures into some larger process that looks at how effective the  
> candidate might be if elected, how we feel about their stands on  
> various issues (Iraq, health care, etc). Then there are second-  
> (third-?) order considerations. I may think that Iraq is a more  
> important issue than health care, but question the extent to which any  
> particular candidate, however much I might identify with their  
> position, can do about it. So maybe I should weight health care plans  
> more heavily, if I think that we're "ready" for serious reform.
> And so on.
> I tentatively conclude that it's not very helpful to model that kind  
> of decision process, partly because it's impossibly difficult to model  
> and, more important, to validate the model.
> And here's where Gilmour's 'contingency' becomes especially relevant.  

The reality of "contingency choices" in voting systems like IRV and STV-PR was recognised long before Gilmour became a student of
voting systems, but I am glad this reality is recognised by some others.

> Voters aren't dispassionate computers with elaborate linear  
> programming built in. What they *can* do (we know because they  
> actually *do* it) is to decide, finally, on their first choice. And  
> having accepted that, it's no great leap to assume that they can  
> decide on a second choice contingent on the unavailability, for  
> whatever reason, of their first choice.

Those who wish to model such decision-making by voters must also recognise that two voters who come to the same conclusion (e.g.
same first and second preferences) will very likely have reached their identical conclusions by consideration of completely
different sets of factors with the candidates scattered in different positions along the very different sets of dimensions.  I
suspect it will be quite difficult to model how several thousands of different n-dimensional spaces can all be collapsed into
one-dimension to order the one set of candidates, but that's what millions and millions of real voters do in public elections
(although I am sure they don't express it in those terms!).

> I'll try not to turn this into a pitch for STV, but it strikes me that  
> one of its attractions may be that with its explicit reliance on  
> contingent choices, it asks voters to solve a problem they're prepared  
> to deal with, without solving impossible resolutions of conflicting-- 
> and vague--personal value scales.

It is important to recognise that the context for "solving this problem" is quite different in IRV and STV-PR and I suspect that may
influence how each voter "solves" the problem in the two very different situations.  In any single-winner election only the one
"majority" opinion group can secure direct representation (though how that "majority" group is identified will vary according to the
voting system, e.g. IRV, Condorcet, Borda, Approval, Range)   In a multi-winner election several different, and perhaps very
disparate, opinion groups can each secure direct representation simultaneously, IF that is what the voters want.  That (I think)
makes "solving the problem" much easier from the individual voter's perspective.

> As a voter, I prefer to think in terms of contingent choices. I don't  
> *want* to solve the strategy problem presented by approval voting.  
> With range voting, I don't feel that I'm in a position to assign  
> cardinal weightings to the candidates (never mind for the moment how  
> they're ultimately counted), nor do I want to be burdened with then  
> turning those numbers into a strategic game to maximize my outcome.
> Sure, STV is manipulable. But so is everything else. And its implicit  
> decision model conforms to something that I, as a voter, can make  
> sense of. And in making my contingent choices, STV's later-no-harm  
> property becomes important to me. Of course I'd like it to be  
> monotonic, etc, but on *my* value scale, its advantages, in practice,  
> outweigh its shortcomings--in practice.

I agree with Jonathan here, as I also attach great importance to "later-no-harm" and this seems to be an important criterion for UK
electors more generally.  Non-monotonicity is certainly a defect in STV-PR, but it is one that can be ignored for public elections
with thousands, tens-of-thousands or hundreds-of-thousands of voters because neither the voters nor the candidates can exploit it.
Unfortunately we cannot secure monotonicity in STV-PR without sacrificing "later-no-harm", and "later-no-harm" is much, much more
important, though I accept that opinions may well differ on that assessment.

James Gilmour

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