[EM] Why I think IRV isn't a serious alternative

[James Gilmour]

> > James Gilmour wrote:
>  > I had always assumed this list was focused so strongly
>  > on single-winner voting systems because there are
>  > so many important single-office (hence single-winner)
>  > elections in the USA.

Bob Richard  > Sent: Tuesday, November 25, 2008 6:19 PM
> That's an important part of the explanation, James, but only one part. 
> Social choice theory, which informs much of the discussion here, isn't 
> directly relevant to PR. The problem to be solved is taken to be making 
> a (single) decision. While forming a legislative body could, in
> principle, be analyzed as making a (single) decision, it rarely is. Even 
> the best examples of the social choice literature tend to relegate PR to 
> a single chapter in a section on miscellaneous topics at the back of the 
> book. See, as just one example, Tideman's "Collective Decisions and 
> Voting", chapter 15.

Bob, thanks, but I thought the chicken and the egg were the other way round here.  I had assumed that those who were concerned about
the defects in single-winner voting systems had looked to social choice for a solution, because, as you say, social choice theory
was developed to address the making of single decisions.  I have not read at all widely in social choice (as my main concern is with
multi-winner elections), but I am aware of its origins in a fusion of sociology and political economy.  I am also aware that some
social choice theorists have turned their attention to voting systems and so probably have a different perspective from those whose
backgrounds were in electoral science.

My background is in neither, but I have suspicion that real electors have different expectations and behave differently when asked
to make a decision and when asked to elect a candidate to represent them.  I suspect they expect to compromise in making a decision
but don't expect to compromise in an election  - that would be my interpretation of the electors' intuitive attachment to "Later no
harm" which I have encountered repeatedly.

With regard to the election of a legislative body, I think it would be wrong to see this as any form of "single decision".  My own
position is that I want to see all significant viewpoints represented with due regard to the practical constraints and the other
expectations the electors have of "representation".  I don't know enough about social choice theory to know whether it could
possibly be generalised to encompass multi-winner elections.  Certainly it would be wrong to make multi-winner elections conform to
some social choice model that was devised for single decision making.

It is. however, interesting that some aspects of the social choice approach are apparent in some of the STV-PR counting rules, as
the newer, "inclusive" rules have the effect of maximising the consensus of representation, whereas the oldest rules have the effect
of maximising the diversity of representation.  The differences in the outcome are, in practice, small, but there is no doubt about
these effects, even though the newer, "inclusive" rules were not developed with the intention of implementing any social choice
approach to representation.

James

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