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Voting matters - To advance the understanding of preferential voting systems

Issue 24, October 2007

(Complete issue in PDF, 496Kb.)

Review

The McDougall Trustees recently asked a senior academic is undertake a review of Voting matters, partly due to some comments on the Internet. You may have noticed a difference to the front sheet since the subtitle has been changed from the previous text: for the technical issues of STV. This change reflects the actual content which is not restricted to STV.

An issue which arose from the review was a criticism of the paper by Allard in Issue 5 which gives a low figure for the number of STV elections which are non-monotonic. It is perhaps not obvious that an election can fail to be monotonic in two distinct ways. Given an election for three seats and six candidates in which A, B and C are elected and X, Y and Z fail to be elected, then increased support for C could result in C not being elected; or alternatively, reduced support for X could result in X being elected. It seems clear that a more robust estimate for the occurrence of a non-monotonic election is needed. An academic has agreed to investigate this. It would also be interesting to know if the actual STV counting rule had an impact on this issue.

Editorial

There are 4 papers in this issue, all of which are comments or reviews of other work:

I D Hill: STV in Northern Ireland and proportional representation
This paper makes two suggestions for increasing the degree of proportionality for elections. Changing the number of seats per constituency would require a legislative change, but is conceptually simple. Using the eligible votes to determine the split is more radical, but why not? What do readers think of this?
Jonathan Lundell and I D Hill: Notes on the Droop quota
The Droop quota is a key issue of STV. Note that the authors place great emphasis on DPC (see the paper for details). This criterion could be regarded as critical for STV, yet some counting methods fail this test, at least in marginal situations.
H R Droop: On Methods of Electing Representatives
In preparing the previous paper, it was clear that the original paper of Droop was not widely available. Hence it was decided to reprint it, with the approval of the original publisher (although long out of copyright). Although long by modern standards, it raises very many issues, the majority of which are still outstanding today. Thanks to the two previous authors and David Farrell in assisting with this reprinting.
E Stensholt: Review - Elections in split societies
This is a review of a book edited by Peter Emerson. The topic of the book is voting systems based upon Borda scores. Such systems are clearly related to STV in many respects and hence a comparison is surely of interest. In order to present the review, a scheme for illustrating voting profiles is used. Note that the review and the book takes into account the political position of a divided society in Northern Ireland.

The Editor must correct a statement made in the last editorial which stated: In electoral terms, Meek has the advantage that the intervention of a no-hope candidate cannot change the choice of the elected candidates - a failing of all the rules used for current hand-counting STV methods. This is not correct in general. For instance, if a Meek count excludes candidates A, B and C (in that order), then rerunning the count without A will get the same result, and also without A and B, or A, B and C. However, a different result may be obtained by excluding B (without A), or by excluding A and C without B, etc. With a conventional count, if the first stage excludes a candidate, then rerunning the count without that candidate does not necessarily obtain the same result.

Readers are no doubt familiar with the problems that were encountered with the Scottish elections this spring. However, the STV elections went off smoothly. The Glasgow election area provided complete details of the voting profiles on the Internet, although it was the only area to do so. This provides a very significant addition to the STV data available for academic study.

The site www.votingmatters.org.uk is now working on the Internet, but bookmarks to the old site should be changed to the new one, since the old site will be removed eventually.

Readers are reminded that views expressed in Voting matters by contributors do not necessarily reflect those of the McDougall Trust or its trustees.

Papers with citations

David Hill: STV in Northern Ireland. (p1-2, PDF 92Kb)
Jonathan Lundell and I D Hill: Notes on the Droop quota. (p3-6, PDF 200Kb)
H R Droop: On Methods of Electing Representatives. (p7-46, PDF 1.1Mbb)
E Stensholt: Review Ñ Elections in split societies. (p47-56, PDF 396Kb)

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