Alex asked: > Or, what is the typical > district size in places that use STV-PR for public elections?
I provided some answers to that question last night. So now to the more general questions. > How many members should a typical legislative district elect? > So what district size would you recommend? There is no "typical" (or "correct") number of members that a legislative district should elect. It is all a matter of trade-offs among factors that pull in opposite directions. The greater the number of members elected together, the more proportional the result will be. But proportionality is not the only factor in representation in the real world. It is certainly not the only factor of concern to real electors. If a town council has 12 members, it is quite practical and acceptable to elect all 12 by STV-PR from a single, town-wide district (US terminology), as the examples from Ireland show. But if we are looking at a national parliament of, say, 120 members, it would be undesirable to elect all 120 from a single national-district. The principal reason is not one of practicality, but rather political consequence. Experience has shown that it is politically undesirable to give representation down to 1 in 120, as the example of the Israel Knesset shows. In countries using party list systems of PR with national aggregation of votes to determine the parties' shares of seats, it is common to apply an arbitrary threshold (typically 5%) specifically to exclude small parties. These thresholds are arbitrary (Why 5%? Why not 4% or 6%?); it would be more logical to accept the de facto thresholds that come with districts - where the sizes of the districts have been determined for other, logical reasons. For this reason I would reject all "extensions" of STV-PR that seek to add any aggregation of votes across districts with the aim of "improving" the PR. Such aggregation is undesirable, flies in the face of the local candidate-based nature of STV-PR, and as experience has shown, is unnecessary to obtain an acceptable result. The law of diminishing returns applies to representation in much the same way as it applies to many other things. As the number of members per district rises, the proportion of voters NOT guaranteed representation falls off very rapidly at first and then progressively more slowly. (This applies to all systems of PR, not just STV-PR.) So there is a trade-off between the proportion of voters not guaranteed representation and the political consequences of giving representation to ever smaller groups with ever decreasing support among the electorate. Of course there will be debate about where along the curve of diminishing returns the district size should be set. One special problem in addressing this question for STV-PR is that many analysts look only at the number of seats a party will be guaranteed for a specified proportion of the first preference votes. They ignore completely the effects of vote transfers. They argue for large district magnitudes to ensure fair representation of the smaller parties. But small parties that cannot muster, say, one-sixth of the first preference votes in a 5-member district frequently win one seat in such districts. There are many examples of this in the results from the STV-PR elections in the Republic of Ireland (since 1920) and in Northern Ireland (since 1973). There is also a trade-off between the proportionality of representation and the localness of representation. These two factors pull strongly in opposite directions so far as optimal district size is concerned. In some political cultures, real electors attach great importance to localness and so it cannot not be ignored. This is certainly true in the UK and in New Zealand. It is much less important in most of continental Europe. I would guess it could be an important factor in the USA and in Canada, but I have no first hand experience on which to base a firm opinion. Proponents of so-called "pure PR" may say that the electors have got their priorities wrong, but practical reformers would be unwise to ignore the electors' desire to secure discrete representation for the "natural communities" that exist within the boundaries of legislatures at all levels. It is to give expression to these natural communities that it is also common to vary the district magnitude among the districts within a legislature. PR purists may protest that this introduces urban/rural bias, and party bias where the support for parties varies from district to district. But experience shows that real electors are more concerned about their communities than about the exactitude of proportional representation. Thus the legislation for local Councils in Northern Ireland stated that districts should elect not fewer than four members and not more than eight, and that five, six or seven should be regarded as the desirable number of members per district. In the STV-PR elections to the Scottish Education Authorities in the 1920s there was even greater diversity, from 3 members to 10 members, and there was great variation within individual Authority areas, e.g. Fife with seven electoral districts of six different sizes: 9, 8, 8, 7, 5, 4, 3. Pragmatic flexibility in practice. James ---- Election-methods mailing list - see http://electorama.com/em for list info
