[EM] Biproportional representation (was Re: Preferential voting system where a candidate may win multiple seats)

[Juho Laatu]

On 29.7.2013, at 14.36, Kristofer Munsterhjelm wrote:

> On 07/28/2013 04:37 PM, Vidar Wahlberg wrote:

>> - District seats are determined externally and thus not apportioned in
>>   this implementation.
> 
> A similar trick could be used to implement a threshold if desired. It would be complicated, though, something like:
> 
> 1. Do a county-by-county count.
> 2. Parties below the threshold have their number of seats fixed to the number of seats they got "directly".
> 3. Fixing these parties' number of seats, determine the number of seats for the other parties by national Sainte-Laguë: each party gets a seat as in Sainte-Laguë, but when a party below the threshold have got all their seats according to 2., remove that party from the count.
> 4. Use the result as the target for the number of party seats.
> 
> I'd still rather use an absolute but lower threshold, though; or none at all, like you're doing.

Yes, none at all would be best. District based tresholds are not nice since parties whose support is concentrated in one or few districts may get seats, while other parties (of same size) whose support is evenly spread do not get any seats.

> The method itself will partly make votes unequal by weighting them to match the district totals you have already specified. However, it will not be quite as biased as just preweighting all the vote counts, since the party axis is based on the unweighted votes.
> 
> That is, it will give certain districts more than its "fair" share of MPs according to population alone. But it won't give parties disproportionate numbers of MPs like it does districts, because the party target is provided by national Sainte-Laguë.
> 
> That's an interesting tension. To see how it works, consider an extreme: Finnmark gets every seat but one, but the party target is based on a national count. Then almost every MP would come from Finnmark (contrary to relative party support there), but even if most Finnmark voters voted for Rødt, Rødt would still only get two Finnmark MPs.

I guess either voters of other districts will decide which parties will get seats in Finnmark, or alternatively Finnmark voters will have higher weight than others in determining which parties will get seats nationally. The latter case may not be too bad if one thinks that the development of the more complex counting schemes maybe has started from a situation where all districts elected their representatives separetely, but where Finnmark's proportion of seats was higher than its proportion of voters.

Juho