Sunday, April 25, 2010

MMP Made Easy

Scottish, Welsh, German and New Zealand Parliamentary elections use a type of Proportional Representation called the Mixed Member Proportional system (MMP).

The ten-second definition of MMP is this:


MMP is a voting system which mixes our winner-take-all system with an element of proportional representation, so that the number of MPs elected to Parliament from each province matches the share of the overall votes cast by supporters of each party in that province.

Different places use different MMP models. This is a description of an MMP model with “open lists.”

Each voter has two votes.

The local vote is used to elect an MP to represent your riding, as today.

The regional vote or party vote is used to elect several regional MPs from your region.




If a party’s voters have managed to elect only a few local MPs in that region, or none at all, that party gets additional “top-up” seats to make their final total more in line with their vote share in the "top-up" region.

The party’s regional candidates with the most votes win those seats. That’s why it’s called “open list.”


Your local ballot will look like today's ballot. Your second ballot -- the regional ballot --will look like the right-hand part of this ballot.

Here are further details on this model as designed by the Law Commission of Canada.

What would the 2011 election results have been under this model?

(The number of regional MPs you have depends on the size of your "top-up" region: if they are medium-sized regions it might be five, maybe as many as eight or more. In smaller provinces, the "top-up region" would be the whole province.)


MooMoo said...

Hi Wilf,

In the ballot in your blog there is ranking on the local side and an open list prop system on the regional side. Is this an example of MMP? Would this system work and make the AV libs happy, but give us proportional representation as well?

Wilf Day said...

Yes, that was the MMP model recommended for the UK by the Jenkins Commission, which Labour promised to pursue in in its 2011 election manifesto. No action. Although no actual working MMP model uses a preferential ballot to elect local MPs, it would certainly be a workable MMP model. The downside is that it would introduce an even more complex ballot to little purpose since the local MP with a preferential ballot would, in the vast majority of ridings, be the same either way. Liberals would gain a few and lose a few, but if they want, it could certainly be one of the models on the table.