# In an MMP system, why don't parties game the system by splitting into two parties?

In New Zealand, we have a Mixed Member Proportional system.

Voters have two votes. The electorate vote is used to vote for a candidate to represent their electorate. This vote is determined on a first past the post basis: the candidate with the most electorate votes, for that electorate, gets the electorate seat.

The party vote is a vote for a party and is used to determine the proportional make up of the total seats in parliament. E.g., if a party gets 30% of the party vote, then they should hold 30% of the seats. If less seats were earned through the electorates than the number of seats earned by the party vote, then the difference is made up of list seats.

Example: There are 100 seats in parliament. There are 90 electorates. The Red Party wins 10 electorates, and earns 12% of the party vote. They will be represented in parliament by 10 electorate MPs and 2 list MPs.

There's an additional complication of overhang seats. Overhang seats occur when a party earns more seats through electorates than they do through party votes. In this case, there will be extra seats in parliament.

So for example, if Red Party earns 10 electorate seats but only 5% of the party vote, they will be represented in parliament by 10 electorate MPs and parliament will have 105 members.

The question is – what prevents a party from gaming this overhang dynamic by splitting the party into two, one party to attract party votes and one party to gain electorate votes, and instructing their supporters to vote accordingly?

For example, if the Red Party splits to the Dark Red Party and Light Red Party. The Dark Red Party wins 10 electorate seats and 0% of the party vote, and so is represented by 10 electorate MPs. The Light Red Party wins 0 electorate seats and 10% of the party vote, and so is represented by 10 list MPs. This effectively doubles the party's representation in parliament.

• Great explination of the system, but as discribed it does appear that your recommended strategy would be optimal. Do you know the requirements to establish and maintain a new party? Maybe the Dark or Light party would lose party status under the scheme? Maybe people wouldn't understand or wouldn't agree to such an organized way to "cheat" a system that they value as having integrity? – Dan Aug 5 '14 at 22:29
• @Dan Yeah I suspect that answer is amongst the things you've suggested. A few things: In New Zealand in some cases the major parties do instruct voters in specific electorates to not give their electorate vote to their candidate, but to give it to a supporting minor party's candidate. This is known as a 'cup of tea' deal. stuff.co.nz/national/politics/10320342/… (scroll down to the analysis section). However, it's odd that they major party will still run their own candidate. Perhaps it's a presence thing. – dwjohnston Aug 5 '14 at 22:53
• Also, it's worth mentioning that this taking advantage of overhang only exists in certain versions of MMP, it can be mitigated by giving other parties extra seats to keep the proportions correct (see en.wikipedia.org/wiki/Overhang_seat) – dwjohnston Aug 5 '14 at 22:56
• Here's another reason it doesn't happen: If one party did this, all rival parties would too, negating any benefit but adding a huge cost in terms of bureaucracy. – Cyrus Mar 6 '17 at 14:34
• Germany has this too. And for multiple periods the politicians have been urged to reform the system such that this does not turn out to be so bad. This year we got one of the largest parliaments in the world. But I think that it will only continue because it benefits the parties in power. – Martin Ueding Nov 20 '17 at 8:41

Leaving aside the obvious illegitimacy and dishonesty in this course of action (which would cost some votes and more reputation) and the ability of courts in common law countries to mitigate patent fraud (unless the Crimson and Pink parties actually put forward separate legislative platforms to the voters, rivals could simply bring suit to treat them as the single party they actually are), you're trying to coordinate action among thousands upon thousands of people. That's going to happen in a slipshod fashion that will reduce your theoretical benefits.

More importantly, you're going to have to broadcast this proposal. It's likely to backfire, but let's assume a hyperpartisan society like the USA is becoming where your electorate is mostly on board with anything that sticks it to the satanic Blue Party. Assuming the courts didn't invalidate the game, the Blue Party would just play too, dividing its electorate and party votes in such a way as to double its own representation as well. You've only gained at the expense of the minor third parties, who could splinter in turn, and you've undermined democracy as a means of representing the true will of the people and exposed it as elites playing shuffleboard with the rules.

It's a minor point nationally but one important for the legislators themselves: for no net political benefit, they've just doubled their queues at the capitol lavs and cafeterias and made themselves half as important in their own caucus.

That's not to say there's any reason to change the system. The parties can get away with exploiting your strategy at the margins, when control is closely contested and a major issue is about to be decided. It's in their benefit to leave that option open to themselves, even as they keep an eye on the other guys to make sure they aren't training their constituents to exploit it.

This has actually happened.

Lesotho is one of the four or so countries to use the MMP system. In the 2007 general election, the ruling party voluntarily split in two, fielding only electorate candidates in one party and instructing their followers to vote for the other party for their list vote. They obtained something like 75% of the seats for only 52% of the votes.