# 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.

I will note that in New Zealand gaming like this does happen to a limited extent - where the major parties may instruct voters in a particular electorate to give their electorate vote to a candidate from a minor party, who will often be the only person from that party represented in parliament. This is known as a 'cup of tea' deal - you can see details about when this has occurred here. Though what I'll note is that it's not as straight forward as just creating an overhang seat - New Zealand also has a complication where party vote thresholds are not required if you have an electorate member.

• 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. 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) 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. 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. Nov 20 '17 at 8:41

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.