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

Question

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.

Answer 1

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.

https://fruitsandvotes.wordpress.com/2007/02/23/mmp-manipulated-in-lesotho/

Needless to say, this approach was very badly received in Lesotho. I can't imagine it happening in New Zealand, what with the controversy surrounding ACT's single seat in Epsom.

Answer 2

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.

Answer 3

The Alba Party in Scotland to some extent used this strategy in the 2021 elections to the Scottish Parliament. Elections use an additional member system with separate votes for constituency members and party list members. Constituency members are elected first past the post and party list (regional) members are subsequently allocated so that the overall proportion of members across all parties matches the party list vote as far as possible. In recent previous elections the ruling Scottish National Party had got around 50% of the vote and won almost all constituency seats, but the party list places went to other parties who got no constituency members but a sizable vote on the party list, so that despite being by far the most popular party the SNP were not guaranteed a majority.

Alba was established shortly before the election: many of its members left the SNP to join the new party, and both parties had a common goal of supporting Scottish independence. Alba, and its leader Alex Salmond, argued that due to the PR system, if you voted for SNP in constituencies and Alba in the list, then you would end up with more MSPs who supported independence than if you voted SNP twice. It expressed a strategy of "maximising the vote" for independence by getting votes for pro-independence parties. (The Guardian)

In the event, Alba got a tiny share of vote and gained no members so it was not a success. This wasn't exactly a case of a party splitting purely for electoral reasons, as there were some policy differences (e.g. over timetable for an independence referendum and LGBT rights), and some personal reasons for individuals to quit the SNP. But Alba presented it as an attempt to maximise the vote for independence.

See Wikipedia for more detail: Alba Party, 2021 Scottish Parliament election.