Time to take a look at the Mixed-member proportional representation system, a family of electoral systems increasingly gaining appeal among electoral reform advocates in the United States. Originating in post-WWII West Germany, the system aimed to combine local representation through single-member electoral districts, with proportional representation by party lists.
Today, more than 70 years after the system was first used in the 1949 elections to the Bundestag, the system remains more or less unchanged. It has also seen adoption by other countries over the decades, most notably including Bolivia, Lesotho, New Zealand, and Scotland.
In this post, we’ll examine aspects of how MMP systems function, examine a few variants and alternatives within the MMP family of electoral systems, discuss possible lessons to learn from the German experience, and conclude with advice for American advocates of MMP systems.
How does an MMP system work?All MMP systems use two types of representatives: local representatives, and party representatives. The former type are elected from a single-member district, while the latter are elected through nationwide votes cast for the party. A calculation is used to award seats to parties, to ensure that each party has its proper share of seats.
The original German type, still used for Bundestag elections in 2020, uses a two-vote ballot. Voters elect a candidate to represent their district with their first vote, while their second vote goes to their preferred party.
In the German MMP system, district winners are seated first, using the first-past-the-post rule. Then, party list seats are awarded to qualifying parties. A qualifying party is defined as having won at least three district seats, or won at least five percent of the party list vote.
An algorithm then sequentially awards party list seats to under-represented qualifying parties, until each party has achieved its proper share of seats. The results get more and more proportional as the algorithm proceeds through the remaining seats.
Are there any variants of MMP?Some variants of MMP use a one-vote ballot. For example, elections to the Baden-Württemberg state house in Germany, voting for a district candidate also counts as a vote for the candidate’s party. Party list seats are awarded to the party’s remaining district-level candidates which performed well, but finished as runners-up in their respective districts.
MMP implementations can also vary depending on how party list seats are awarded. In Scotland, for example, groups of neighboring electoral districts form an electoral region, and it’s from these regions that party list seats are awarded. In other countries, the entire country is used as a single party list region.
The proportion of party list seats relative to district seats can also be adjusted. Most commonly, half of the seats are elected from districts, while half are elected from party lists. In Lesotho, two-thirds of the seats are elected from districts, while one-third are elected from party lists.
In countries which use a two-vote ballot, the type of party list vote can vary. A country might choose to use an open list for its party list seats, while another might prefer closed lists. Still others might prefer a list with both a generic and a personal ballot option.
There might also be a variation on the method used to determine district winners. A ranked ballot (such as the instant-runoff ranked ballot) can be used for district level winners, though this option has not yet been used in a public election from what I can tell.
As you can see, there are almost limitless possibilities when designing an MMP system. Electoral system designers have a broad range of tools at their disposal to create the MMP system most appropriate for their needs, according to the wishes of their people. In a lot of ways, it is very much the Swiss Army knife of electoral systems.
What can we learn from other countries’ experiences with MMP?In a word: overhangs happen. These can occur with any MMP system which uses two-vote ballots. Put simply, an overhang is what occurs when a party wins so many district-level contests that it actually breaks the correction mechanism, and becomes disproportional. This can happen when one party ekes out many victories based off of pluralities on thin margins.
Historically, there has been a lot of litigation in German courts about how to properly handle overhangs, leading to a diversification of systems at the state level to address these problems. Usually, this has taken the form of leveling seats, extra party list seats added to the legislature to address the disproportionality. However, this may cause the legislature to swell beyond its normal size.
Tactical voting can also occur at the list level, in which some voters deliberately pick a party they don’t 100% support, in order to guarantee the presence of a coalition partner for their preferred party. This occurred in a German legislative election, where some deliberately vote for the FDP to get them across the 5% national threshold, so that the CDU would have another friendly party to form a cabinet with.
Decoy list attacks can also compromise the compensatory mechanism if it is not carefully set up. This occurs when a party deliberately splits itself into two wings, where one contests only the district seats, while the other contests only the party list seats. This occurred in Albania during the 2005 parliamentary elections, and was so egregious that Albania decided to scrap the system altogether.
That’s not to say that all MMP systems are necessarily prone to producing lots of overhangs or being vulnerable to decoy list attacks. It may be worth it for designers of MMP systems to investigate issues pertaining to the appropriate threshold level, whether a ranked ballot may be appropriate for their country, or whether it’s better to experiment with a one-vote format.
A dual threshold system may also be instituted, requiring parties to win both a minimum number of district seats AND a percentage of the list vote in order to be eligible for compensatory seats.
What should American MMP advocates conclude?MMP is a wonderful system that in many ways, can substantially boost the political diversity and level of representation of different parties in our state houses. However, like any other system, seemingly tiny details matter with how the system is configured. MMP is less a singular system and more a family of systems, and the plethora of options available in system design should be duly considered.
MMP is compatible with ranked choice voting if a two-vote ballot is used. It may even reduce the vulnerability of the system to producing disproportional results, since it requires a majority consensus on transfers, and is unlikely to produce close district elections with many wasted votes.
If a regionalized party list seat pool is desired, it’s generally wise to keep these regions organic and respectful of local communities of interest. They need not return an equal number of list seats, but the proportion of population to regional representative should remain the same across all districts.
To avoid producing many overhangs, it’s best practice to keep the number of district seats to no more than 60% of the total seats to be elected. Any further, and you are likely to produce results that more closely resemble FPTP results, than a proportional system.
This has been a very long post from me about MMP systems. I hope you enjoyed and would like to discuss in the comments.
