On Germany's election system
The German Federal elections must meet the requirements of Article 38, §1 of the German constitution, “the delegates of the German Parliament (Bundestag) […] are elected in a general, direct, free, equal and secret vote.” This article talks about how Germany does proportionality, overhang seats, inverse success values and their threshold rules. It also looks at how problems represent themselves in the UK. …
The requirement for an equal vote is the reason they use a form of proportional representation. It is a form, possibly the definitive version of the Additional Member System.
The German Bundestag has 709 members at the moment. It elects 300 from constituencies, which would make them over 2½ times those in the UK, but they supplement them with at least 300 from regional lists, however the number elected from the list is defined by meeting the proportionality rules, there is not an absolute number. The allocation of list seats to regions is done from the national level.
It is possible that a party does so well in the constituencies within a region that it needs less seats than the amount won to meet its share; in this case, the other parties are allocated more seats from the list, and these allocations are across all regions. This is called an overhang. An overhang mandate does not have to be given to a majority party in a region.
Historically there was an effect called inverse success value, where additional party i.e. list votes in a region where the Party had an overhang mandate might lead to that party losing seats in another region. This has been supposedly rectified by law, although opinion be divided.
In order to win representation in the Bundestag, a Party must win either three seats in the constituencies within a Region or 5% of the national vote.
The Party’s regional lists must be ordered by a secret vote. Wikipedia says, “The applicants from a party must be elected in a democratic and secret election by an assembly of the party members in a constituency” This reads as a translation, I am looking to see what this means, but it does mean that a Labour Regional conference could not perform this role.
One reason to study these things is that we can learn from it and, depending on your hobbies, the mathematics are interesting. Nearly every system has a counter system that gains it.
Germany solves the Alba problem with its 5% threshold. A list only party, not represented in Parliament would need 2000 nominators to support them and then need 5% of the national vote since it could not win three seats. In Germany, recognised minority parties do not need to meet the threshold.
In the UK, the SNP achieve an overhang mandate, as do the Tories in England. In London, in 2016, the surprise victory in Merton and Wandsworth constituency mean that Labour’s list seat representation went down from four to three, although the number of Labour AMs remained the same.