Today’s Nikkei print edition has a great Q&A about Japan’s proportional representation system. Here is my explanation for how it works, borrowing from that Q&A and some Internet sources:
- There are 180 seats (of the lower house’s 480) that are decided by PR. The country is divided into 11 regions, or “blocks”, which each receive some of the 180 seats. In addition to voting for a candidate in their single-member district, voters write in the name of the party they wish to receive their region’s PR seats. Votes remain valid if they are for an individual running on that party’s PR list, or if they are for the party leader.
- Seats are awarded using the D’Hondt method. Though somewhat complicated, this is a fair system for allotting the seats as intended. Putting it in my own words would be tough, so I’ll just quote Wikipedia:
In a closed list system, each voter casts a single vote for the party of their choice. In an open list system (such as Japan’s), the voter votes for a candidate personally, but the vote is principally counted as a vote for the candidate’s party.
After all the votes have been tallied, successive quotients or ‘averages’ are calculated for each list. The formula for the quotient is , where:
- V is the total number of votes that list received; and
- s is the number of seats that party has been allocated so far (initially 0 for all parties in a list only ballot…)
Whichever list has the highest quotient or average gets the next seat allocated, and their quotient is recalculated given their new seat total. The process is repeated until all seats have been allocated.
If you don’t want to go through the calculation, you can use the following shorthand for your region – for example, for a party to win one of Tokyo’s 17 PR seats, it needs to garner 1/17 of the vote, or 5.9%. Every 5.9% of the vote after that gets it another seat. It’s not precise but it’s a rough indicator.
- Parties are required to submit a list of PR candidates in advance, with candidates prioritized by region. For example, the LDP’s list prioritizes incumbents, many of whom are also running in single-member districts (see below).
- Candidates are allowed to run both in a single-member district and one PR block. This means if the candidate loses in the single-member district, he or she can still be sent to the Diet if the party wins in the PR block.
- It is possible to give two or more candidates the same level of priority if they are running in single-member districts (they then act like understudies for each other). A double-candidate who wins in the single-member district is automatically withdrawn from the PR list and the understudy takes his or her place. Note that in the LDP’s list, the first 22 candidates are all tied for first in priority. If only one wins in the PR block, then all 22 will get seats before the 23rd candidate.
- PR candidates who were given equivalent priority who lose in the single-member districts are not given sub-ranks ahead of time. The seats will be alotted among them in order of who came closest to winning in their respective single-member districts. So if Yukari Sato loses in Tokyo’s 5th district by just 1,000 votes and Yuriko Koike loses in Tokyo’s 10th by 2,000 votes, then Sato would be given priority over Koike.
- If a party wins in an unexpected landslide, there is a possibility they could fail to field enough PR candidates to satisfy the voters’ mandate. In that case, it sucks to be them because the seats go to the party who got the next greatest number of votes. This happened in 2005 when every candidate won on the LDP’s PR list in the South Kanto block, resulting in the election of 25-year-old Taizo Sugimura. They had enough votes to get at least one more seat but had to give it up to another party (story courtesy of Lord Curzon). This strikes me as a little undemocratic, since that means a party that the voters specifically voted against will win a seat.