The Sekihairitsu (惜敗率, literally the "narrow loss ratio", sometimes translated as "ratio of margin of defeat", "best loser calculation" or "second-chance rule") is a method used in the proportional representation (PR) constituencies ("blocks") for the Japanese House of Representatives to determine the order of candidates placed on the same list position by their party.
Under the PR system introduced in the 1996 general election for 180 (initially 200) of the House of Representatives' 480 (initially 500) seats, political parties are free to nominate candidates running or not running concurrently in one of the 300 single-member first-past-the-post electoral districts. The parties may rank the PR list candidates they nominate in a regional "block" in any order they decide. However, they are allowed to (but don't have to) place some or all of the PR candidates concurrently running in a single-member district on the same position on their PR list. In that case, the sekihairitsu is used to determine the order of candidates. It is calculated by dividing the number of votes a candidate received in his electoral district by the district winner's votes. After all district winners are struck from the list – they already have won a seat and thus cannot be elected by PR – all remaining candidates put on the same list rank are then arranged according to their sekihairitsu in descending order.
While the sekihairitsu system allows – depending on a party's nomination strategy and electoral success – more successful candidates (those "narrowly losing" their districts) prioritized election by PR, it does not change the fact that the Japanese voting system is a parallel, i.e. non-compensatory voting system: The number of PR seats for a party is independent from the results in the single-member districts and is exclusively determined by the number of PR votes the party receives. And unlike the Open list proportional voting system used since 2001 in elections for the House of Councillors of Japan where voters may choose to cast a preference vote for a single PR candidate, the sekihairitsu system doesn't allow the voters any direct influence on the PR candidates elected.
Example
The Liberal Democratic Party (LDP) list in the Tōhoku PR block in the 2009 general election of members of the House of Representatives consisted of 24 candidates who were also running for district seats and four candidates who were only running on the PR list. The LDP ranked the candidates as follows:
The election result in the 2009 Tōhoku proportional race gave the LDP 27.9% of the vote and four seats. Of the district races, LDP candidates only won five, all from the 23 put on the same proportional list position. The first two elected PR representatives were Masayoshi Yoshino (who lost to Kōichirō Gemba by 56,858 votes to 159,826) and Ken'ya Akiba. To determine the other two elected proportional representatives, the Sekihairitsu comes into play: