Team Mirai has proposed a new seat-allocation method called the "Sunlag method" to change how proportional representation works in Japan [1, 2].
The proposal seeks to make the legislative process more reflective of the public will by lowering the barriers for small- and medium-sized parties to secure seats [2].
Suzuki Keisuke (LDP), chair of the House of Representatives election-system council, presented the proposal during a council meeting on Tuesday, Aug. 25 [1, 3]. Suzuki said it may be necessary to consider a proportional system that allows for a better reflection of the public's will [1].
Under the current D'Hondt method, seats are allocated using a divisor sequence of one, two, three, and so on [1]. This natural number sequence often favors larger parties, as they can secure multiple seats before smaller parties reach the threshold for their first [1].
The proposed Sunlag method, or modified Sunlag method, would replace natural numbers with a sequence of odd numbers: one, three, five, and so on [1]. By increasing the divisor for subsequent seats, the system makes it more difficult for large parties to obtain a second or third seat [2].
This mathematical shift is designed to distribute seats more broadly across the political spectrum. According to a statement from Team Mirai, using the Sunlag method ensures that seats are more easily rotated to small- and medium-sized parties [2].
While some reports indicated the proposal surfaced as early as Aug. 10 [2], the formal council discussion took place this week [1, 3]. The council continues to evaluate whether this modification provides the optimal solution for the current election system [1].
“The proposal seeks to make the legislative process more reflective of the public will.”
A shift from the D'Hondt method to the Sunlag method would represent a fundamental change in Japan's democratic architecture. By penalizing the 'efficiency' of large parties in gathering multiple seats, the system would likely lead to a more fragmented parliament with a higher number of minority parties. This could increase political diversity but may also make it more difficult for any single party to form a stable majority government.
