選制轉變過程下杜佛傑心理效應之檢視：從日本眾議院選制變革的經驗來觀察

Abstract

選舉制度的設計，不僅攸關各國政黨體制的運作與國家政府體制的鞏固，甚至對政府執政領導人事的更迭、政策制定的變遷，均有深刻的影響。對選民投票行為來說，更會因不同選制結構而展現出不同的決策思維。因此選制的相關規範設計，無疑是形塑先進民主國家政治體制運作的基礎，而選制變革過程中所產生的政治效應，更值得學界深入進行評估與檢驗。 \r\n本文根據日本選舉研究(JES)所彙整的定群追蹤調查，針對九零年代日本新舊選制的轉換過程，探析選民對政黨支持偏好的動態過程，是否依循杜佛傑法則(Duverger`s Law)的立論。研究結果顯示，日本眾院區域席次的競爭，在改採單一選區後確實對具競爭實力的主要大黨較為有利。透過統計模型的分析，本文更進一步發現除了選民政黨認同會影響選票基礎外，區域席次改採單一選區多數決後，制度的結構誘因確實發揮了預期效果。原本在單記非讓渡選制中支持弱勢小黨的選民，在選制變革後將會考量候選人的勝選機會，策略性地將選票集中支持較有當選希望的候選人，並通常是以大黨所推出的競爭者較佔優勢。這樣的結果，也驗證了杜佛傑法則所推論選舉制度影響選民投票抉擇的方式。

Electoral system is imperative to define the party system in a country. It also helps to consolidate the political regime, to formulate public policies, and to alternate government leaders in the office. From the constituent`s point of view, different electoral rules influence the behaviors and the way of voting as well. It is therefore without question that the electoral system is essential to regulate political systems in any democracy. \r\nThis paper, based on the panel data collected from the Japanese Election Study (JES), tries to understand the political impacts of the electoral reform in Japan in the 1990s. Specifically, in accordance with the Duverger`s Law, we try to detect the dynamic voting transition under the evolution of new electoral system in Japan. The statistical result shows that, after adopting the Mixed-Member Majoritarian System in the district Representatives, the dominant parties took the advantage by attracting more votes than before. In addition to the party identification, we find that the new electoral rule itself contributes to the dominant parties as anticipated. That is, those who support the uncompetitive parties in 1993 when the Single Nontransferable Vote was used, were likely to conduct the strategic voting by switching their votes to the dominant parties in 1996. In general, we find the empirical support for the Duverger`s Law in the transition of electoral reform in Japan.