單一選區兩票制下的一致與分裂投票：2008年立法委員選舉的探討

Abstract

2008年立委選舉改採單一選區兩票制，讓台灣選民首度有機會針對同一職位投下兩張選票。本文利用民意調查資料與多層模型的建立，檢視選民採取一致與分裂投票的各種型態及其影響因素。研究結果發現，有高達76.5%的選民採取一致投票，其中47.6%一致投給國民黨，28.7%一致投給民進黨，台聯及客家黨的一致投票則僅合佔0.2%。而採取分裂投票的選民，不論「有無機會」採取一致投票，都出現以藍綠光譜爲主的「聯盟投票」型態。此外，策略投票不但發生在小黨認同者的第一票身上，在政黨票上也會有策略投票的考量，甚至部分國民黨或民進黨認同者，在聯盟席次最大化的考量下，也會將政黨票轉投給同聯盟小黨。多層模型的結果則顯示，年紀愈輕、政治知識愈高，以及對選區候選人的偏好與自身黨性相衝突的選民，皆有顯著偏高的相對機率採取分裂投票。黨性愈強，採取分裂投票之相對機率也愈低。至於當選區中有脫黨參選或強勢獨立候選人參選時，選民即有顯著偏高的相對機率採取分裂投票，凸顯出個人選票在單一選區中的影響效果。而在農業人口比例愈高、政黨版圖勢力愈不明顯的選區，選民採取分裂投票的相對機率也愈高。

The 2005 constitutional amendment in Taiwan adopts a new mixed-member majoritarian (MMM) electoral system to replace the single nontransferable vote (SNTV) system for legislative elections. The election of the 7th Legislative Yuan held on January 12 of 2008 marked the beginning of a new era of Taiwan`s legislative politics since it was the first ever election in Taiwan under the MMM system. Each voter cast two votes: one for the single-member district (SMD) candidate, and the other for the party list. It is interesting to ask how voters allocate their two ballots. This paper analyzes patterns and determinants of straight-and split-ticketing in Taiwan`s 2008 election with a multilevel model which integrates individual-level survey data and district-level macro variables. We find that straight-ticket voting is dominant (76.5%), with the KMT claimed 47.6%, the DPP obtained 28.7%, and other small parties, only 0.2%. As to split-ticket voting, the pattern tends to follow the party coalitions of the blue versus green camp. Furthermore, we find that not only small party identifiers tend to vote strategically for the major party candidates of their own \"color\" camp, as Duverger`s law predicts, but some major party identifiers also vote tactically for small parties of their camp on the PR ballot in order to maximize the total number of seats of their preferred coalition. Our multilevel model reveals that, at the individual level, voters who are younger, with higher political knowledge, weaker partisanship, and do not like their parties` nominees are more likely to split their tickets. At the district level, on the other hand, voters who reside in districts with candidates broken off parties or with strong independent candidates are more likely to cast split tickets. This is an indication that personal voting still plays a role in SMD ballots.