選制改革對立委競選策略之影響： 大型語言模型之應用

Abstract

在政治學中，選舉制度的變革一直是相當重要的研究問題。關於立法委員的立法行為或是選民投票行為等議題，過往文獻可說汗牛充棟，然而對於選舉制度變革對選舉前競選行為之影響的討論卻並不多見。有研究者發現，當選舉制度由複數選區單記不可讓渡制轉變為單一選區相對多數決制下，日本議員候選人的競選策略會轉為更加關注全國性政策，並提出更多的政策綱領型政見。然而本研究發現，在臺灣的案例中，選民對自己選區的立委有更高的辨識度，候選人更容易居功於有利選民的政見，區域立委會傾向提出更多有利於選區利益的政見，意即肉桶立法會在選制改革後更加明顯。具體來說這是因為，選制改變後，選區規模縮小與選民課責性增加，候選人的競選邏輯因此改弦易轍。進一步以臺日比較的視野觀之，肇因於非內閣制與內閣制的不同以及重複提名制度的存在與否等制度上的差異也導致了日本的候選人有額外動機來提出政策綱領型政見，臺灣的候選人則付之闕如。 為了對此假設進行驗證，本研究使用中央選舉委員會之選舉公報，整理第二屆至第十一屆中華民國立法委員選舉的資料，以Latent Dirichlet Allocation和BERTopic主題模型建模分析選舉公報和政見之間的相似性。此外，本研究運用深度學習、人工智慧與提示工程之利，透過Least-to-Most與Chain-of-Thought的提示技術，自動化生成分類的評斷結果，降低過往對於人工判斷的主觀性問題。 本研究發現：國民黨以及民進黨候選人在2005年的選舉制度改革之後，由於選區規模縮小和同質性提高，新選制下選民的可課責性增加，也沒有同黨候選人的競爭壓力，立委更容易被選民所辨識出來，會提高候選人對於肉桶立法的關注程度，因此在單一選區下更有強烈動機提出有利於選區的政策並經營個人選票；相反的，小黨候選人則不太受到選制改變的影響，因為這些候選人並未在競爭環境上有太大的改變，他們仍然面臨到國民黨和民進黨對手的壓力，這些變化都在統計上具有顯著的結果。綜合來說，本研究驗證了選舉制度對於臺灣立委候選人競選策略的影響，並揭示選舉制度並非單一的影響因素，儘管如此，礙於資料取得的限制，本研究未能推論其他因素如憲政體制、重複提名制或是選民期待對候選人競選策略的因果機制。此外，本研究建置一個涵蓋第二屆至第十一屆選舉公報的資料庫，為未來的研究提供了相關資源。

Electoral system reform has been a significant research topic in political science. While extensive literature exists on legislators' behavior and voter conduct, fewer studies address how changes in the electoral system impact pre-election campaign strategies. Research shows that when Japan shifted from the single non-transferable vote (SNTV) system to the single-member district (SMD) system, candidates focused more on national policies and proposed more policy-oriented platforms. However, in Taiwan, voters have higher recognition of their district legislators, and candidates tend to propose more district-specific policies after the reform. This phenomenon, known as pork-barrel legislation, became more prominent due to reduced district size and increased accountability. The differences between Taiwan and Japan are further influenced by their respective constitutional political systems and the presence or absence of dual candidacy practices. To test this hypothesis, this study analyzed election manifestos from the 2nd to 11th Legislative Yuan elections using Latent Dirichlet Allocation (LDA) and BERTopic models. Additionally, we utilized deep learning, artificial intelligence, and prompt engineering techniques such as Least-to-Most and Chain-of-Thought to automate classification and reduce the subjectivity of manual coding. The findings reveal that after the 2005 electoral reform, candidates from the Kuomintang (KMT) and Democratic Progressive Party (DPP) increased their focus on pork-barrel legislation due to enhanced voter accountability and reduced intra-party competition. Conversely, minor party candidates were less affected by the reform, continuing to face significant competition from major parties. These changes were statistically significant. This study validates the impact of electoral system reform on Taiwanese legislative candidates' campaign strategies and highlights that electoral systems are not the sole influencing factor. Due to data limitations, we could not infer causal mechanisms related to constitutional systems, dual candidacy practices, or voter expectations. Additionally, we created a comprehensive database of election manifestos from the 2nd to 11th elections, providing a valuable resource for future research.