2010年11月27日舉行的三合一選舉，是我國地方自治史上首次的「五都直轄市」選舉，選民同時擁有市長、市議員與里長選舉的三張選票。本文的目的，即是針對當選民擁有兩張以上之選票，且每項公職選舉又有兩位以上之候選人，指出幾種初探與分析選民「一致投票」(straight-ticket voting)與「分裂投票」(split-ticket voting)模式的方法，並以2010年的高雄市三合一選舉為例來說明。大體而言，由於選舉制度特性以及選舉層級差異，不同公職選舉的政黨競爭程度也有所差異。單一選區特性將導致兩強的競爭，複數選區SNTV制度則較有利於兩大黨以外的政黨獲取席次。在這次高雄市長選舉，脫黨參選之楊秋興取代國民黨黃昭順，成為在選舉中與民進黨陳菊競爭的主要候選人，其票源從分析中證實部分來自泛藍陣營認同的選民，換言之的確存在「棄黃保楊」的選民策略投票。在市長選舉採策略投票支持楊秋興的藍營選民，多半在市議員選舉中則回歸國民黨或投給親民黨候選人，形成一種分裂投票的形式。而綠營選民則在市長與市議員兩票呈現較高程度的一致投票。至於里長選舉，選民的里長黨派投票選擇，似乎與其市長與市議員兩票間並無顯著的關係，此亦凸顯里長選舉與其他兩者在競爭特性上的差異。

Three-in-one election held on November 27th 2010 is the first five metropolitan elections in the history of Taiwan’s local elections. Voters in this election could cast three ballots for different political positions: mayor, city councilor, and head of li. This study focuses on the Kaohsiung city and analyzes voters’ straight-and split-ticket voting in the 2010 three-in-one election. In general, the character of electoral competition is shaped by electoral systems and the level of election. Single-member district with plurality system is considered to contribute to a competition between two major parties, whereas minor parties are more likely to survive under the SNTV-MMD system. In the 2010 Kaohsiung mayoral election, then DPP incumbent Kaohsiung County Magistrate Chiu-hsing Yang ran for mayoral election as an independent candidate and replaced the KMT candidate, Chao-shun Huang, as the major competitor of incumbent mayor, Chu Chen. Our study finds that indeed some pan-blue partisans voted for Yang strategically in the mayoral election. This finding to an extent confirms the rumor of “dump Huang and save Yang” before the election. Meanwhile, most of those pan-blue partisans who voted Yang for mayor remained to support pan-blue candidates in the city councilor election, showing a split-ticket voting pattern. In contrast, pan-green partisans demonstrated a high degree of loyalty to the DPP mayoral candidate, Chu Chen, and the pan-green candidates in the city councilor elections. As for the lowest-level election of head of li, our study shows that there is no significant relationship between vote choice of head of li and that of mayor and city councilor. This finding indicates that the character of the election of head of li is quite different from that of mayor and councilor election.