「92共識」對2012年台灣總統大選的議題效果：「傾向分數配對法」的應用與實證估算

The Issue Effect of the '92 Consensus' on 2012 Taiwan Presidential Election: An Application and Empirical Assessment of Propensity Score Matching

2012年總統大選後，許多輿論均評論此次的大選結果與「92共識」此一有關兩岸關係的議題，有莫大關係。本文旨在探究92共識對2012選民投票抉擇的影響程度。本文重新疏理了「議題投票」理論的核心定義、適用範圍與分析方法，以92共識的議題效果為研究焦點，依其議題性質假定了「議題內生於政黨認同」的關係，且準於「由因視果」的分析途徑，根據「2012台灣選舉與民主化調查」的電訪(TEDS2012-T)與面訪(TEDS2012)資料，運用「傾向分數配對法」，來估算92共識對台灣選民投票抉擇的影響。本文研究發現：在競選期間，92共識對馬吳配的支持度約有2成的影響，對蔡蘇配約有1.3成；至選後，92共識對馬吳配的議題效果大幅降至約1成的影響，對蔡蘇配則略降為1.2成。這項控制「內在選因」後的實證發現，有效且精確地估算出2012競選期間，92共識對選民投票行為的議題影響效果。此外，透過不同時間點的估算，資料亦證明了，92共識的確在競選期間成功地被轉化為藍綠選民所注意的顯著性議題，對選舉結果具有一定程度的影響。

News and many public comments indicate that the '92 consensus' was the crucial issue to affect the result of Taiwan 2012 presidential election. This paper aims to study the effect of the 92 consensus on voters' choices in 2012. This paper reviews the core assumptions, boundary of application and analytical methods of the 'issue voting' theory. Moreover, it focus on studying the impacts of the 92 consensus that are presumed to be endogenously correlated with party identification. Based on the approach of 'studying the effects of a cause', as well as using the '2012 Taiwan's Election and Democratization Study' dataset (TEDS2012-T and TEDS2012), this paper applies 'propensity score matching' (PSM) method to investigate the issue effect of the '92 consensus' on voting choices during 2012 election. The results from the data analysis demonstrate that positions supportive of the '92 consensus' account for about twenty percent of supporting rates to pro-Ma voters in the period of the electoral campaign; meanwhile, positions oppositional to the '92 consensus' would contribute about thirteen percent of supporting rates for pro-Tsai voters. After the election the influential probability of the '92 consensus' was dramatically downsized to ten percent of supporting rates to pro-Ma voters; however, the percentage for pro-Tsai voters was slightly reduced to twelve percent. These findings provide more valid and credible estimates toward the influential probability of the '92 consensus' issue during the 2012 elections. Moreover, the statistical findings over various time-points also verify the successful transformation of the '92 consensus' to be identified as a salient issue across pro-Ma and pro-Tsai voters. It indeed achieved substantial influences toward the processes and result of 2012 presidential election.