Youth Turnout in Referendums and Elections: Evidence from Regression Discontinuity Designs

Abstract

This study addresses an interesting question on political participation in direct versus representative democracies. That is, are citizens more likely to turn out to vote in direct issue-oriented referendums or in indirect candidate-oriented public office elections? In order to answer this question, this study takes advantage of a rare case of a natural experiment in Taiwan`s 2018 concurrent referendum and local elections. Capitalizing on a gap between the voting-age eligibility rule of 18 for referendums and 20 for local offices, this study develops rigorous regression-discontinuity (RD) designs in causal inference with the ＂two cutoffs model＂ for the referendums and ＂the standard single cutoff model＂ for the local elections. The two RD designs are then applied to a unique set of individual-level validated turnout data with large sample size released by the Central Election Commission. Empirical estimates of the two RD designs confirm our hypothesis that, other things being equal, the first-time voters are much more likely to turn out when they are eligible for both referendum and public office ballots than when they are only eligible for referendum ballots. This finding has important implications not only for theories of direct versus indirect democracies but also in practice for democratic decision-making mechanisms.

創制與複決公投是針對議題表達贊成與否，屬於直接民主的參與管道；而公職選舉則是票選各級行政首長及代議士，屬於典型的代議民主。兩者雖都由公民進行投票，但各有其功能與特性。有趣的是：民眾比較會參與何者的投票？這個看似單純，只需比較歷屆公投與選舉投票率即可輕易回答的問題，卻暗藏了許多推論上的陷阱，以致實證結果頗多爭議。為了更嚴謹的回答此一問題，本文將我國2018年公投暨地方選舉中法定投票年齡之差異，視為可貴的自然實驗，以「斷點迴歸設計」分析選票型態對投票參與的效應。因2017年底修訂之公投法將公投年齡降為18歲，但公職投票年齡則維持20歲，此一法定年齡差異，彷彿將2018年11月24日前尚無投票經驗的「首投族」以20歲為界一切為二：18歲以上但未滿20歲者為「唯公投首投族」、滿20歲者為「公投暨公職首投族」。緊鄰20歲切點兩側的年輕選民，在各項特徵上都頗為相近，惟因公投法及憲法的規定卻享有不同的投票權，如果這兩類首投族在其均可投的公投案上顯示出不同的投票率，其成因便可歸之於兩者的最大差異：需年滿20歲才能享有的公職投票權產生之「催票效應」。倘若公職投票確實是參與投票的主力推手，那麼「公投暨公職首投族」與「公投首投暨公職二投族」（亦即2016年1月16日總統立委選舉時剛滿20歲者）的切點（22.856歲）兩側，投票率間應無顯著的差異。本文將「斷點迴歸雙切點設計」應用於2018年的公投案、「斷點迴歸單切點設計」應用於2018年的地方公職選舉，以中選會之領票記錄抽樣資料分析，實證結果均與上述假設相符，亦即公職選舉較具吸引力：「公投暨公職首投族」的公投投票率比「唯公投首投族」高出將近兩成；但公職之首投族與二投族間則無顯著差異。此一發現對直接民主及代議民主的理論與實務，均有重要之意涵。