關於選民投票率高低的制度成因，傳統觀點強調選舉制度會影響選民投票率。過去的研究普遍發現，以比例代表制為國會選制的國家，其國會選舉的投票率通常高於採行單一選區相對多數制的國家。也有研究發現，以兩輪決選制為總統選制的國家，其總統選舉的投票率通常高於採行相對多數制的國家。本研究則進一步指出，投票率不僅受到選舉制度影響，也可能受到憲政體制類型影響。本文假設，就國會選舉的投票率而言，在內閣制與偏內閣制的半總統制（總理總統制）國家，其投票率整體而言應會高於總統制與偏總統制的半總統制（總統議會制）國家。就總統選舉的投票率而言，在總統制與偏總統制的半總統制（總統議會制）國家，其投票率整體而言應會高於偏內閣制之半總統制（總理總統制）國家。本研究將觀察全世界民主國家的國會與總統選舉投票率，以驗證上述假設，並將分析世界各國在不同選舉制度與憲政體制的組合下選民投票率的差異，以檢證選舉制度與憲政體制這兩項制度因素對選民投票率的綜合影響力。
Regarding the institutional factors of the voter turnout, the traditional view emphasizes that the electoral system will affect voter turnout. Previous researchers have found that in the parliamentary elections, the voter turnout under the proportional representation system is higher than that under the plurality with single-member-district system. Past studies have also discovered that in the presidential elections, the voter turnout under the two-round system (majority system) is higher than that under the plurality system. This study further points out that the voter turnout is not only affected by the electoral system, but also by the types of constitutional system. The study makes the hypothesis that as for the voter turnout in the parliamentary elections, the voter turnout under parliamentarism and premier-presidentialism should be higher than that under presidentialism and president-parliamentarism. As for the voter turnout in the presidential elections, the voter turnout under presidentialism and president-parliamentarism should be higher than that under premier-presidentialism. This study will observe the voter turnout in democracies around the world to verify the above hypotheses. Besides, the study will also analyze the differences in voter turnout between countries under different combinations of constitutional systems and electoral systems, to confirm which of these two institutional factors (i.e. constitutional system and electoral system) has a greater impact on the voter turnout, and verify the combined influence of these two institutional factors on the voter turnout.
