衆議院の選挙制度が中選挙区制から小選挙区比例代表並立制に変更されてから、1996年以降、幾度となく並立制下で衆議院議員選挙が実施された。その間、「以前に比べて、改善されていない」と言う並立制に対する批判と「まだ回数を経ていないのでわからない」と言う擁護論が共存している状態であった。しかし、並立制導入から20年を経たことにより、一定の結論を出す時期に来たと考える。そこで、本研究では、政治改革以降の日本政治の変容という視点から代議制民主主義の変容と課題について検討することにした。つまり、政治改革の導入の際に意図した通りに日本の代議制民主主義が機能しているのかどうかを実証的に明らかにするとともに、何が課題として残されているのかについて提示することにした。なお、代議制民主主義の変容を分析するに際して、代議制民主主義の質を測定しなければならない。従来の研究では、与党と野党の得票率や議席率の比などの外形的な指標に基づいて測定していたが、与党の得票率や議席率が高くても、有権者が望む政治を行った結果なのか、異議申し立てが事実上、閉ざされている結果なのかを区別することができない。そこで、本研究では、従来の外形的な代議制民主主義指標に替わり、代議制民主主義の機能という点から新しい指標を構築し、その指標に基づいて日本の代議制民主主義を測定することにした。具体的には、「政治家が提示した公約の中で、有権者が自分の最適点に最も近いものを選び、投票行動を決定する」ことを通して「自分達のことを自分達で決定する」という代議制民主主義の擬制が成立しているかどうかを検証することにした。
It is often assumed that unlike the "hard" sciences, experiments cannot be conducted in the humanities or the social sciences. That said, when a major systemic change occurs in a social or political context, it is possible to carry out a "social experiment" by comparing the situation before and after this change. In this research, I performed such a social experiment by testing whether changes made during a period of political reform in the 1990s to the electoral system for the House of representatives (or "Lower House") of the Diet (Japan's bicameral national parliament) produced the intended effects. There are two basic types of democratic systems: an Anglo-Saxon system in which candidates are elected in single-member districts (SMDs), with the preferences of the minority of voters not reflected in the outcome, and a consensus-type system using proportional representation (PR) to elect candidates according to the percentage of the total vote their parties secure, thereby better incorporating the preferences of all voters. The system of voting in multi-member districts used for Lower House elections prior to electoral reform in the 1990s can be regarded as a quasi-consensus model of democracy with some PR elements. In contrast, the post-reform system, which primarily uses SMDs but also elects candidates in regional PR "blocks," can be viewed as an Anglo-Saxon-type model of democracy. Though a majority of seats in this "parallel" system are won through SMDs, there are a number of candidates who lose in SMDs but are subsequently elected in PR blocks because "dual candidacy" allows them to be included on party lists in those blocks. However, candidates who lose in SMDs but secure Diet seats in PR blocks work toward winning in SMDs instead in the next round of Lower House elections, ensuring that despite this being a "parallel" electoral system, the importance within it of SMDs relative to PR blocks is considerable. Elections for the Lower House have been held on several occasions since 1996 using this post-reform parallel system. During this period, critics of the new system have alleged that it has not produced improvements, while supporters have argued that there have not yet been enough elections to be able to evaluate its effects. My view is that with 20 years having elapsed since the parallel system's introduction, the time has come to draw a number of conclusions about its impact. With this goal in mind, this research considers changes in representative democracy and related issues from the perspective of changes in Japanese politics following political reform. Stated differently, I empirically test whether representative democracy in Japan is functioning as was intended when political reform was carried out as well as seek to identify other issues left to address. To analyze changes in representative democracy, its quality must be measured. In previous researches, such measurements were made based on external indicators such as the proportion of votes or seats won by the ruling party or parties versus opposition parties. However, even if the proportion of votes or seats won by a ruling party is large, it is impossible to discern whether this was the result of widespread voter satisfaction with how it has conducted politics or because objections to the status quo are essentially being nullified. In this research, I set aside these conventional indicators and instead create new measures that focus on the functional aspects of representative democracy to evaluate representative democracy in Japan. Specifically, I test whether a false narrative has developed for representative democracy whereby it is believed that this system gives individuals the power to make critical decisions shaping their lives in line with their preferences by voting for politicians whose campaign pledges they think are most closely aligned with those preferences.