This study conceptualizes political polarization in contemporary democratic countries as "polarization of the party system." It hypothesizes a causal flow where voter preferences are mediated by political institutions to determine "polarization of the party system." The study examines the factors and mechanisms that determine the degree of polarization using various approaches. As a result, it was shown that the intensification of competition among opposition parties in electoral districts leads to increased polarization of policy preferences among candidates and voters. On the other hand, the mitigation of competition through the unification of candidates promotes the moderation of candidates' policy positions. Furthermore, at the voter level, while partisanship influences the choice of conversation partners, it was found that continuous observation of others' behaviors helps prevent polarization.

政治経済学・公共選択論の主な数理モデルは、米国の政治制度を強く意識したものが多い。しかし、二大政党制や大統領制など、米国の政治制度は欧州やアジアの民主主義国から見れば特殊なものである。政治制度の在り方が政策の意思決定過程に与える影響を考えるうえで、米国以外の政治制度を想定した研究が必須であると言える。そこで本研究では、日本や欧州などの議院内閣制を分析する理論的枠組みを構築していくことを目的とする。特に、議院内閣制の特徴の1つである内閣不信任決議、および首長が有している議会解散権に着目する

This project investigates the effect of a possible risk of cabinet termination on political agency problem (moral hazard and adverse selection). First, the possibility of cabinet termination can incentivize a prime minister or government to increase their efforts. Consequently, this may reduce the related moral hazard problems. Second, the possibility of cabinet termination can improve the quality of governance. This is because a prime minister or government exhibiting undesirable characteristics such as low competence to their voters should be dismissed through the cabinet termination. Thus, a more competent government is more likely to survive.

This study develops a formal model in which a candidate strategically decides both a campaign platform and a policy to be implemented while most of past studies consider only one of them. Especially, this study supposes that a candidate who implements a policy that differs from his/her platform must pay a cost of betrayal. The model is able to show two implications that previous frameworks have had difficulty with. First, candidates with different characteristics have different probabilities of winning an election. Second, candidates who prefer an extreme policy won some elections. Moreover, this study also shows some difficulties to explain why candidates announce ambiguous platforms

Politicians prefer to use vague words andoutline several policies in their electoral promises, which is termed as"political ambiguity." It is reasonable to interpret politicalambiguity as a lottery, that is, a probability distribution on policies, in thefollowing manner: Candidates announce a lottery, and a voter chooses acandidate who announces a better lottery for themselves. However, it is stilldifficult to explain why politicians prefer to use vague promises (i.e., alottery) based on a rational-choice model.To understand the difficulties in thisregard, we should begin by locating a Condorcet winner that allows politicalambiguity. Black (1948) shows that if we suppose that voters can choose only asingle policy, a unique Condorcet winner is at the median policy (i.e., themedian voter's preferred policy). On the other hand, my work supposes a lotteryinstead of a single policy, which is called a Condorcet winning lottery: Alottery that defeats or ties with all other lotteries in pairwise elections. Insummary, the unique Condorcet winning lottery is the median policy when votersare risk-averse or risk-neutral, while its existence is not ensured when votersare risk-loving.

This projectoffers a new explanation for the entry of third-party and independentcandidates into the US state-level elections. We argue that the economicbenefits of holding an office is what motivates amateur politicians to run,predicting that amateur politicians find holding an elected office particularlyattractive when the private sector is struggling. This is because, during therecession, amateur politicians view that an elected office is a more attractivesource of income as compared to private jobs, while pursuing political power tochange the economic prospect by adopting a new policy. Building on thisargument, we hypothesize that as the unemployment rate increases, the number ofthird-party and independent candidates increases. Our analysis with panel dataof state house, state senate, and gubernatorial elections in 48 US statesbetween 1980 and 2010 reveals that the hypothesized relationship existed onlyfor state legislative elections. To explain why these candidates run, despitetheir very small probability of winning, we extend the prospect theory tosuggest that these candidates may overestimate their probability of winning.