Hirofumi Miwa

Does permitting voters to select multiple candidates in majoritarian elections increase diversity among those elected? While majoritarian systems typically use single-vote ballots, research suggests that allowing for multiple selections may increase the representation of women and racial minorities. However, empirical evidence regarding actual voter behavior remains limited. To address this gap, we conducted a survey experiment that varied the number of selectable candidates from one to three in multi-member local elections. The results revealed that, under the multiple-vote condition, respondents were more likely to alternate by gender, particularly in their second- and third-ranked choices, supporting the theory that multiple voting fosters more diverse representation. Nevertheless, men often emerged as the first-ranked choice, giving them an overall advantage at the aggregate level.

Understanding the ideological positions of political parties is crucial for empirically testing various theories in political science. In Japan, some studies have assessed each party’s policy outlook through electoral platforms, candidate surveys, or expert surveys, with most studies focusing on the past thirty years. However, limited efforts have comprehensively and longitudinally quantified the conflicts between political parties. Although previous studies have used election-related data to reveal interparty conflicts during elections, interparty conflicts between elections remain unclear. This study determines the stance of Japanese political parties during parliamentary debates. We collected text data from committee speeches from the Diet Proceedings Database from 1959 to 2019 and conducted a quantitative text analysis. By applying the Wordshoal method, we first estimated political party positions on specific policy topics in the House of Representatives and the House of Councillors. Then, we aggregated these policy-specific positions yearly via dynamic factor analysis. Consequently, we succeeded in discerning the axis of conflict in Japanese parliamentary debates and evaluated the longitudinal one-dimensional ideal points for political parties. Additionally, we visualized the changes in each party’s ideological position, identified controversial topics, and explored how these topics changed over time, providing new insights into the study of Japanese politics.

Voter preferences for a politician’s gender have been considered a potential factor of women’s underrepresentation in politics. Although recent studies demonstrate that voters do not generally dislike women candidates in elections, they may still doubt women’s competence and view persuasive behavior as counter-stereotypical for women. This may lead to the prediction that female politicians are less effective in persuading voters through their policy statements compared to men. However, evidence on this issue is scarce and mixed, with existing studies often having notable weaknesses in their experimental design. To address these problems, we carefully designed and conducted two preregistered survey experiments in the U.S. and Japan, where electoral rules are candidate-centered, and women’s underrepresentation is severe compared to other developed countries. We asked respondents how much they agreed with the policy statement of a fictitious politician whose gender was randomized in a mocked campaign website or a municipal council newsletter. We also varied the statement’s issue area and ideological position to examine whether persuasion is more effective when it aligns with gender stereotypes. The results showed no significant difference in policy persuasiveness between women and men politicians, and post hoc equivalence tests suggest the nonexistence of even minimal effects in both countries. Moreover, we found partial evidence that women politicians had an advantage when they claimed gender-stereotype statements in Japan, while the opposite was true in the U.S.

Detecting and addressing discrimination is one of the most crucial ways for ethnic and sexual minorities and women to fully integrate into the society. However, humans often fail to correctly judge what constitutes discrimination. The recent rapid development of artificial intelligence (AI) based on large language models (LLMs) has shown promise in assisting with this task, although its performance is understudied. This study investigates how humans and LLM-based AI, such as OpenAI’s ChatGPT, detect the concept of ‘discrimination’ and how their representation differs. Specifically, surveys were conducted asking humans (Japanese respondents) and ChatGPT (GPT-4) to evaluate the degree of discrimination in hypothetical unequal treatment scenarios presented to them. The scenarios varied in terms of targets, including their ethnicity, gender, and sexuality, and types of discrimination, such as those based on tastes, stereotypes, and statistics. The results show that ChatGPT generally classifies the scenarios as more discriminatory than humans do. However, ChatGPT also shares a tendency with humans to be more tolerant of unequal treatment based on ethnicity and gender compared to sexuality, and it is less likely to detect statistical discrimination than taste- or stereotype-based discrimination. Although LLM-based AI presents a potential tool for addressing discrimination and can offer temporary solutions, it may not fully capture all types of discrimination.

In coalition governments, while parties need to compromise with their partners to govern together, they also need to differentiate from the partners to please their supporters. How do coalition parties reconcile compromises with differentiation? We argue that coalition parties, especially junior partners, adjust their strategies to compromise or differentiate themselves from their partners depending on the level of public support for their partners. Parties tend to differentiate from partners when partners receive lower public support, and compromise with partners when they enjoy higher public support. To test this argument, we analyzed parliamentary speeches by legislators from a junior coalition partner in Japan. We applied a dynamic linear model to the results of machine learning text classification of legislators’ speeches. Our results show that as the senior party’s public support rate falls, the speech styles of legislators from the junior partner increasingly diverge from those of the senior partner’s legislators.

Incumbents often serve as critical gatekeepers in the recruitment of new candidates and may even designate their successors upon retirement. Some existing research indicates that the gender of gatekeepers is likely to affect the recruitment of female candidates, a dynamic of particular concern in countries like Japan, where political offices are predominantly held by men. However, it remains unclear whether the underrepresentation of women stems from male incumbents actively discriminating against female candidates during the recruitment process. Through a survey experiment involving over 7000 elected local politicians in Japan, we examine gender biases in the successor selection process and attitudes toward female candidacy. Contrary to our expectations, the results reveal that local politicians, irrespective of their own gender, are more inclined to nominate women over men as their successors. They also believe that these female candidates would receive support from their local constituencies. These findings suggest that the selection practices of incumbents may not significantly contribute to the underrepresentation of women in politics.

In Japan, the gender gap in attendance at 4-year universities is narrowing, yet significantly fewer women apply to selective colleges. A growing body of literature suggests that gendered expectations of educational returns and cultural stereotypes, most compellingly reflected in parental influence, are pivotal in shaping children’s college choices. However, the capacity to make causal claims remains limited in existing research, as observed gendered preferences among parents may merely echo earlier educational investments made before college applications. This study advances the field by leveraging a survey experiment approach. Our conjoint experiment, where respondents evaluate hypothetical college choices of fictitious children, yields several key findings. First, responses show no difference when the children, regardless of their gender, opt for selective colleges. Second, the respondents who expect higher returns from college education for men than for women tend to favor their fictitious son’s selective college applications. Third, fictitious daughters’ college choices are rated more favorably when they conform to societal gender stereotypes. These findings underscore the potential influence of recent admissions reforms in Japanese universities, including explicit quotas for female applicants, aimed at increasing their enrollment.

In bicameral legislatures, gender representation varies significantly between chambers. Historically, Japan's upper house has maintained a proportion of women twice that of the lower house. However, electoral systems alone cannot fully explain this disparity. We argue that seemingly gender‐neutral legislative institutions influence both voting behavior and candidates' willingness to run, contributing to significant disparities in gender representation in bicameral legislatures. To test this argument, we conduct two survey experiments exploring the underlying mechanisms from the perspectives of voters and candidates. Our findings suggest that informing voters about the upper house's subordinate role increases support for female candidates in upper house elections. Furthermore, women display a greater willingness to pursue office when assured of job security in the upper house, while men exhibit less interest when made aware of its limited authority to appoint the prime minister. This study enhances our current understanding of the effects of asymmetrical institutions between chambers from a gender perspective.

Japan is an intriguing case in the literature of judicial independence because of the Liberal Democratic Party's (LDP) long-lasting one-party dominance in government—which, in theory, leads to low independence. Although scholars have found plentiful anecdotal observations implying the LDP's judicial control, quantitative evidence remains scarce. Focusing on the Supreme Court as the first step, this study provides a new dataset on justices' ideal points through an extensive compilation of justices' voting data and application of the dynamic item response theory model. I validate the estimates' interpretability as ideological positions. The results present several novel findings: justices with a career-judge background are relatively conservative; the Chief Justice tends to be particularly conservative; the conservative camp has tended to hold on to a court majority since the 1960s; and the government's partisanship, to some degree, influences appointed justices' positions. These results reinforce scholars' views that Japan's court leans conservatively and aligns with the LDP, with implications for judicial independence in Japan.

Recent studies in democratic countries suggest that voters generally prefer candidates with specific personal attributes, such as being female and young. However, some of these patterns cannot necessarily be explained by voters’ expectations of candidates’ competence. Building on a growing body of literature that addresses populist attitudes as an important factor influencing voters’ political preferences, this study hypothesizes that candidates’ personal attributes shape voters’ perceptions of their populist attitudes and that such perceptions mediate the relationship between personal attributes and voter preferences. A conjoint experiment conducted in Japan showed that several personal attributes substantially influenced candidates’ perceived anti-elitism and people-centrism. An additional experiment to disentangle causal mechanisms suggested that, albeit inconclusive, young candidates were more likely to be preferred because of voters’ expectations of their populist tendencies. Methodologically, this study illustrates advancements in the conjoint experiment design to elucidate causal mechanisms, with a careful discussion of necessary assumptions.

We add new insights to the party theory of parliamentary debate proposed in Proksch and Slapin’s The Politics of Parliamentary Debate by combining a quantitative replication analysis of floor speeches with a qualitative explanation of the endogenous transformation of two institutions mediating elections and parliamentary speech in the Japanese Diet. Although the House of Representatives in Japan used a single non-transferable vote system with particularly strong personal vote-seeking incentives, our analysis based on a new dataset shows that, contrary to the theory’s predictions, the pattern of speech activities among party leaders and backbenchers is close to that of Germany, which has a party-centered proportional representation system. Such seemingly contradictory results, however, can be consistently understood within the scope of the theory if we consider the patterns of endogenous change in the parliamentary system and party organization. These results highlight the potential for further development of the theory.

This study examines the effect of perceived military threat on Japanese people’s opinion about Japan’s accession to the Treaty on the Prohibition of Nuclear Weapons. While nuclear aversion has been historically strong and deep-rooted in Japan, we expected that people would hesitate to support the treaty when reminded of the deteriorating security environment, considering recent experimental evidence suggesting that nuclear aversion is conditional and tends to fluctuate often and that Japanese citizens tend to be apathetic towards international laws. Moreover, we examine the possibility that pressure from foreign countries and international organizations reinforces people’s support for the treaty. Our survey experiment reveals that Japanese people are less likely to support Japan’s accedence to the treaty when they are primed with security threats, although the difference is small, and that this negative effect is limited to centrist and conservative citizens. However, we find no evidence that international pressure has the power to promote people’s support for the treaty.

The incumbent-led subversion of democracy represents the most prevalent form of democratic backsliding in recent decades. A central puzzle in this mode of backsliding is why these incumbents enjoy popular support despite their actions against democracy. We address this puzzle using the case of Philippine President Rodrigo Duterte. Although some Philippine analysts have speculated that his popularity was inflated due to social desirability bias (SDB) among survey respondents, there has been limited empirical examination. Our pre-registered list experiment surveys conducted in February/March 2021 detected SBD-induced overreporting at about 39 percentage points in face-to-face surveys and 28 percentage points in online surveys. We also found that the poor Mindanaoans, and those who believed their neighbors supported Duterte, were more likely to respond according to SDB. These possibly counter-intuitive results should be interpreted with caution because the survey was conducted during the height of the COVID-19 lockdown, and the findings cannot necessarily be extrapolated to the other period of his presidency. Nevertheless, this study suggests that preference falsification could be an alternative explanation for the puzzle of popular incumbents in democratic backsliding.

Growing evidence reveals that candidate issue engagement differs between men and women. However, recent research suggests that individual-level differences among candidates should be small under the strategic incentives inherent in single-member district elections that encourage party rather than personal-vote seeking. We examine whether men and women candidates emphasize different issues in their electoral campaigns and if the magnitude of the gender gap varies under different electoral rules. Our analysis of 7497 Japanese election manifestos spanning more than 20 years, from 1986 to 2009, reveals significant gender differences in the issues candidates emphasize in their electoral campaigns, regardless of party affiliation or other attributes. Moreover, these differences remain salient after an extensive change from a multi-member district to single-member district electoral system.

Understanding voters’ conception of ideological labels is critical for political behavioral research. Conventional research designs have several limitations, such as endogeneity, insufficient responses to open-ended questions, and inseparability of composite treatment effects. To address these challenges, we propose a conjoint experiment to study the meanings ascribed to ideological labels in terms of policy positions. We also suggest using a mixture model approach to explore heterogeneity in voters’ understandings of ideological labels, as well as the average interpretation of labels. We applied these approaches to conceptions of left–right labels in Japan, where the primary issue of elite-level conflicts has been distinctive compared with other developed countries. We found that, on average, while Japanese voters understand policy-related meanings of “left” and “right,” they primarily associate these labels with security and nationalism, and, secondarily, with social issues; they do not associate these labels with economic issues. Voters’ understandings partly depend on their birth cohort, but observed patterns do not necessarily coincide with what many researchers would predict regarding generational differences in Japanese politics. Mixture model results suggest that some individuals tend to associate left–right labels with security and nationalism policies, while others link them to social policies. Over one-third of respondents seemed to barely understand the usage of left–right labels in policy positions. Our study improves upon existing methods for measuring voter understanding of ideological labels, and reconfirm the global diversity of meanings associated with left–right labels.

This paper examines the relationship between policy preferences, issue importance, and vote choice in the 2021 Japanese general election using online survey data collected in February 2022. Regarding policy preferences, unsupervised classification was applied to the integrated data of a candidate survey and this study’s survey, and the respondents were grouped into nine clusters. The results suggested that, though few people supported the Liberal Democratic Party (LDP)’s positions broadly, the LDP obtained votes mainly from conservative voters on security and nuclear power issues, while liberal oppositions failed to garner votes from voters with policy preferences close to theirs. Regarding issue importance, the author conducted a conjoint experiment to determine which issues were important to each respondent. The results revealed that not only security and nuclear power but also consumption tax and same-sex marriage were important; furthermore, the latter issues were more important than the former.

To better understand the nature of American mass party identification, it is crucial to examine how voters understand terms used in measuring partisanship in public opinion surveys, such as “Democrat” and “Republican.” For this purpose, we conducted a conjoint experiment where respondents evaluated hypothetical profiles’ partisanship. We show that, in contrast to previous studies which rely on one theoretical perspective to understand mass partisanship, multiple theories are reflected in how voters understand labels representing their partisanship. Further, the results suggest that many Americans seem to equate party identification with vote choice, contrary to standard assumptions in American political behavior research that these are separate concepts.

We contribute to the demand-side theory of women’s underrepresentation in democracy, by which we mean that women are underrepresented in politics because voters prefer male politicians, by focussing on gender’s effect on the persuasive power of politicians’ policy statements. We conducted a survey experiment in Japan, where women are seriously underrepresented in politics and voter preferences for individual candidates matter with respect to women being elected. We showed participants fictitious local legislators’ policy statements and asked to what extent they supported those statements. We selected foreign and welfare issues on which voters have shared gendered stereotypes and randomly manipulated the legislators’ gender, ideological positions, and tone of their statements. We found no significant differences in approval for policy statements between female and male legislators. This result holds irrespective of legislators’ ideological positions and tone of the statements. We infer from the results of factual manipulation checks that such null results are attributable to the low rate of respondents who recognized the fictitious legislators’ gender. Although our study is preliminary, and its results are ambiguous, our experimental design helps scholars disentangle some mechanisms of voters’ underappreciation of female politicians.

Why do citizens prefer high-skilled immigrants to low-skilled immigrants? To understand the causal mechanism behind this tendency among citizens, we conducted a vignette survey experiment that enables us to clarify the role of multiple mediators. We specifically focused on three key factors that have been proposed in existing research as those that could lead citizens to welcome high-skilled immigrants: expectations of economic contribution, welfare contribution, and small crime potential. We found that the skill premium was fully eliminated when natives were informed that immigrants would be engaged in low-skill jobs in the host country, which underscores the essential role that post-migration work plays in the acceptance of immigrants by natives. Our findings provide suggestive evidence that natives welcome high-skilled immigrants simply because they expect economic benefits from high-skilled immigrants, not because they expect them to contribute to welfare or be less likely to commit crimes.

Although measuring the ideal points of news media is essential for testing political communication theories based on spatial theory, prior methods of estimating ideal points of media outlets have various shortcomings, including high cost in terms of time and human resources and low applicability to different countries. We propose that unsupervised machine learning techniques for text data, specifically the combination of a text scaling method and latent topic modeling, can be applied to estimate ideal points of media outlets. We applied our proposed methods to editorial texts of ten national and regional newspapers in Japan, where prior approaches are not applicable because newspapers have never officially endorsed particular parties or candidates, and because high-quality training data for supervised learning are not available. Our two studies, one of which analyzed editorials on a single typically ideological topic while the other investigated all editorials published by the target papers in one year, confirmed the popular view of Japanese newspapers’ ideological slant, which validates the effectiveness of our proposed approach. We also illustrate that our methods allow scholars to investigate which issues are closely related to the respective ideological positions of media outlets. Furthermore, we use the estimated ideal points of newspapers to show that Japanese people partially tend to read ideologically like-minded newspapers and follow such newspapers’ Twitter accounts even though their slant is not explicit.

This study examines how politically mature Japanese adolescents are compared to adults and how political maturity increases in adolescence, focusing on the ideological consistency of issue attitudes and partisanship as a measure of voter competence. We conducted a pair of online surveys, one of which was for 15- to 22-year-olds and the other for the entire electorate, in 2017, and asked respondents their opinions about a variety of issues related to the left–right ideology. We analyzed the proportions of ideologically consistent attitudes using Dirichlet regression. The results indicated that, although young people have less ideologically consistent issue attitudes than older people, adolescents’ attitudes are more consistent than chance levels at the age of 15 and their consistency increases in adolescence. We also investigated the ideological proximity of partisanship by combining our data and that from an elite survey of the 2017 general election. The estimates of the sample-selection ordered probit model tell us that, among those who have partisanship, adolescents attach to parties that are ideologically close to them in the same manner as adults. Our results have implications for the discussion on lowering the voting age in Japan.

This study investigates the transition of postwar Japanese public opinion on constitutional revision by comprehensively analyzing the results of opinion polls on the constitution conducted by seven major polling institutes. A “pooling the polls” method, derived from a dynamic linear model, allows us to estimate the latent approval and disapproval rates for constitutional revision in consideration of variations in question items and wording, house and mode effects, and sampling errors. The results imply that, while voters perceived “full revision” of the constitution as a political issue in the 1950s, they came to consider Article 9 as the most important problem by far after the 1960s. We also find that citizens became clearly aware of issues other than Article 9 in the 1990s and 2000s, and that they focused on the problem of Article 9 again, following the Koizumi administration. Moreover, the effects of question items and wording suggest that voters regard the second (but not the first) paragraph of Article 9 as a political issue, and that priming respondents with questions containing the word “war” increases the disapproval rate for the revisions in Article 9.

This study investigates value preferences and structures among Japanese voters and political candidates. Voters were surveyed after the 2014 Lower House election, while political candidates were surveyed before the 2016 Upper House election. To measure their value preferences, respondents were asked to rank seven values: freedom, equality, economic stability, morality, self-reliance, social order, and patriotism. Statistical analyses reveal substantially different value priorities between voters and candidates. Furthermore, although little distinctiveness in value preferences was observed among Japanese voters, the tendency and cohesion of value preferences among candidates varied across parties. More specifically, the four opposition parties that collaborated in the 2016 election and the Clean Government Party had similar value preferences, while the least cohesive party in terms of value preferences was the Liberal Democratic Party.

Scholars have recently argued that prime ministers reshuffle their cabinets strategically. Although some scholars assume that cabinet reshuffles help prime ministers increase their government’s popularity, this assumption has not been tested formally because of the endogeneity problem. In Japan, polling firms sometimes provide respondents with cues about a reshuffle when asking about cabinet approval following reshuffles, while others do not. I utilized this convention in the Japanese media to test the assumption that reshuffles increase cabinet approval ratings. Applying a dynamic linear model to pooled poll data from 2001 to 2015, I achieved high internal, external, and ecological validity. The analyses show that cues about reshuffles increase cabinet approval ratings by 2.4 percentage points on average, and the credible interval of the effect does not include zero. This result reinforces the findings of previous research on the theory of cabinet management.

This study estimates the ideology of Japanese politicians, political commentators, political parties, and news media using Twitter data. While previous studies have utilized various methods to measure the ideology of political actors, the method using Twitter data has many advantages, one of which is that we can estimate the ideology of local politicians and political commentators. The statistical model adopted here assumes that general Twitter users prefer to follow the accounts of political actors whose position is close to theirs and estimates the ideal points of both the political actors and general users based on whether or not the general users follow the accounts of the political actors. I estimated the ideological positions of 70 members of the House of Representatives, 46 members of the House of Councillors, 10 parties and other political institutions, 6 newspaper companies, 39 local politicians and former politicians, and 41 political commentators. The estimation results can be considered to be valid because Twitter-based ideal points of the Diet members are highly correlated with their positions estimated by data from an elite survey.

The partial observability probit model is a statistical model for discrete outcomes caused by a complex combination of multiple latent factors. It is useful for political science research because political scientists often study interactions of unobservable decision making by several actors or survey responses resulted from a mixture of psychological factors, and because outcomes are recorded as a discrete variable in many cases of political science. I introduce this model as well as its underlying models, and its application and extension in political science literature. In addition, I developed an applied model with partial observability for the study of the survey responses on ideological self-identification. Ideological self-identification is measured by where a respondent place oneself on a discrete ideological scale, and can be decomposed into three latent factors: recognition, extremity, and direction. The new model can be estimated by Markov chain Monte Carlo methods. I applied my model to Japanese opinion poll data. An information criteria judged my model was superior to the previous ones, and I found some results that could not be led by the previous models.

Ever since Philip Converse's prominent work in the field, the viewpoint that ideological thinking represents the political sophistication of the electorate has become predominant. Ideology is, however, an essential requirement for uninformed voters, considering its heuristic role. Therefore, I hypothesize that ideological consistency tends to be low among people with high or low levels of political knowledge, whereas high consistency is observed among those with average political knowledge. Additionally, I argue that this hypothesis has particular relevance in contemporary Japan. Using an index that measures ideological consistency at the individual level, I examine data from three Japanese opinion polls conducted in the 2000s. The results support my hypothesis by showing that ideological consistency across issues statistically and substantially fluctuate according to voters' levels of political knowledge, forming a curvilinear relationship. This finding facilitates the rethinking and redefining of political sophistication.