In my paper, which got the best paper award, I challenged to unravel the mechanism in which people help each other in loose-knit organization. Firstly, I carried out empirical research on the helping activities in the individual affiliate labor unions, called community unions. Then I represent the focal phenomenon by the mathematical model to analyse the mechanism of it. The importance of this paper is twofold. One is that I focused on the contemporary problem such as human cooperation in flexible relationships. The other is that I combined the mathematical analysis with the empirical research in order to explain the focal phenomenon. In this paper, putting the more emphasis on the latter issue, I would argue the impact of this multi-method approach on only the mathematical sociology but also the sociology as a whole.

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     In this study, I aim to clarify the social mechanism of the self-fulfilling prophecy in statistical discrimination against women that female applicants are confronted with in their job searches. The analyses using a simple formal model reveal the following result: In a society where workers cannot achieve work-life balance, so much so that dual-career families have lower well-being than single-earner families, if the ratio of job openings to applicants is less than one, then employers' statistical discrimination based on the belief that women are more likely than men to give up their careers consequently causes the probability of women' s early retirement to be higher than that of men's retirement, which eventually reproduces the statistical fact that women's turnover is higher than men's. Next, on the basis of this result, I try to specify the socio-economic factors that make employers choose the equal treatment of men and women, rather than discriminatory treatments. By considering the meaning of these factors, we can clearly understand how diversity policies such as the improvement of work-life balance and the implementation of work-sharing can stop the repetition of statistical discrimination.

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     This article proposes a tool for describing historical changes as interactions between influential leaders' choices and public sentiment. For this purpose, I first point out another type of micro-macro linkage for social change that complements the type of micro-macro link described by Coleman's boat. Second, I propose an “initial condition game” of Richardson's arms race model as a concrete example of the above framework. The initial condition game represents an interdependent rational choice situation for influential players on the premise of public sentiment. In terms of the mathematical analysis of arms race and armed conflict, the initial condition game can be regarded as an attempt to integrate deterministic differential equation models with the strategic game theoretic models of arms races. Several cases of the initial condition game are analyzed as exemplars.

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     The purpose of this article is to clarify the relationship between the emergence of institutions and the dynamics of groups, focusing on the institution for helping in community unions. As previous works pointed out, helping behavior in community unions is the exchanges based on downward indirect reciprocity. Due to the time-gap of this exchange, the maintenance of the helping behavior requires the development and stability of the group. At the beginning of the unions where the members apparently have small incentives, how the institution for cooperation can emerge? On the other hand, we observed protest activity (institution) promote people to join the community unions. Thus we attempt to analyse the interdependence between the emergence of the institution and group dynamics. For this goal, we present a game theoretical model including the dynamically change in group size and the behavior of players, applying“group reputation effect”. This analysis shows that if contribution of players has an important role for increasing in the group size, the initial players have incentives to engage in the volunteer activities (purely other-regarding behavior) for the group.

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     Participant observation has revealed the phenomenon of“relay between affected areas,”which means that those who receive help after experiencing a natural disaster support others who are subsequently affected by a different disaster. This behavior is equivalent to a form of“generalized exchange”advanced by C. Lévi-Strauss. However, the presence of this phenomenon has not been substantiated by an empirical analysis. Using nationally representative data on Japanese citizens, this paper investigates whether the volunteering that occurred following the Great East Japan Earthquake had the nature of a generalized exchange.
     The main findings of this study are as follows. First, the experience of receiving help positively influences disaster response volunteering. Second, in areas with lower risk of disaster, the association between receiving help and subsequently volunteering in devastated sites strengthens. These results suggest both that the volunteering that occurred after the Earthquake resembles a generalized exchange and that“unexpected kindness (On)”received in regions that rarely experience disasters promotes a generalized exchange.

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     The purpose of this study is to clarify how the increase in the number of members of a group affects cooperation. Most of the previous works focused on static one-shot games. This study, however, focuses on repeated games, more specificlly stochastic/dynamic games that enable us to analyze games in which the number of players changes, especially becomes larger, by degrees. In addition, we do not assume a simple way to increase in the number of players but assume Group Reputation Mechanism (hereafter GRM) in which the number of cooperating players in the group in the previous game affects how many players outside the group join the group. We find that GRM, in which the number of new members is proportion to the number of players who cooperate in the previous game, allows players to cooperate without any sanction in the pure collective goods which are characterized non-excludability and non-rivalness.

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     The effects of neighborhood environments on satisfaction with the neighborhood among Japanese were investigated. Multilevel analyses were used to predict the effects of individual-level evaluations of neighborhood environments including social cohesion, neighborhood disorder, and perceived crime victimization, as well as community-level evaluations that aggregated survey responses for neighborhoods (cho-chomoku). Data were obtained from a probability sample survey of 4,676 men and women aged 25 years and older living in 30 municipalities of Tokyo, Chiba, Kanagawa and Saitama prefectures of Japan. The results indicated the following. (1) At the individual-level evaluation of neighborhoods, respondents perceiving high social cohesion showed significantly higher satisfaction with the neighborhood. At the community-level, high aggregate social cohesion was associated with higher levels satisfaction with neighborhood. (2) At the individual-level evaluation of neighborhoods, respondents perceiving high neighborhood disorder showed lower satisfaction with neighborhoods. A significant cross-level interaction effect between individual and community-level evaluation of neighborhood disorder was observed, suggesting that effect of individual-level evaluation on satisfaction was greater for neighborhoods with higher disorder. (3) At the community-level, high aggregate perceived crime victimization was associated with lower levels satisfaction with neighborhood.

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     The relationship between social structure and individual behavior has been one of the fundamental issues of sociology. The“Coleman Boat”is a pertinent formulation of the cause and effect relationship between social structure and individual behavior. This paper constructs a differential geometric model of the Coleman Boat through representing social structure as a manifold and individual behavior as a differential form. At this time, methodological collectivism, where social structure is considered to regulate individual behavior, and methodological individualism, where individual behavior is considered to regulate social structure, can be seen as the functors between the social structure category, the macro category, and the individual behavior category, the micro category. This allows us to demonstrate, using Stokes' theorem regarding the integral of differential forms on a manifold, that the macro and micro categories are equivalent, and thus conclude that methodological collectivism and methodological individualism are both correct and equivalence.

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