Social capital works on whole networks and its process (chance of investment and return) is structured along with the configuration of them. However, in an ordinary survey design, it is quite difficult to locate respondents' personal networks on such macro configurations. Here we introduce a concept of whole-net base. It is as a shared attribute that indicates a latent whole network behind it. Keeping contact with a schoolmate, for example, indicates that the tie is a part of a whole network that consists of latently all graduates of the school. Under a question how social capital is built in the stratification process, we analyze a personal network data from the viewpoint of investment-return through various friends-net bases. The results show that; 1) the upper stratum invests and gets return more than the lower, especially on job-net and school-net bases that directly correspond to socio-economic status, however, 2) it is the lower stratum in which efficient investment (the tendency that more investment correspond to more return) is observed clearly, moreover, the observation is not limited to the specific whole-net base. These suggest a dynamic opportunity structure of social capital: while it reinforces the advantageous socio-economic positioning for the upper stratum, at the same time, it also makes their life chances greater for the lower stratum. However, we have to pay attention to those elder people in the lower of lower strata who do not have any access to social capital.

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In this paper, we focused on trust as one of the factors of social capital, and examined its generating processes by comparing two main theoretical approaches of trust — the Emancipation Theory of Trust and the Reduction Approach. The former theory states that creation of general trust will be undermined when commitment relations with specific others are strong, whereas the latter approach states that strength of commitment relations with specific others provides the basis for nurturing general trust. First we examined the relationship between city size (supposedly an indicator of the strength of committed relations) and the level of general trust using data from two social surveys conducted in Japan. The result of the analysis showed no correlation between city size and the level of general trust. Then we performed structural equation modeling to explore the relationships between a wider variety of capitals, social resources and general trust. The results of the analyses show that general trust is nurtured when it is based on relations of trust with specific people. In other words, the result is diametrically opposed to the Emancipation Theory of Trust in that it implies that placing a high priority on existing relationships with people fosters accumulation of general trust and therefore of social capital.

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It is empirically verified that people with higher income are, on an average, more trustful than those with lower income. If this finding is unconditionally valid, a dismal society may emerge and lead to the rich becoming richer by trusting strangers and receiving higher payoffs. The purpose of this paper is to explore the conditions that facilitate or hinder the growth of a dismal society by developing an agent-based model. We examined the hypothesis that the attractiveness of the market facilitates the trusting behavior of the rich, which results in a wider gap of the accumulated payoffs between the rich and the poor. In the model, agents decide whether or not they should leave their assurance group in order to receive a higher payoff from a stranger in the market. If an agent's partner is trustworthy, the agent receives a higher payoff from the partner than from a member in his/her assurance group. However, if the partner is not trustworthy, the agent receives a lower payoff. After receiving payoffs, agents learn to modify their behavior. The result of the simulation reveals that the gap between the rich and the poor widens only in the case of a moderately attractive market.

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In this paper, we discuss one of the major factors in social capital, the issue of trust, in terms of detection of trustworthiness of others. Yamagishi's Emancipation Theory of Trust concluded that high trusters, or people who have a high level of general trustfulness toward others, have social intelligence to accurately detect the general character of others. Kikuchi, Watanabe, and Yamagishi's Detection Experiment provided the empirical basis of such a conclusion. However, the Prisoner's Dilemma (PD) Game adopted in the Detection Experiment did not necessarily use appropriate alternatives of behaviors for participants as indicators of the general characters of people. Consequently, the results from the experiment are not appropriate for reviewing the ability to “detect a particular person's general character.” In order to overcome such problems and to measure the ability to detect a person's trustworthiness more appropriately, we conducted a laboratory experiment by adopting the game of enthronement. After a series of analyses, we could not confirm such a relationship between trustfulness and the ability to detect trustworthiness as discussed in a series of studies by Yamagishi. On the other hand, after reviewing the relationship between breadth of beliefs about others and the ability to detect trustworthiness of others based on Kelley and Stahelski's Triangle Hypothesis in a traditional PD game study, we could confirm that it is a person's assumptions or beliefs about internalization of social norms by others that determine the accuracy of his/her ability to detect trustworthiness of others.

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For the last two decades, there has been a growing argument that “social capital” derived from human relationships has an influence on various aspects of social phenomena. In many such studies, it is pointed out that social capital has two aspects social relationships as “network” and “trust” associated with such relationships. However, there has been a tendency for them to be discussed separately and they have not been integrated into one concept of social capital.
In this paper, we would like to define the ‘tie’ of human relationships and ‘strength of tie’ among the component concepts of social capital in a formal manner, and try to define the ‘trust’ mechanism as a function that maps ‘one's act counting on other people's actions’ into its feasibility. We will then explore the empirical credibility of such formalization by analyzing survey data.
In the following two sections, we will make clear related problems. First, we try to distinguish the ‘feasibility of one's acts which count on other people's actions’ from the probability of other people's action. In our view, one will never calculate an expected utility using the probability of other people's actions in everyday life. He/she will only judge whether his/her act counting on other people's actions is feasible or not. In the next section, we will distinguish the ‘trust’ mechanism from the ‘confidence’ mechanism according to Luhmann. We see their difference as a difference in domain of feasibility that each mechanism concerns.

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Mathematical sociology as one of subfields of sociology is an empirical science. Under this basic idea, this article tries to address the unsolved problem of FK model (Fararo and Kosaka 2003), that is, verification of the model. Specifically, we indicate that result of verification depends on the assumption of “objective stratification system,” the initial conditions of the model. Furthermore, we study this tendency theoretically. By passing through the strict examination about verification of the model, we will be able to develop FK model as well as mathematical sociology itself.

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Hamada and Ishida (2003) formulated the Virtual Regulation Analysis for Inequality of Opportunity, based on Roemer's idea, equality of opportunity principal. This analytical method enables us to measure the degree of inequality under the virtual state that inequality of opportunity, such as sex or his/her parents' status, is regulated. However, the assumptions of their model were ambiguous and their method did not take into account the way of testing statistical significances for the difference of Gini coefficients between before and after virtual regulation of opportunity.
In this article, we clarify the differences between Roemer's model and Virtual Regulation Analysis and propose a method of statistical significance test for the difference of Gini coefficients between before and after the regulation. In order to compute a standard error of Gini coefficient, we use Efron's bootstrap method. We also present some examples of analysis with SSM 1985 and 1995 data. Furthermore, we discuss the methodological problem about the partition of the data of achievement level and give one theoretical answer. As one of applications of our method, we analyze the effect of inequality of opportunity as to the amount of inherited immovable property on the amount of family immovable property and family income corresponding to different numbers of partition intervals.

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