Interaction, Adaptation, and Social Structure

这项研究项目关注的是主体向邻居学习或适应其行为的动态过程，以及由此产生的空间整合模式。这种类型的进程涵盖了各种各样的现象，包括新技术的传播、社会规范的传递以及按阶级、种族或民族分类。这项研究扩展了我们对这种过程的理论理解，并在可能的情况下将理论预测与证据进行了比较。主要研究了三个问题。首先是这些过程的宏观行为与规范个体行为的微观反应规则之间的关系。这个假设是，某些长期属性，如各种均衡和非均衡模式的相对可能性，在不同规格的个人适应行为下是稳健的。这将提高这类模型在个别反应规则不同且难以统计估计的应用中的有用性。理论研究的第二个主题是局部相互作用过程的惯性--系统从任意初始状态达到(或接近)长期运行条件所需的预期时间。扩展这一领域的前人工作，将显示惯性如何与社会网络的几何属性相关。特别重要的是代理人在小而紧密的群体中相互作用的程度，而不是大的、不同的群体。研究的第三部分根据经验证据测试这些理论的某些定性预测。主要的应用是对委托-代理合同农业的实证研究，使用了一个涵盖1977-1995年间伊利诺伊州数千个农场的广泛数据库。这些数据的详细程度为检验理论提出的各种假说提供了一个独特的机会。一种假设是，合同条款倾向于表现出局部一致性效应，即它们围绕着可以被解释为局部规范的某些价值观。一旦确立，这些规范就塑造了缔约各方的期望，并因此倾向于通过先例的力量使自己永久化。这一规范形成模型导致了对合同条款的空间和时间变化的具体预测，这些预测可以得到经验检验。该理论提出的第二个假设是，这些规范可能导致新古典价格均衡的可衡量扭曲，即它们在预期中创造了粘性，阻碍了要素回报的平衡。这项研究的总体目标是确定局部相互作用的动态模型导致不同于新古典均衡模型的预测的情况，并对其中一些预测进行实证检验。

This research project is concerned with dynamic processes in which agents learn from or adapt to the actions of their neighbors, and the spatial patterns of conformity that result. Processes of this type cover a wide variety of phenomena, including the diffusion of new technologies, the transmission of social norms, and sorting by class, race, or ethnicity. The research extends our theoretical understanding of such processes, and where possible compares predictions of theory with evidence. Three topics are investigated. The first is the relationship between the macroscopic behavior of these processes and the micro-response rules governing individual behavior. The hypothesis is that certain long-run properties, such as the relative likelihood of various equilibrium and disequilibrium patterns, are robust under various specifications of individuals' adaptive behaviors. This would enhance the usefulness of such models in applications where individual response rules are heterogeneous and difficult to estimate statistically. A second topic of theoretical investigation is the inertia of local interaction processes --the expected time it takes the system to reach (or come close to) long-run conditions from an arbitrary initial state. Extending previous work in this area, it will be shown how inertia is related to geometric properties of the social network. Of particular importance is the degree to which agents interact in small, close knit groups instead of large, disparate ones.The third part of the research tests certain qualitative predictions of these theories against empirical evidence. The primary application is an empirical study of principal-agent contracts agriculture, using an extensive data base covering several thousand farms in Illinois from 1977-1995. The level of detail in these data presents a unique opportunity to test various hypotheses suggested by theory. One hypothesis is that contract terms tend to exhibit a local conformity effect, that is, they cluster around certain values that can be construed as local norms. Once established, these norms shape the expectations of the contracting parties, and thus tend to perpetuate themselves through the force of precedent. This model of norm formation leads to specific predictions about spatial and temporal variations in contract terms that can be tested empirically. A second hypothesis suggested by the theory is that such norms can cause measurable distortions from neoclassical price equilibrium, that is, they create a stickiness in expectations that impedes the equilibration of factor returns. The overall goal of the research is to identify situations where dynamic models of local interaction lead to predictions that differ from those of neoclassical equilibrium models, and to put some of these predictions to the test empirically.