Survey data suggest that cropsharing contracts exhibit a much higher degree of uniformity than is warranted by economic fundamentals. We propose a dynamic model of contract choice to explain this phenomenon. Landowners and tenants recontract periodically, taking into account expected returns as well as conformity with local practice. The resulting stochastic dynamical system is studied using techniques from statistical mechanics. The most likely states consist of patches where contractual terms are nearly uniform, separated by boundaries where the terms shift abruptly. These and other predictions of the model are borne out by survey data on agricultural contracts in Illinois.

New ideas, products, and practices take time to diffuse, a fact that is often attributed to some form of heterogeneity among potential adopters. This paper examines three broad classes of diffusion models—contagion, social influence, and social learning—and shows how to incorporate heterogeneity into each at a high level of generality without losing analytical tractability. Each type of model leaves a characteristic “footprint” on the shape of the adoption curve which provides a basis for discriminating empirically between them. The approach is illustrated using the classic study of Ryan and Gross (1943) on the diffusion of hybrid corn.

We propose a model to study when an intermediate action can serve as a stepping stone that enables the elimination of a harmful norm. While the intermediate action may facilitate the first “step,” it may also become a new norm. We derive intuitive conditions for stepping stones, which depend on the relative size of social penalties and intrinsic utility benefits. We propose an econometric approach to testing whether an intermediate action is a stepping stone, and apply it to original data on female genital cutting in Somalia. The analysis shows that the intermediate action may become the new norm.