Meet, discuss, and segregate!

We present a model of opinion dynamics in which agents adjust continuous opinions as a result of random binary encounters whenever their difference in opinion is below a given threshold. High thresholds yield convergence of opinions toward an average opinion, whereas low thresholds result in several opinion clusters. The model is further generalized to network interactions, threshold heterogeneity, adaptive thresholds, and binary strings of opinions. ᭧ 2002 Wiley Periodicals, Inc. T he present work was initially motivated by an empirical study about the diffusion of environmentally friendly practices (agri-environmental measures) among European farmers [1]. From 1992 Common Agricultural Policy (CAP) of European Communities was changed from the postwar policy of financially supporting production to a financial support of environmentally friendly practices such as input (fertilizers and pesticide) reduction, set-aside, and preservation of biodiversity. The next problem was the implementation by farmers of the policy defined at the highest level, the European Commission. Our " IMAGES " teams then studied the factors and processes, which favor (or prevent) the adoption by farmers of the new policy. The empirical data collected through surveys and interviews with farmers and agricultural counselors are in accordance with previous literature on the Sociology of Agriculture [2] and demonstrate that: ● changing practices involves a lot of uncertainties for the farmer; for instance, fertilizers reduction combined with best farming practices might imply a complete reorganization of crop choice and annual rotation. ● To decrease uncertainties, farmers engage in many discussions with their peers; in addition to the propagation of information, the interactions between farmers perform a normative control and a prestige allocation. The nor-mative control is based on an agreement about what constitutes 'good' or 'bad' farming practices. ● The specific interviews done in our project showed that the decision of adopting an agri-environmental measure is the result of a process, which involves social and infor-mational influences, sometimes during several years (for more information about the interviews and data see Deffuant [3]).