Essays on economic and social complexity

The multidisciplinary approach to problem solving involves drawing appropriately from different viewpoints to redefine problems outside of normal boundaries and reach solutions based on a new understanding of complex situations. Social and economics science have always borrowed and embraced tools and instruments from mathematics and physics to develop their theories. Historically a real multidisciplinary methodology to economic and social issues has been neglected by the academic researchers due to a widespread gap in their formal approach. Recently a new interdisciplinary framework has been developed connecting together social and economics theories with the complex systems analysis; this approach reveals new conceptual prospectives and methodologies thanks to its multiple-level viewpoint, which are able to disclose novel challenges and problems. This thesis collects three different multidisciplinary approaches to social and economic behaviors formalized with the complex systems tools. Chapter 2: We introduce a statistical agent based model to describe the phenomenon of drug abuse and its dynamical evolution at the individual and global level. The agents are heterogeneous with respect to their intrinsic inclination to drugs, to their budget attitude and social environment. The various levels of drug use were inspired by the professional description of the phenomenon and this permits a direct comparison with all available data. We show that certain elements have a great importance to start the use of drugs, for example the rare events in the personal experiences which permit to overcome the barrier of drug use occasionally. The analysis of how the system reacts to perturbations is very important to understand its key elements and it provides strategies for effective policy making. The present model represents the first step of a realistic description of this phenomenon and can be easily generalized in various directions. Chapter 3: We characterize the statistical law according to which Italian primary school-size distributes. We find that the schoolsize can be approximated by a log-normal distribution, with a fat lower tail that collects a large number of very small schools. The upper tail of the school-size distribution decreases exponentially and the growth rates are distributed with a Laplace PDF. These distributions are similar to those observed for firms and are consistent with a Bose-Einstein preferential attachment process. The body of the distribution features a bimodal shape suggesting some source of heterogeneity in the school organization that we uncover by an indepth analysis of the relation between schools-size and citysize. We propose a novel cluster methodology and a new spatial interaction approach among schools which outline the variety of policies implemented in Italy. Different regional policies are also discussed shedding lights on the relation between policy and geographical features. Chapter 4: By analyzing the distribution of revenues across the production sectors of quoted firms we suggest a novel dimension that drives the firms diversification process at country level. Data show a non trivial macro regional clustering of the diversification process, which underlines the relevance of geopolitical environments in determining the microscopic dynamics of economic entities. These findings demonstrate the possibility of singling out in complex ecosystems those microfeatures that emerge at macro-levels, which could be of particular relevance for decision-makers in selecting the appropriate parameters to be acted upon in order to achieve desirable results. The understanding of this micro-macro information exchange is further deepened through the introduction of a simplified dynamic model.