Carlos Rodríguez-Sickert

The dynamics of a mobile phone network

The empirical study of network dynamics has been limited by the lack of longitudinal data. Here we introduce a quantitative indicator of link persistence to explore the correlations between the structure of a mobile phone network and the persistence of its links. We show that persistent links tend to be reciprocal and are more common for people with low degree and high clustering. We study the redundancy of the associations between persistence, degree, clustering and reciprocity and show that reciprocity is the strongest predictor of tie persistence. The method presented can be easily adapted to characterize the dynamics of other networks and can be used to identify the links that are most likely to survive in the future.

To Each According to its Degree: The Meritocracy and Topocracy of Embedded Markets

A system is said to be meritocratic if the compensation and power available to individuals is determined by their abilities and merits. A system is topocratic if the compensation and power available to an individual is determined primarily by her position in a network. Here we introduce a model that is perfectly meritocratic for fully connected networks but that becomes topocratic for sparse networks-like the ones in society. In the model, individuals produce and sell content, but also distribute the content produced by others when they belong to the shortest path connecting a buyer and a seller. The production and distribution of content defines two channels of compensation: a meritocratic channel, where individuals are compensated for the content they produce, and a topocratic channel, where individual compensation is based on the number of shortest paths that go through them in the network. We solve the model analytically and show that the distribution of payoffs is meritocratic only if the average degree of the nodes is larger than a root of the total number of nodes. We conclude that, in the light of this model, the sparsity and structure of networks represents a fundamental constraint to the meritocracy of societies.

The Political Economy of School Size: Evidence from Chilean Rural Areas

Public schools in Chile receive a per-student subsidy depending on enrollment, and are managed by local governments that operate under soft budget constraints. In this paper, we study the effects of this system on per-student expenditures. Per-student expenditures on rural areas are 30% higher than in urban areas. We find that about 75% of this difference is due to the fact that rural public schools are significantly smaller and thus do not benefit from economies of scale. Besides, we also show that in our preferred estimates about 50% of the students in rural areas could be moved to schools that could exploit economies of scale – i.e., these students could attend bigger schools traveling at most an hour day a day in total. We show that even if we use conservative average speed rates or control for transportation, utility and infrastructure costs, there is a sizeable share of students that could be consolidated. We argue that local governments that have soft budget constraints do not consolidate these schools giving the existing potential because of political factors: closing schools is harmful for mayors in electoral terms. Consistent with this claim, we find that a decrease in the degree of political competition in areas with better access to non-voucher transfers from the central government (i.e. with softer budget constraints) decreases the extent of the inefficiency.

The Evolution of Moral Codes of Behavior

Within a standard stochastic evolutionary framework, we study the evolution of morality, both at the level of behavior and at the level of codes of behavior. These moral codes involve sanctioning deviant agents. We provide conditions under which the presence of any small degree of inter-group selection allows the emergence of moral codes which improve social efficiency. The result depends on both the efficacy of the available sanctioning technology and on the ratio of the number of members which societies are composed of to the number of societies in conflict. Group-level mutations (influential leaders, religion and collective deliberative process) can work as an inducement to the evolution of morality. We also consider the possibility that a moral code involves rewards rather than sanctions. Although no system of rewards will evolve, we show that its presence can facilitate the emergence of a sanctioning code.