THE ROLE OF NETWORKS IN COLLECTIVE ACTION WITH COSTLY COMMUNICATION.

Individuals frequently contribute their resources voluntarily to provide public goods. This paper models the manner in which the linkage between members in a community influences the likelihood of such actions through spontaneous activism in networks. The model I use abstracts from the issue of free-riding behavior by means of small deviations from standard preferences. Instead, it concentrates on the communication aspect of provision through collective action. The solution concept is Nash equilibrium. I find that the likelihood of efficient provision of a discrete public good in random social networks increases very rapidly for parameter values where the network experiences a phase transition and large-scale decentralized activism becomes feasible. As a result, the model shows that successful coordination may be more readily achieved the larger the population is, provided its members are sufficiently connected. In contrast with previous results in the literature, this results holds even as the size of the population increases without bound, and it is consistent with the existence of largescale activism in large populations.Collective Action

Natural disasters and growth: evidence using a wide panel of countries

Large natural disasters (LNDs) are ubiquitous phenomena with potentially large impacts on the infrastructure and population of countries, and on their economic activity in general. I examine the occurrence pattern of several types of disasters on a panel of 113 countries and its relationship with economic growth using data ranging from 1960 to 1996. The disasters are earthquakes, floods, slides, volcano eruptions, tsunamis, wind storms, wild fires and extreme temperatures. The country sample is partitioned in two ways: small, medium and large population; and low, medium and high income. The results suggest a heterogeneous pattern of short and long-term impact of LNDs, depending on the per capita GDP, the size of the countries studied and the type of LND. Overall, and contrary to previous research, LNDs appear to have persistent effects on the rate of GDP growth in the period between 1960 and 1996. These effects range from a decrease of 0.9% to an increase of 0.6%, depending on the type of disaster.Natural disasters, catastrophes, growth, foreign aid, panel data

Evaluation of a prebiotic and an organic acid-supplemented diets on the performance and allometric parameters of broiler chickens with controlled feeding

P?ginas 52-66El prop?sito de esta investigaci?n fue evaluar el efecto de un ?cido org?nico (?cido fum?rico), un prebi?tico comercial (Fortifeed?) y la mezcla de estos dos frente a un antibi?tico promotor de crecimiento (Bacitracina de Zn) con alimentaci?n controlada en los par?metros productivos y crecimiento alom?trico del tracto gastrointestinal de pollos de engorde durante 42 d?as. Se evaluaron cinco tratamientos: control sin aditivos, control con Bacitracina de Zn (0,3 g/kg), con ?cido fum?rico (5 g/kg), prebi?tico (0,6 g/kg) y la mezcla del ?cido org?nico y el prebi?tico en pollos de engorde machos de la estirpe Cobb. Se aplic? un ANOVA de una v?a, utilizando el software InfoStat. No se encontraron diferencias estad?sticas en el consumo de alimento entre tratamientos. Las mejores conversiones alimenticias (p < 0,05) fueron para el antibi?tico (1,88) y la mezcla de aditivos (1,89). La alimentaci?n controlada redujo el peso promedio a la primera semana, el cual pudo tener incidencia en menores pesos al sacrificio. No se encontr? diferencias en el rendimiento en canal y mortalidad. Los m?rgenes de ingreso fueron superiores para el tratamiento con antibi?tico (14,12%) y menores en el control (8,31%).Las constantes de crecimiento alom?trico del h?gado y yeyuno en los tratamientos con aditivos fueron superiores (p < 0,05) al control. Los valores de pH del ?leon fueron inferiores (p < 0,05) en el tratamiento con ?cido org?nico y la mezcla de aditivos comparados con los otros tratamientos. Se concluye que la mezcla de aditivos ejerci? un efecto sin?rgico en los par?metros productivos.ABSTRACT. The objective of this research was to evaluate the effect of an organic acid (fumaric acid), and a commercial prebiotic (Fortifeed?), or a combination of both the organic acid and the prebiotic in front of the effects of an antibiotic (Zn Bacitracine), on the productive performance and allometric growth of the gastrointestinal tract in broiler chickens Cobb, during an experimental period of 42 days. Five treatments were evaluated: negative control diet with no additives, positive control diet with Zn Bacitracin (0.3 g/kg), diet with Fumaric acid (5 g/kg), diet with Prebiotic (0.6 g/kg) and a diet with a mixture of both the prebiotic and the organic acid. The data were analysed using InfoStat software program by one-way analysis of variance, and significant differences between treatments were determined by Tukey test (p<0.05). There were no differences in feed intake. The combination of the prebiotic and the organic acid showed the higher feed conversion (1.89), followed by the antibiotic (1.80) treatment when compared to the organic acid-treated controls, (p<0.05). There was not differences in carcass and mortality. Costs were lower with antibiotic and higher in control treatment. Allometric growth constants in liver and jejunum were higher in all groups compared with control group (p<0.05). Intestinal pH (jejunum) was lower in the organic acid and the mixture-treated groups. The combined diest supplemented with a prebiotic and an organic acid showed synergism

COOPERATION IN LARGE NETWORKS: AN EXPERIMENTAL

We present a new design of a simple public goods experiment with a large number of players, where up to 80 people in a computer lab have the possibility to connect with others in the room to induce more cooperators to contribute to the public good and overcome the social dilemma. This experimental design explores the possibility of social networks to be used and institutional devices to create the same behavioral responses we observe with small groups (e.g. commitments, social norms, reciprocity, trust, shame, guilt) that seem to induce cooperativebehavior in the private provision of public goods. The results of our experiment suggest that the structure of the network affects not only the players´ ability to communicate, but their willingness to do so as well. Finally, we find that the local connectivity structure of the network has an important role as determinant of the willingness of the players to engage in a more costly type of collective action, namely the endogenous creation of new links to individuals previously out of reach.Social capital, social networks, collective action, cooperation, VCM,experiments, public goods provision

Do Natural Disasters Have Long-term Effects on Growth?

Large natural disasters (LNDs) are ubiquitous phenomena with potentially large impacts on the infrastructure and population of countries and on their economic activity in general. Using a panel of 113 countries and 36 years of data, I examine the relationship between different measures of natural disaster impact and long-run economic growth. The sample is partitioned in two separate ways: according to the amount and type of disasters that countries have experienced and to the size of those disasters. For each partition, I present two sets of econometric estimations. The first regressions identify short-run and longer-lasting effects of LNDs. However, these first estimations do not distinguish between temporary but persistent effects and truly permanent ones. I thus estimate a structural model that allows me to identify permanent changes. The results of the first regressions show that for some of the groups of countries the disaster impact persists beyond the 2-5 years in which reconstruction and adaptation are expected to have an effect on the economy. However, the estimates using the structural model show that only for a very small number of countries which share a history of highly devastating natural disasters the negative effects are truly permanent.Natural disasters, catastrophes, hurricanes, earthquakes, growth, panel data.