1000 resultados para Decisió, Presa de -- Models matemàtics


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We characterize the class of strategy-proof social choice functions on the domain of symmetric single-peaked preferences. This class is strictly larger than the set of generalized median voter schemes (the class of strategy-proof and tops-only social choice functions on the domain of single-peaked preferences characterized by Moulin (1980)) since, under the domain of symmetric single-peaked preferences, generalized median voter schemes can be disturbed by discontinuity points and remain strategy-proof on the smaller domain. Our result identifies the specific nature of these discontinuities which allow to design non-onto social choice functions to deal with feasibility constraints.

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This paper analyzes the problem that an incumbent faces during the legislature when deciding how to react to popular initiatives or policy proposals coming from different sources. We argue that this potential source of electoral disadvantage that the incumbent obtains after being elected can jeopardize the reelection possibilities of the incumbent. We analyze the decision of the incumbent when facing reelection and we characterize the conditions under which the advantages that the incumbent obtains can overcome the disadvantages. Finally, we use the results of this analysis to discuss some implications of the use of mechanisms of direct democracy like referenda and popular assemblies on electoral competition.

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We examine the interactions between individual behavior, sentiments and the social contract in a model of rational voting over redistribution. Agents have moral "work values". Individuals' self-esteem and social consideration of others are endogenously determined comparing behaviors to moral standards. Attitudes toward redistribution depend on self-interest and social preferences. We characterize the politico-economic equilibria in which sentiments, labor supply and redistribution are determined simultaneously. The equilibria feature different degrees of "social cohesion" and redistribution depending on pre-tax income inequality. In clustered equilibria the poor are held partly responsible for their low income since they work less than the moral standard and hence redistribution is low. The paper proposes a novel explanation for the emergence of different sentiments and social contracts across countries. The predictions appear broadly in line with well-documented differences between the United States and Europe.

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We discuss the recent emergence of "deliberative ecological economics", a field that highlights the potential of deliberation for improving environmental governance. We locate the emergence of this literature in the long concern in ecological economics over the policy implications of limited views of human action and its encounter with deliberative democracy scholarship and the model of communicative rationality as an alternative to utilitarianism. Considering criticisms over methods used and the focus of research in deliberative decision-making, we put forward a research agenda for deliberative ecological economics. Given the promising potential of deliberative processes for improving the effectiveness and legitimacy of environmental decision-making, work in this area could help advance both theory and practice in environmental governance.

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We experimentally investigate in the laboratory two prominent mechanisms that are employed in school choice programs to assign students to public schools. We study how individual behavior is influenced by preference intensities and risk aversion. Our main results show that (a) the Gale-Shapley mechanism is more robust to changes in cardinal preferences than the Boston mechanism independently of whether individuals can submit a complete or only a restricted ranking of the schools and (b) subjects with a higher degree of risk aversion are more likely to play "safer" strategies under the Gale-Shapley but not under the Boston mechanism. Both results have important implications for the efficiency and the stability of the mechanisms.

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This paper is the first to use a randomized trial in the US to analyze the short- and long-term educational and employment impacts of an afterschool program that offered disadvantaged high-school youth: mentoring, educational services, and financial rewards with the objective to improve high-school graduation and postsecondary schooling enrollment. The short-term hefty beneficial average impacts quickly faded away. Heterogeneity matters. While encouraging results are found for younger youth, and when the program is implemented in relatively small communities of 9th graders; detrimental longlived outcomes are found for males, and when case managers are partially compensated by incentive payments and students receive more regular reminders of incentives.

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Since World War II there have been about fifty episodes of large-scale mass killings of civilians and massive forced displacements. They were usually meticulously planned and independent of military goals. We provide a model where conflict onset, conflict intensity and the decision to commit mass killings are all endogenous, with two main goals: (1) to identify the key variables and situations that make mass killings more likely to occur; and (2) to distinguish conditions under which mass killings and military conflict intensity reinforce each other from situations where they are substitute modes of strategic violence. We predict that mass killings are most likely in societies with large natural resources, significant proportionality constraints for rent sharing, low productivity and low state capacity. Further, massacres are more likely in a civil than in an interstate war, as in the latter group sizes matter less for future rents. In non polarized societies there are asymmetric equilibria with only the larger group wanting to engage in massacres. In such settings the smaller group compensates for this by fighting harder in the first place. In this case we can talk of mass killings and fighting efforts to be substitutes. In contrast, in polarized societies either both or none of the groups can be ready to do mass killings in case of victory. Under the "shadow of mass killings" groups fight harder. Hence, in this case massacres and fighting are complements. We also present novel empirical results on the role of natural resources in mass killings and on what kinds of ethnic groups are most likely to be victimized in massacres and forced resettlements, using group level panel data.

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This paper surveys the literature on strategy-proofness from a historical perspective. While I discuss the connections with other works on incentives in mechanism design, the main emphasis is on social choice models. This article has been prepared for the Handbook of Social Choice and Welfare, Volume 2, Edited by K. Arrow, A. Sen and K. Suzumura

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This paper is the first to use a randomized trial in the US to analyze the short- and long- term impacts of an afterschool program that offered disadvantaged high-school youth: mentoring, educational services, and financial rewards to attend program activities, complete high-school and enroll in post-secondary education on youths' engagement in risky behaviors, such as substance abuse, criminal activity, and teenage childbearing. Outcomes were measured at three different points in time, when youths were in their late-teens, and when they were in their early- and their latetwenties. Overall the program was unsuccessful at reducing risky behaviors. Heterogeneity matters in that perverse effects are concentrated among certain subgroups, such as males, older youths, and youths from sites where youths received higher amount of stipends. We claim that this evidence is consistent with different models of youths' behavioral response to economic incentives. In addition, beneficial effects found in those sites in which QOP youths represented a large fraction of the entering class of 9th graders provides hope for these type of programs when operated in small communities and supports the hypothesis of peer effects.

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We study a symmetric information bargaining model of civil war where a third (foreign) party can affect the probabilities of winning the conflict and the size of the post conflict spoils. We show that the possible alliance with a third party makes peaceful agreements difficult to reach and might lead to new commitment problems that trigger war. Also, we argue that the foreign party is likely to induce persistent informational asymmetries which might explain long lasting civil wars. We explore both political and economic incentives for a third party to intervene. The explicit consideration of political incentives leads to two predictions that allow for identifying the influence of foreign intervention on civil war incidence. Both predictions are confirmed for the case of the U.S. as a potential intervening nation: (i) civil wars around the world are more likely under Republican governments and (ii) the probability of civil wars decreases with U.S. presidential approval rates.

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This article builds a micro founded model of the clash of cultures. The clash is defined as the parent's fear of a trait change by their child in an overlapping generations model with intergenerational transmission of cultural traits. The extent of the clash is manipulated by cultural leaders who benefit from the cultural education effort by parents. We identify three channels through which the leaders can affect the clash of cultures: (i) by providing beneficial cultural values, (ii) by claims of cultural superiority and (iii) by cultural alienation, i.e. by inducing cultural dislike towards their own group. We show that all three channels can be in the leader's interest but channels (ii) and (iii) reduce the utility of the leader's goup members. This hints to a strong conflict of interest within groups - between the population at large and the benefactors of radicalization. We further show how the use of alienation relates to the economic opportunities available to a group.

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This paper examines the impact of ethnic divisions on conflict. The analysis relies on a theoretical model of conflict (Esteban and Ray, 2010) in which equilibrium conflict is shown to be accurately described by a linear function of just three distributional indices of ethnic diversity: the Gini coefficient, the Hirschman-Herfindahl fractionalization index, and a measure of polarization. Based on a dataset constructed by James Fearon and data from Ethnologue on ethno-linguistic groups and the "linguistic distances" between them, we compute the three distribution indices. Our results show that ethnic polarization is a highly significant correlate of conflict. Fractionalization is also significant in some of the statistical exercises, but the Gini coefficient never is. In particular, inter-group distances computed from language and embodied in polarization measures turn out to be extremely important correlates of ethnic conflict.

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The problem of waste management is causing growing concern due to increasing generation rates, the emissions into soil, water and air, the social conflicts derived from the election of disposal sites and the loss of resources and energy among others. In this work, an innovative methodology is used to enable a better understanding of the waste generation and management system in Italy. Two new waste indicators are built to complement the conventional indicators used by official statistics. Then a multi-scale analysis of the Density of Waste Disposed (DWD) is carried out to highlight the territorial diversity of waste performances and test its contribution to detect plausible risky areas. Starting from Italian regions, the scale down goes on to the provincial level and, only for the region of Campania, the municipal one. First, the analysis shows that the DWD is able to complement the information provided by the conventional waste indicators. Second, the analysis shows the limitations of using a unique institutional solution to waste management problems. In this sense the multi-scale analysis provides with a more realistic picture of Italian waste system than using a single scale.

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Aquest projecte proposa materials didàctics per a un nou plantejament de les assignatures de Matemàtiques dels primers cursos de Ciències Empresarials i d'Enginyeria Tècnica, més acord amb el procés de convergència europea, basat en la realització de projectes que anomenem “Tallers de Modelització Matemàtica” (TMM) en els quals: (1) Els alumnes parteixen de situacions i problemes reals per als quals han de construir per sí mateixos els models matemàtics més adients i, a partir de la manipulació adequada d’aquests models, poden obtenir la informació necessària per donar-los resposta. (2) El treball de construcció, experimentació i avaluació dels models es realitza amb el suport de la calculadora simbòlica Wiris i del full de càlcul Excel com a instruments “normalitzats” del treball matemàtic d’estudiants i professors. (3) S’adapten els programes de les assignatures de matemàtiques de primer curs per tal de poder-les associar a un petit nombre de Tallers que parteixen de situacions adaptades a cada titulació. L’assignatura de Matemàtiques per a les Ciències Empresarials s’articula entorn de dos tallers independents: “Matrius de transició” pel que fa a l’àlgebra lineal i “Previsió de vendes” per a la modelització funcional en una variable. L’assignatura de Matemàtiques per a l’Enginyeria s’articula entorn d’un únic taller, “Models de poblacions”, que abasta la majoria de continguts del curs: successions i models funcionals en una variable, àlgebra lineal i equacions diferencials. Un conjunt d’exercicis interactius basats en la calculadora simbòlica WIRIS (Wiris-player) serveix de suport per al treball tècnic imprescindible per al desenvolupament de les dues assignatures. L’experimentació d’aquests tallers durant 2 cursos consecutius (2006/07 i 2007/08) en dues universitats catalanes (URL i UAB) ha posat en evidència tant els innegables avantatges del nou dispositiu docent per a l’aprenentatge dels estudiants, així com les restriccions institucionals que actualment dificulten la seva gestió i difusió.

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Este trabajo de investigación se centra en la problemática hídrica y, concretamente, en el enfoque con el que, actualmente, se describen y se tratan estos problemas. Así, se analiza el modelo estructuralista hidráulico como una de estas fuentes de interpretación y proposición. Pero, también, se estudia cómo ha contribuido la labor científica que realizan en este contexto los expertos sobrre aguas -principalmente, ingenieros y técnicos- a establecer el "framing" predominante. Con la preocupación de estar tratando con un recurso vital que ante una distribución y gestión hídricas deficientes o inapropiadas genera problemas prácticos de urgente resolución, se empieza a cuestionar, como hacen las nuevas concepciones como la gestión integrada de cuencas hidrográficas o la Nueva Cultura del Agua, el modo actual de enmarcar el problema. En este sentido, se adopta como objetivo tratar de reverter la dinámica de crecimiento de la demanda y encontrar fórmulas no centralizadas de gestión, que no requieran un conocimiento completo del sistema hidrológico y de gestión, que no detenten visiones fragmentadas de la situación hídrica y que no mantengan un "framing" estático y determinista. Y, para ello, se toma como inicio, lo que sucede en los conflictos en torno al agua. Así, se considera la tensión que existe entre "nuevos" y "viejos" paradigmas no sólo una discusión académico-teórica, sino, también una cuestión de gobernabilidad hídrica. De este modo, se presenta como una oportunidad para el cambio tanto la situación compleja e incierta que caracteriza y envuelve la gestión del agua como la diversidad de "miradas" al problema (y de soluciones) que existen en la contingencia social. Además, se contemplan, como sugerencias de innovación conceptual y procedural, los mecanismos de interacción, comunicación y presión que surgen en estos contextos. Se aborda el caso del canal de riego del Segarra-Garrigues en Lleida, precisamente, para indagar en todos estos aspectos, como un ejemplo de este encuentro entre nuevas realidades y anacrónicas incercias y de la inquietud de algunos actores por redefinir el "framing" hegemónico. Para ello, se da especial importancia a los procesos de toma de decisiones y de generación del conocimiento, prestando atención a cómo condicionan, en los problemas y en la búsqueda de soluciones, la filosofía e ideología científica y política empleadas en el marco del agua. De este análisis se desprenden algunas opciones para experimental en etapas venideras de la investigación. En este documento, entonces, se discute sobre qué otros modes de investigar-decidir-actuar podrían darse, pero también, se describe qué se ha hecho, hasta el momento, al respecto. En este sentido, aparecen cuestiones como la redeficinión del rol del experto-investigador, la práctica participativa en la generación del conocimiento, la sinergia entre las motivaciones científico-teóricas con las preocupaciones locales y la integración entre el estudio y los procesos de (auto)organizativos que se dan en el conflicto. Y, en definitiva, se hacen patentes muchos de los retos que enfrentan hoy en día la gestión y placificación hidrológicas.