risk sharing and contagion in networks we investigate the socially optimal design of financial networks that allows to tackle the trade off between risk sharing and contagion we identify conditions on the shock distribution under which full integration or maximal segmentation is optimal we also show that under different conditions the optimal network displays different levels of strength of linkages to other firms or intermediate degrees of segmentation in the latter case the individual and social incentives to establish linkages are not necessarily aligned when firms face heterogeneous distributions of risks they should optimally form linkages only with firms facing risks of the same kind

hybrid r d we develop a model of r d collaboration in which individual firms carry out in house research on core activities and undertake bilateral joint projects on non core activities with other firms we develop conditions on the profit functions of the firm under which r d investments in different projects of a firm are complementary we show that this condition is met by standard price and quantity setting oligopoly models we then study the relation between the number of joint projects and investments and profits in this context we identify a second aspect of complementarity equilibrium investments in in house as well as in each joint project are increasing in the number of projects however we find that an increase in number of joint projects of all firms lowers collective profits suggesting the presence of excessive incentives for conducting research

learning about a new technology pineapple in ghana this paper investigates the role of social learning in the diffusion of a new agri cultural technology in ghana we use unique data on farmers communication patterns to define each individual s information neighborhood conditional on many potentially confounding variables we find evidence that farmers adjust their inputs to align with those of their information neighbors who were surpris ingly successful in previous periods the relationship of these input adjustments to experience further indicates the presence of social learning in addition applying the same method to input choices for another crop of known technol ogy correctly indicates an absence of social learning effects jel d83 013 033 q16

information gathering through alliances abstract the effect of a firm s uncertainty regarding technological development on the formation of alliances is examined and it is shown that this uncertainty is positively related to the number of alliances however higher uncertainty also makes the firm less likely to ally with others if the collected information is redundant the higher the similarity between the technological regimes of potential alliance partners the lower the incentive to ally also direct ties are preferred to indirect ones if uncertainty is high since direct ties yield more accurate information than indirect ties

the effect of entry on r d networks we investigate the effect of potential entry on the formation and stability of r d networks considering farsighted firms we show that the presence of a potential entrant often alters the incentives of incumbent firms to establish an r d link in particular incumbent firms may choose to form an otherwise undesirable r d collaboration in order to deter the entry of a new firm moreover an incumbent firm may refrain from establishing an otherwise desirable r d collaboration expecting to form a more profitable r d link with the entrant finally potential entry may lead an inefficient incumbent to exit the market we also perform a welfare analysisand show that market and societal incentives are often misaligned

labour im mobility and monopsonistic exploitation of workers in the urban informal sector lessons from a field study it is well recognised in labour economics that employers in monopsonistic competition have market power to set wages below the productivity of workers if workers are immobile which causes monopsonistic exploitation of workers monopsonistic exploitation is propelled by employers expectations about the degree of im mobility of workers and therefore by ex post mobility of workers it hence begs a question of what determines the relative im mobility of informal workers which has significant implications for monopsonistic exploitation and working poverty in the urban informal sector from our field study of urban and peri urban labour markets in bangladesh by modifying the method of stochastic frontier analysis we explain the behavioural foundation to the relative im mobility of informal workers we thereby unravel the effects of individual and household characteristics sociological institutional factors and household ties including worker s kinship on the relative immobility of a worker that can in turn explain monopsonistic exploitation and working poverty widely prevalent in the urban informal sector of south asia

community membership aspirations the link between inequality and redistribution revisited the issue at stake is to explain why redistributive policies may vary so greatly for a given distributional skewness to this end we abandon the stylized median voter and study how distributional tensions can act in many different ways depending on social affinity between the different economic classes and their prospect of upward or downward mobility in particular we consider that socioeconomic group membership through its implied social interactions and peer effects is an important determinant of an individual s outcome hence agents while voting on a social contract must take into account the consequences of their choice over their ex post belonging to a particular community this allows us to shed light on how the endogenous sorting of the population into clusters may interact with the balance of political power leading to a non monotonic relationship through the pattern of community formation in the economy between inequality and the pressure for redistributive policies

the impact of legislation on divorce a hazard function approach the paper examines the impact of the introduction of no fault divorce legislation in australia the approach used is rather novel a hazard model of the divorce rate is estimated with the role of legislation captured via a time varying covariate the paper concludes that contrary to us empirical evidence no fault divorce legislation appears to have had a positive impact upon the divorce rate in australia

endogenous formation of cooperation structures abstract i consider a cooperation formation game in which players choose independently with whom they wish to cooperate in a given coalitional game and players payoffs follow a solution imposed on the coalitional game i study the resulting equilibrium cooperation structure and how cooperation evolves under best response and fictitious play learning processes journal of economic literatureclassification numbers c71 c72

attack defence and contagion in networks sanjeev goyal acknowledges support from a keynes fellowship cambridge inet institute and european research area complexity net resilience and interaction of networks in ecology and economics adrien vigier acknowledges support from a gates cambridge fellowship as well as a core fellowship from universite catholique de louvain

intra firm bargaining under non binding contracts we present a new methodology for studying the problem of intra firm bargaining based on the notion that contracts cannot commit the firm and its agents to wages and employment we develop and analyse a general non cooperative multilateral bargaining framework between the firm and its employees and consider outcomes which are immune to renegotiations by any party equilibrium firm profits are characterizable as both a weighted average of a neo classical non bargaining firm s profits and a generalization of shapley value for a corresponding cooperative game furthermore the resulting payoffs induce economically significant distortions in the firm s input and organizational design decisions

the economics of hubs the case of monopoly in this paper we study the optimization problem of an unregulated air carrier which is given the exclusive right to satisfy demand for air travel between any pair of cities it chooses a network of connections and a set of prices to maximize profits thus both network design and prices are endogenous we characterize the solution to this optimization problem when demands and costs are symmetric our main result is that if there are economies of density in the number of individuals travelling between two directly connected cities the optimal network is either a hub of size n 1 or one in which every pair of cities is connected directly

networks of collaboration in oligopoly abstract in an oligopoly prior to competing in the market firms have an opportunity to form pair wise collaborative links with other firms these pair wise links involve a commitment of resources and lead to lower costs of production of the collaborating firms we study the incentives of firms to form links and the architecture of the resulting collaboration network we find that incentives to form links are intimately related to the nature of market competition our analysis also suggests that collaborations are used by firms to generate competitive advantage and that strategically stable networks are often asymmetric with some firms having many links while others have few links or are isolated specifically we show that networks with the dominant group architecture stars and inter linked stars are stable we also present some results on the architecture of socially efficient networks

the ecological economic and social importance of the oceans abstract the oceans have long been recognized as one of humanity s most important natural resources their vastness has made them appear to be limitless sources of food transportation recreation and awe the difficulty of fencing and policing them has left them largely as open access resources to be exploited by anyone with the means however in recent times we have begun to reach the limits of the oceans and must now begin to utilize and govern them in a more sustainable way this paper summarizes emerging information on the interrelated ecological economic and social importance of the oceans and on developing institutions for their sustainable governance in addition to their traditional importance as sources of primary and secondary production and biodiversiy the importance of the oceans in global material and energy cycles is now beginning to be better appreciated integrated models of the global ocean atmosphere terrestrial biosphere system reveal the critical role of the oceans in atmospheric gas and climate regulation and for water nutrient and waste cycling recent estimates of the economic value of the marketed and non marketed ecosystem services of the oceans indicate a huge contribution to human welfare from the functions mentioned above plus raw materials recreational and cultural services the oceans have been estimated to contribute a total of 21 trillion us year to human welfare compared with a global gnp of 25 trillion us with 60 of this from coastal and shelf systems and the other 40 from the open ocean and with the oceans contributing 60 of the total economic value of the biosphere costanza et al 1997 the value of the world s ecosystem services and natural capital nature 387 253 260 the social importance of the oceans for global transportation and as a unifying element in the cultures of many coastal countries cannot be overestimated however the cultural traditions of open access must be replaced with more appropriate property rights regimes and governance structures some alternative sustainable governance ideas are briefly discussed emphasizing the need for an expanded deliberative process to develop a shared vision of a sustainable use of oceans

does whom you know matter unraveling the influence of peers network attributes on academic performance this paper examines how students network size distance prestige and connections to influential individuals impact academic performance larger and closer networks facilitate information exchange but may also increase distractions that decrease productivity we resolve this ambiguity using administrative data from a business school that features random assignment of students to multiple overlapping sets of peers allowing us to calculate degree closeness eigenvector and katz bonacich centrality for each node we find that increasing closeness centrality within the network negatively affects student performance measured by grade point average suggesting that synergy reduction and information processing costs outweigh benefits from greater information access jel i23 l14 l23

the design of fishing right systems the nsw experience abstract in 1994 the australian state of new south wales nsw passed legislation to introduce a fishery share system in some ways it is similar to the itq or individual transferable quota fishery management systems found in new zealand iceland australia canada and other countries the focus of the system however is on fisheries rather than species in most of these fisheries a combination of input and output controls are used special design features include allotment of shares in the fishery rather than in quotas and a structure that forces adaptive resource management the system is designed to maximise the probability that fishery use will remain both sustainable and consistent with social objectives as they change through time the system s conceptual framework is of relevance to other fisheries and also many other industries that use natural resources consistent with periodically revised management plans rights to harvest specific amounts of fish or to use certain classes of boats and gear are issued in proportion to the number of shares held in each fishery fishery being flexibly defined by region and habitat with or without further specification by gear type species group or single species the management plan might for example specify a relationship between number of shares and size of boat or net any quotas are allocated in proportion to the number of shares held subject to compliance with periodically reviewed share conditions rights are perpetual and give each fisher a direct financial interest in the future of the fishery shares are mortgageable and fully transferable driven by the management plan structural adjustment is delegated to the market and individual fishers a dual property right structure is used to minimise transfer costs encourage self enforcement and compliance

bargaining in a network of buyers and sellers abstract we analyze bargaining between buyers and sellers who are connected by an exogenously given network players can make repeated alternating public offers that may be accepted by any of the responders linked to each specific proposer our purpose is to find the conditions of the network which drive the price distribution in equilibrium this paper uses graph theory tools to provide necessary and sufficient conditions regarding the architecture of networks for the subgame perfect equilibrium of the bargaining game to coincide with the walrasian outcome

allocating value among farsighted players in network formation we study the stability of networks when players are farsighted and allocations are determined endogenously the set of strongly efficient networks is the unique von neumann morgenstern farsightedly stable set with bargaining if the value function is anonymous component additive and top convex and the allocation rule is anonymous and component efficient moreover the componentwise egalitarian allocation rule emerges endogenously

preferential versus multilateral trade liberalization and the role of political economy abstract in this paper we analyze the effect of the freedom to pursue preferential trade liberalization permitted by article xxiv of the gatt on country s incentives to participate in multilateral negotiations and on feasibility of global free trade we present a model in which countries choose whether to participate in preferential or multilateral trade agreements under political pressures from domestic special interest groups we show that heterogeneity in political preferences across countries plays an important role in determining the relative merits of preferential and multilateral approaches to trade liberalization on one hand the opportunity to liberalize preferentially may be necessary to induce countries with strong political motivations to participate in multilateral free trade negotiations on the other hand when countries share similar political preferences multilateral free trade that would have been politically supported otherwise becomes unattainable if countries can pursue preferential liberalization

a one stage model of link formation and payoff division abstract in this paper we introduce a strategic form model in which cooperation structures and divisions of the payoffs are determined simultaneously we analyze the cooperation structures and payoff divisions that result according to nash equilibria strong nash equilibria and coalition proof nash equilibria we find that no cycle will be formed if a player claims a positive amount for the formation of one of its links and that a player does not necessarily profit from a central position in a cooperation structure journal of economic literature classification numbers c71 c72

cooperation through imitation and exclusion in networks we develop a simple model to study the coevolution of interaction structures and action choices in prisoners dilemma games agents are boundedly rational and choose both actions and interaction partners via payoff biased imitation the dynamics of imitation and exclusion yields polymorphic outcomes under a wide range of parameters whenever agents hold some information beyond their interaction neighbors defectors and cooperators always coexist in disconnected components otherwise polymorphic networks can emerge with a center of cooperators and a periphery of defectors any stochastically stable state has at most two disconnected components simulations confirm our analytical results and show that the share of cooperators increases with the speed at which the network evolves increases with the radius of interaction and decreases with the radius of information

bilateral bargaining in networks abstract each connected pair of nodes in a network can jointly produce one unit of surplus a maximum number of linked nodes is selected in every period to bargain bilaterally over the division of the surplus according to the protocol proposed by rubinstein and wollinsky equilibrium in a market with sequential bargaining econometrica 53 1985 1133 1150 all pairs which reach an agreement obtain the discounted payoffs and are removed from the network this bargaining game has a unique subgame perfect equilibrium that induces the dulmage mendelsohn decomposition partition of the bipartite network of the set of nodes in this network

marriage and divorce reply in the popular press and among policymakers the effect of no fault divorce laws on divorce rates remains an issue see e g new york times 23 july 1991 in my 1986 article in this review i show that the adoption of one form of no fault divorceunilateral divorce does not lead to a significant increase in divorce rates the theoretical model that is consistent with this empirical evidence would imply that the new law does not decrease the costs of divorce it merely redefines which party has the right to terminate the marriage

peer effects in endogenous networks abstract this paper presents a model of strategic network formation with local complementarities in effort levels and positive local externalities results are obtained for a general class of payoff functions which subsumes the linear quadratic specification frequently used in theoretical and applied work we assume homogeneous agents and characterize equilibria for two sided and one sided link formation pairwise nash equilibrium networks are nested split graphs which are a strict subset of core periphery networks we highlight the relevance of the convexity of the value function for obtaining these structures more central agents are shown to exert more effort and obtain higher gross payoffs in equilibrium however net of linking cost central agents may obtain strictly lower net payoffs the curvature of the value function is also important for efficiency considerations these findings are relevant for many social and economic phenomena such as educational attainment criminal activity labor market participation and r d expenditures of firms

forward looking behavior in hawk dove games in endogenous networks experimental evidence abstract we conduct an experiment in continuous time every subject can change her links to others and her action in a hawk dove game which she plays bilaterally with each of her linked partners at any time we hypothesize that norms exist regarding who establishes and thus pays for links and that players take these norms into account when deciding on their strategy for such limitedly forward looking players who consider others linking reactions we introduce a strategy adaptation rule anticipatory better reply rule abr and a related stability criterion reaction anticipatingly stable ras our data support our assumption on linking reactions subjects seem to take these reactions into account when deciding to switch from hawk to dove abr behavior however better reply behavior is prevalent when short term profits allure ras configurations occur more often than nash equilibria of the base game however with respect to stability they perform similar

price formation on the marseille fish market evidence from a network analysis abstract the empirical analysis of fish markets always reveals strong price dispersion for homogeneous or very similar goods the problem is how to explain this price dispersion on a market where there is no evident arbitrage explanations proposed by different authors include differences in organization the characteristics of the good and the influences of social interactions between buyers and sellers in line with the last of these three approaches we consider the fish market of marseille as a seller seller network we start by examining the influence of market interactions through a static and then a dynamic econometric model we then analyze the role of the seller s position in the network we bring to light a surprising paradox in that the sellers who share the most buyers with competitors i e the most central sellers charge the highest prices

a theory of buyer seller networks this paper introduces a new model of exchange networks rather than markets of buyers and sellers it begins with the empirically motivated premise that a buyer and seller must have a relationship a link to exchange goods networks buyers sellers and the pattern of links connecting them are common exchange environments this paper develops a methodology to study network structures and explains why agents may form networks in a model that captures characteristics of a variety of industries the paper shows that buyers and sellers acting strategically in their own self interests can form the network structures that maximize overall welfare

job information networks neighborhood effects and inequality this paper explores the theoretical and empirical literature to examine the use by different social groups of informal sources of information provided by friends relatives and acquaintances during job search and its consequences for the job market it also addresses the role of network structure and size the resource endowments of contacts and nature of the links between contacts to explain differences in the effects of job information networks in doing so the paper also turns to the sociology literature on job information networks and provides an economic perspective on such sociological concepts as strong versus weak ties inbreeding distance from structural holes etc the paper distinguishes between models of exogenous job information networks that is where individuals obtain job related information through a given social structure and endogenous job information networks which are social networks that result from individuals uncoordinated actions the paper pays special attention to such issues as physical and social proximity and sharing of information and discusses them in the context of the recent social interactions and neighborhood effects literature finally the paper outlines a model that integrates job information networks where interactions occur in business cycle frequencies with the dynamics of human capital formation which include the joint effects of parental community and neighborhood human capital and are set in life cycle frequencies for the purpose of organizing suggestions for future research and examining earned income inequality

from simplistic to complex systems in economics the applicability of complex systems theory in economics is evaluated and compared with standard approaches to economic theorising based upon constrained optimisation a complex system is defined in the economic context and differentiated from complex systems in physio chemical and biological settings it is explained why it is necessary to approach economic analysis from a network rather than a production and utility function perspective when we are dealing with complex systems it is argued that much of heterodox thought particularly in neo schumpeterian and neo austrian evolutionary economics can be placed within a complex systems perspective upon the economy the challenge is to replace prevailing simplistic theories based in constrained optimisation with simple theories derived from network representations in which value is created through the establishment of new connections between elements

worker substitutability and patterns of unionisation a strategic three party bargaining model is developed in which one distinguished party the firm has to reac h agreements with the other two each of which is a group of workers in the prebargaining stage the two worker groups decide whether to organize jointly or separately the main observation relates the equi librium pattern of unionization to the substitutability in production between the two groups the outcome is joint or separate unions acco rding to whether the two groups are substitute or complementary facto rs of production the analysis also considers possibilities for firm s strategic intervention in the unionization process copyright 1988 by royal economic society

from exogenous to endogenous economic networks internet applications economic agents behaviour is affected by their position in a network either exogenous or endogenous in which they interact with a sub set of neighbours only the network s links which may be generated by vertical and or horizontal relations or by more complex morphologies may explain the transition between dynamic equilibria and the instability of economic aggregates moreover networks shape strategic interaction among agents by determining their strategies the problem of access and interconnection particularly relevant in the internet is perhaps the best example a two way feedback between strategies and network structures arises instead when links are endogenous those features are clearly shown in the mechanism underlying the formation of peering links an dr d networks

core and periphery in networks abstract we study a model of network formation where the benefits from connections exhibit decreasing returns and decay with network distance we show that the unique equilibrium network is a periphery sponsored star where one player the center maintains no links and earns a high payoff while all other players maintain a single link to the center and earn lower payoffs both the star architecture and payoff inequality are preserved in an extension of the model where agents can make transfers and bargain over the formation of links under the condition that the surplus of connections increases in the size of agents neighborhoods our model thus generates two common features of social and economic networks 1 a core periphery structure 2 positive correlation between network centrality and payoffs

strategic communication networks in this paper we consider situations in which individuals want to choose an action close to others actions as well as close to a payoff relevant state of nature with the ideal proximity to the common state varying across the agents before this coordination game with heterogeneous preferences is played a cheap talk communication stage is offered to players who decide to whom they reveal the private information they hold about the state the strategic information transmission taking place in the communication stage is characterized by a strategic communication network we provide a direct link between players preferences and the strategic communication network emerging at equilibrium depending on the strength of the coordination motive and the prior information structure equilibrium strategic communication networks are characterized in a very tractable way and compared in term of efficiency in general a maximal strategic communication network may not exist and communication networks cannot be ordered in the sense of pareto however expected social welfare always increases when the communication network expands strategic information transmission can be improved when group or public communication is allowed and or when information is certifiable

risk sharing across communities this paper studies cross community risk sharing there is now a large body of theoretical and empirical work on informal insurance where people mitigate risk by sharing income a consistent empirical finding is that risk sharing is not complete within villages often the observed sets of individuals 2 one reason researchers suspect is that risk sharing does not take place at the village level but between individuals and families 3 we build a theoretical model where risksharing takes place between pairs of agents there are idiosyncratic shocks to individual income and community level shocks we consider how the opportunity for cross community links affects the shape and efficiency of risk sharing arrangements we find that when links across villages form there can be less risk sharing within a village welfare is higher for those directly or indirectly connected across villages but lower for those with no path connecting them to the other village overall welfare can be higher thus empirical findings that insurance within a village is not complete is not necessarily evidence of an inefficient pattern of risk sharing relations rather the finding is consistent with risk sharing patterns that involve cross community relations and such patterns may yield higher aggregate welfare despite incomplete insurance within a village this paper makes two contributions first it demonstrates the importance of a network analysis by examining pairwise incentives to form relations and the resulting pattern we can see new risk sharing outcomes second with this network model we show how informal risk sharing across communities has both aggregate and distributional effects to study network outcomes we posit a simple two stage model first we provide a benchmark model for risk sharing for a given network then working backwards we consider incentives to form risk sharing links 4 to illustrate consider a rural population and ask how people might link

principles of network development and evolution an experimental study this paper reports on an experimental investigation of the evolution of networks and the individual decision making processes that guide it inasmuch as there is no history of experimental work on network formation part of the paper is devoted to the formulation of problems that can be examined experimentally the results are that networks composed of decentralized decision makers are capable of overcoming complex coordination and learning problems and converge to stationary when it does not occur significant and persistent inefficiencies can result the models of equilibration based on the principle of nash equilibrium are more reliable than models based on the alternative principles of efficiency seeking or focalness of the network configuration however individual decision making within networks is not in accordance with the simple decision rules of nash best response instead we observed complicated strategies that appear to trade short term profits in order to signal to and teach other agents the strategies required for long term profit maximization

asset pricing in large information networks we study asset pricing in economies with large information networks we focus on networks that are sparse and have power law degree distributions in line with empirical studies of large scale social networks our theoretical framework yields a rich set of novel asset pricing implications we derive closed form expressions for price volatility profitability and trading volume as functions of the network topology we also study agent welfare and show that the network that optimizes total welfare is typically a uniform one with an intermediate degree of connectedness

equilibria in networks we study a model in which two carriers choose networks to connect cities and compete for customers we show that if carriers compete aggressively e g bertrand like behavior one carrier operating a single hub spoke network is an equilibrium outcome competing hub spoke networks are not an equilibrium outcome although duopoly equilibria in nonhub networks can exist if carriers do not compete aggressively an equilibrium with competing hub spoke networks exists as long as the number of cities is not too small we provide conditions under which all equilibria consist of hub spoke networks

coalition formation as a dynamic process abstract we study coalition formation as an ongoing dynamic process with payoffs generated as coalitions form disintegrate or regroup a process of coalition formation pcf is an equilibrium if a coalitional move to some other state can be justified by the expectation of higher future value compared to inaction this future value in turn is endogenous it depends on coalitional movements at each node we study existence of equilibrium pcfs we connect deterministic equilibrium pcfs with unique absorbing state to the core and equilibrium pcfs with multiple absorbing states to the largest consistent set in addition we study cyclical as well as stochastic equilibrium pcfs

strong and weak links many of the interesting issues in the economics of networks information transmission individual incentives with local externalities investments in connections and the structure of complex networks have to do with the quality of links between individuals entities however most of the research to date has assumed a one zero formulation of connections i argue that it is possible to write down tractable models of quality of links and that analyzing such models yields fresh insights into these issues jel c72 d85 z13

ecological economics and sustainable governance of the oceans abstract this paper is an introduction and synthesis of the papers that appear in this special issue devoted to the sustainable governance of the oceans the special issue contains papers on various aspects of the problem including the ecological and economic importance of the oceans the problems facing the oceans from an ecological economics perspective the links between science and policy the rationale for sustainable ocean governance and examples of sustainable institutions and governance structures we developed the lisbon principles of sustainable governance responsibility scale matching precaution adaptive management full cost allocation and participation as a core set of guidelines for sustainable ocean governance we then describe the major problems facing the oceans in terms of how the principles are violated and evaluate some suggested institutions in terms of how the principles are incorporated

coalition theory and its applications a survey we survey some of the major advances in coalition theory in recent years we then look at the recent applications of the theory in the area of political economy and touch upon some important theoretical and applied open questions in the field

bargaining in stationary networks we study an infinite horizon game in which pairs of players con nected in a network are randomly matched to bargain players who reach agreement are replaced by new players at the same positions in the network we show that all equilibria are payoff equivalent the payoffs and the set of agreement links converge as players become patient several new concepts mutually estranged sets partners and shortage ratios provide insights into the relative strengths of the positions in the network we develop a procedure to deter mine the limit equilibrium payoffs for all players characterizations of equitable and nondiscriminatory networks are also obtained jel c78 d85 competitive equilibrium theory assumes large and anonymous markets in which every buyer can trade with every seller underlying these assumptions are standard goods and services that may be traded at low transaction costs by agents who are not in specific relationships with one another however in many markets goods and services are heterogeneous e g cars apartments or need to be tailored to particular needs e g manufacturing inputs technical support furthermore trad ing opportunities may depend on transportation costs social relationships infor mation advertising trust technological compatibility joint business opportunities free trade agreements etc in such cases it is natural to model the market using a network where only pairs of connected agents may engage in exchange new theories are needed to explore the influence of the network structure on market outcomes many questions arise how does an agent s position in the net work determine his bargaining power and the local prices he faces who trades with whom and on what terms when are prices uniform in the network one possible conjecture is that an agent s bargaining power is determined by his relative number of connections in the network however this simple theory is implausible consider the network of four sellers located at the top nodes and nine buyers located at the bottom nodes depicted in figure 1 assume that each seller supplies one unit of a homogeneous indivisible good each buyer demands one unit of the good and all buyers have identical values for the good the buyer located in the middle has the largest number of links in the network as he is connected to each

imperfect monitoring in communication networks individuals in many social networks imperfectly monitor other individuals network relationships this paper shows that in a model of a communication network imperfect monitoring leads to the existence of many inefficient equilibria reasonable restrictions on actions or on beliefs about others actions can however eliminate many of these inefficient equilibria even with imperfect monitoring star networks known to be efficient in many settings are shown to have desirable monitoring characteristics more generally this paper provides a formal framework in which to study incorrect perceptions as an equilibrium phenomenon in social networks

endogenous job contact networks we use the uk quarterly labour force survey to document the presence of two phenomena first a positive correlation between unemployment rate and the proportion of job seekers who use social networks to nd jobs network use second a non monotone relation between unemployment rate and the proportion of recently employed workers who found their job through friends or relatives network productivity this second relation is positive for low levels of unemployment rate while it becomes negative for high levels of unemployment rate existing models of social networks and labor market generally assume that social networks are exogenous this assumption implies a negative correlation between unemployment rate and network productivity we develop a model where social networks are used to collect job oers but workers decide strategically how much to invest in their network we show that equilibrium job contact networks are dense and more productive in transmitting information when labor market turnover is moderate while they are less productive and segmented into clusters for either high or low turnover the equilibrium response of job contact networks to changes in labor market conditions is sucient to generate

local network externalities and market segmentation this paper models interaction between groups of agents by means of a graph where each node represents a group of agents and an arc represents bilateral interaction it departs from the standard katz shapiro framework by assuming that network benefits are restricted only amongst groups of linked agents it shows that even if rival firms engage in bertrand competition this form of network externalities permits strong market segmentation in which firms divide up the market and earn positive profits the analysis also shows that some graphs or network structures do not permit such segmentation while for others there are easy to interpret conditions under which market segmentation obtains in equilibrium c 2009 elsevier b v all rights reserved

bayesian learning in social networks we study the perfect bayesian equilibrium of a sequential learning model over a general social network each individual receives a signal about the underlying state of the world observes the past actions of a stochastically generated neighbourhood of individuals and chooses one of two possible actions the stochastic process generating the neighbourhoods defines the network topology we characterize pure strategy equilibria for arbitrary stochastic and deterministic social networks and characterize the conditions under which there will be asymptotic learning convergence in probability to the right action as the social network becomes large we show that when private beliefs are unbounded meaning that the implied likelihood ratios are unbounded there will be asymptotic learning as long as there is some minimal amount of expansion in observations we also characterize conditions under which there will be asymptotic learning when private beliefs are bounded

challenges for economic policy in sustainable management of marine natural resources the sustainable management of marine natural resources presents particular challenges to the managers of those resources while such management has typically been based on biological considerations it is argued that this has resulted in overexploitation and destruction of important marine assets in industries such as fishing and tourism consequently it is concluded that other approaches are needed with the use of economic concepts and management tools particularly relevant at the same time the human welfare outcomes of the application of various policy instruments must be carefully considered while biological information is critical to the formulation and implementation of successful management regimes it is concluded that the application of economic instruments will become more attractive to resource managers with these instruments underpinned by consideration of property rights and an appropriate allocation of economic rents a greater focus on these economic matters will take resource managers further in the direction of sustainable management of increasingly scarce marine resources the conclusions in the paper are supported by various case studies from fisheries and tourism 2001 elsevier science b v all rights reserved

axiomatization of the shapley value on minimum cost spanning tree games abstract this paper axiomatizes the shapley value on minimum cost spanning tree games by using axioms which are different from those used in network games journal of economic literature classification numbers c71 a14

marriage and divorce informational constraints and private contracting the relationship between divorce rates in the united states and laws regulating divorce are analyzed using data from a special current population survey undertaken in 1979 with particular reference to the adoption by many states of no fault divorce laws the author utilizes a contract theoretic framework to examine the impact of both legal and informational constraints on several aspects of the marriage relationship 1 the probability of divorce 2 compensation at divorce i e the terms of the divorce settlement 3 the probability of entering marriage and 4 incentives for investment in marriage specific capital two different models are developed the first assumes that ex post information about the value of each spouses opportunites at divorce is symmetric and that since divorce would only occur if the joint benefits outweigh the joint costs the law has no effect on the divorce rate the second model asserts that the existence of asymmetric information results in a fixed wage marriage contract and that divorce would be higher in states that allow unilateral divorce the evidence supports the first of these hypotheses excerpt

the evolution of preferences why sovereign preferences may not lead to sustainable policies and what to do about it abstract the conventional economic paradigm assumes that tastes and preferences are exogenous to the economic system and that the economic problem consists of optimally satisfying those preferences tastes and preferences usually do not change rapidly and in the short term this assumption makes sense sustainability is an inherently long term problem and in the long run it does not make sense to assume tastes and preferences are fixed and given if preferences are expected to change over time and under the influence of education advertising changing cultural assumptions etc the old assumption of consumer sovereignty is not adequate different criteria of optimality are needed how preferences change how they relate to the goal of sustainability and how they can or should be actively influenced to satisfy the new criteria needs to be determined ecological economics has emphasized the three rank ordered goals of ecological sustainability fair distribution and allocative efficiency this paper examines how preferences evolve and change over time and the implications of this for developing policies that meet these three goals in democratic societies

the socially stable core in structured transferable utility games we consider socially structured transferable utility games for every coalition the relative strength of a player is measured by a power function the socially stable core consists of the socially and economically stable payoff vectors it is non empty if the game itself is socially stable the socially stable core consists of a finite number of faces of the core generically it consists of a finite number of payoff vectors convex tu games have a non empty socially stable core irrespective of the underlying social structure when the game is permutationally convex the socially stable core is shown to be non empty if the power vectors are permutationally consistent and is shown to contain a unique element if the power vectors are permutationally compatible we demonstrate the usefulness of the concept of the socially stable core by applying it to structured hierarchy games sequencing games and the distribution of water

a strategic model of social and economic networks we study the stability and efficiency of social and economic networks when self interested individuals can form or sever links first for two stylized models we characterize the stable and efficient networks there does not always exist a stable network that is efficient next we show that this tension persists generally to assure that there exists a stable network that is efficient one is forced to allocate resources to nodes that are not responsible for any of the production we characterize one such allocation rule the equal split rule and another rule that arises naturally from bargaining of the players

delegated monitoring versus arm s length contracting abstract this paper analyzes the optimal organization of input suppliers in a procurement context we discuss when a top firm chooses to induce information sharing and active coordination between its suppliers consolidation rather than having them contract at arm s length delegation in designing the organization the firm anticipates that different supplier networks have different costs of inducing information revelation from suppliers when the cost of information sharing varies the optimal organization exhibits various discrete degrees of consolidation there is excessive arm s length contracting compared to the case where the top firm controls this organizational choice itself the paper offers also a methodology to study in a unified framework various organizational forms separately analyzed in the literature

modeling bilateral electricity markets a complex network approach in electricity markets a pool trading model with a power exchange pool is a typical market organization that attracts much more attention than a bilateral trading model to date quite a few papers have focused on bilateral trading models particularly those under network constraints this trend is due to the model s complexity in terms of the various trading patterns reflecting the self interested behavior of the market participants striving to find potentially profitable transactions in this paper we propose a new approach based on complex networks suitable for assessing different aspects of bilateral market this work strives to analyze the bilateral trading patterns in the electricity markets where physical network constraints need to be considered for the feasible and secure operation of the power systems the goal of the work is to find the stable network structures that can be used to anticipate possible bilateral transactions in the real market place and to provide a novel and applicable approach to studying the bilateral model in electricity markets the proposed approach has been tested on several test systems in which the transmission network structure of the market that accommodates the transactions is considered the proposed model is illustrated with examples using a four bus test system the ieee 30 bus and the ieee 118 bus test systems

subscription mechanisms for network formation we analyze a model of network formation where the costs of forming links are publicly known but an individual s benefits are not known to the social planner the objective is to design a mechanism which not only ensures that an efficient network always forms in equilibrium but also ensures that the resulting net payoffs to the agents are equitable we propose two mechanisms towards this end in the first agents announce sequentially the set of players with whom they wish to form links and a cost contribution we show that all subgame perfect equilibria of this game result in the formation of an efficient network but the resulting net payoffs are asymmetric the second mechanism corrects this asymmetry through a two stage variant of the first mechanism we also discuss an extension of the basic model to cover the case of directed graphs and give conditions under which the proposed mechanisms are immune to deviations by coalitions

marriage and divorce comment the author comments on an article by h elizabeth peters concerning the impact of state laws particularly no fault divorce laws on divorce rates in the united states a reply by peters is included pp 686 93 annotation

multilateral stability and efficiency of trade agreements a network formation approach we study the endogenous network formation of bilateral and multilateral trade agreements by means of hypergraphs and introduce the equilibrium concept of multilateral stability we consider multi country settings with a firm in each country that produces a homogeneous good and competes as a cournot oligopolist in each market under endogenous tariffs we find that the existence of a multilateral trade agreement is always necessary for the stability of the trading system and that the formation of preferential trade agreements is always necessary for achieving global free trade we also find that global free trade is efficient but not necessarily the only multilaterally stable trade equilibrium when countries are symmetric heterogeneous in terms of market size we derive conditions under which such a conflict between overall welfare efficiency and stability occurs

networks in the modern economy mexican migrants in the u s labor market this paper attempts to identify job networks among mexican migrants in the u s labor market the empirical analysis uses data on migration patterns and labor market outcomes based on a sample of individuals belonging to multiple origin communities in mexico over a long period of time each community s network is measured by the proportion of the sampled individuals who are located at the destination the united states in any year we verify that the same individual is more likely to be employed and to hold a higher paying nonagricultural job when his network is exogenously larger by including individual fixed effects in the employment and occupation regressions and by using rainfall in the origin community as an instrument for the size of the network at the destination

systems competition and network effects this paper discusses firm behavior market performance and the public and private institutions that arise in systems markets i e markets where consumers use compatible components together to generate benefits in such markets which include communications networks and hardware software networks popular products are inherently more valuable these network effects can drive corporate strategies and are critical in understanding innovation in many high technology markets the discussion here emphasizes the dynamics of consumer adoption decisions in the presence of network effects competition between incompatible systems and how suppliers choose which components are compatible and which are not

the formation of a core periphery structure in heterogeneous financial networks recent empirical evidence suggests that nancial networks exhibit a core periphery network structure this paper aims at giving an economic explanation for the emergence of such a structure using network formation theory focusing on intermediation benets we nd that a core periphery network cannot be unilaterally stable when agents are homogeneous the best response dynamics converge to a unique unilaterally stable outcome ranging from an empty to denser networks as the costs of linking decrease a core periphery network structure can form endogenously however if we allow for heterogeneity among agents in size we show that our model can reproduce the observed core periphery structure in the dutch interbank market for reasonable parameter values

formation of buyer seller trade networks in a quality differentiated product market we examine the formation of buyer seller links when exchange can take place only if such a link exists sellers produce products of different qualities and multiple sellers can form a sellers association to pool their customers setting uniform prices buyers form trade links with individual sellers or sellers associations we show which buyer seller links will form and find the set of links that are stable and show how these links influence prices we also show that a trade network mismatch may occur where a high quality good remains unsold even without an economy wide excess supply of goods jel classification d40 d51 d82

networks of knowledge among unionized firms we develop a model of strategic networks in order to analyze how trade unions will affect the stability of r d networks through which knowledge is transmitted in an oligopolistic industry whenever firms settle wages the partially connected network is likely to emerge in the long run if and only if knowledge spillovers are large enough however when unions settle wages the complete network is the unique stable network in other words the stronger the union bargaining power is the more symmetric stable r d networks will be in terms of network efficiency the partially connected network when firms settle wages does not pareto dominate the complete network when unions settle wages and vice versa