AMU - AMSE
5-9 Boulevard Maurice Bourdet, CS 50498
13205 Marseille Cedex 1
Belhaj
Mohamed Belhaj
Faculty
,
Centrale Méditerranée
Status
Professor
Research fields
Finance
Game theory and social networks
Thesis
2005
,
University of Toulouse 1
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Contact
mohamed.belhaj[at]centrale-med.fr
+33(0)4 13 55 25 25
Address
Îlot Bernard du Bois
Publications
Targeting in networks under costly agreementsJournal article, Games and Economic Behavior, Volume 140, pp. 154-172, 2023
We consider agents organized in an undirected network of local complementarities. A principal with a fixed budget offers costly bilateral contracts in order to increase the sum of agents' effort. We study contracts rewarding effort exceeding the effort made in the absence of the principal. First, targeting a subgroup of the whole society becomes optimal under substantial contracting costs, which significantly increases the computational complexity of the principal's problem. In particular, under sufficiently low intensity of complementarities, a correspondence is established between optimal targeting and an NP-hard problem. Second, for any intensities of complementarities, the optimal unit returns offered to all targeted agents are positive for all contracting costs and in general heterogeneous, even though networks are undirected. Yet, heterogeneity never leads to negative returns, which implies that, with these linear payment schemes, coordination is never an issue for the principal.
The value of network information: Assortative mixing makes the differenceJournal article, Games and Economic Behavior, Volume 126, pp. 428-442, 2021
A monopoly sells a network good to a large population of consumers. We explore how the monopoly's profit and the consumer surplus vary with the arrival of public information about the network structure. The analysis reveals that, under homogeneous preferences for the good, degree assortativity ensures that information arrival increases both profit and consumer surplus. In contrast, heterogeneous preferences for the good can create a tension between consumer surplus and profit.
Group targeting under networked synergiesJournal article, Games and Economic Behavior, Volume 118, Issue C, pp. 29-46, 2019
A principal targets agents organized in a network of local complementarities, in order to increase the sum of agents' effort. We consider bilateral public contracts à la Segal (1999). The paper shows that the synergies between contracting and non-contracting agents deeply impact optimal contracts: they can lead the principal to contract with a subset of the agents, and to refrain from contracting with central agents.
Targeting the key player: An incentive-based approachJournal article, Journal of Mathematical Economics, Volume 79, Issue C, pp. 57-64, 2018
We consider a network game with local complementarities. A policymaker, aiming at minimizing or maximizing aggregate effort, contracts with a single agent on the network to trade effort change against transfer. The policymaker has to find the best agent and the optimal contract to offer. Our study shows that for all utilities with linear best-responses, it only takes two statistics about the position of each agent on the network to identify the key player: the Bonacich centrality and the self-loop centrality. We also characterize key players under linear quadratic utilities for various contractual arrangements.
Efficient networks in games with local complementaritiesJournal article, Theoretical Economics, Volume 11, Issue 1, pp. 357-380, 2016
We address the problem of a planner looking for the efficient network when agents play a network game with local complementarities and links are costly. We show that for general network cost functions, efficient networks belong to the class of Nested-Split Graphs. Next, we refine our results and find that, depending on the specification of the network cost function, complete networks, core-periphery networks, dominant group architectures, quasi-star and quasi-complete networks can be efficient.
Network games under strategic complementaritiesJournal article, Games and Economic Behavior, Volume 88, Issue C, pp. 310-319, 2014
We study network games under strategic complementarities. Agents are embedded in a fixed network. They choose a positive, continuous action and interact with their network neighbors. Interactions are positive and actions are bounded from above. We first derive new sufficient conditions for uniqueness, covering all concave as well as some non-concave best responses. We then study the relationship between position and action and identify situations where a more central agent always plays a higher action in equilibrium. We finally analyze comparative statics. We show that a shock may not propagate throughout the entire network and uncover a general pattern of decreasing interdependence.
Competing Activities in Social NetworksJournal article, The B.E. Journal of Economic Analysis & Policy, Volume 14, Issue 4, pp. 36, 2014
We consider a society in which each agent has one unit of a resource to allocate between two activities. Agents are organized in a social network, and each activity generates complementarities between neighbors. We find multiplicity of equilibrium for high intensity of interaction, and we characterize equilibria in terms of specialization and polarization. Overall, results reveal the crucial role played by network geometry. The results also suggest that the structure of the social network should be taken into account for the design of a public policy in favor of a specific activity.
Risk-Taking and Risk-Sharing Incentives under Moral HazardJournal article, American Economic Journal: Microeconomics, Volume 6, Issue 1, pp. 58-90, 2014
This paper explores the effect of moral hazard on both risk-taking and informal risk-sharing incentives. Two agents invest in their own project, each choosing a level of risk and effort, and share risk through transfers. This can correspond to farmers in developing countries, who share risk and decide individually upon the adoption of a risky technology. The paper mainly shows that the impact of moral hazard on risk crucially depends on the observability of investment risk, whereas the impact on transfers is much more utility dependent.
Strategic interaction and aggregate incentivesJournal article, Journal of Mathematical Economics, Volume 49, Issue 3, pp. 183-188, 2013
We consider a model of interdependent efforts, with linear interaction and lower bound on effort. Our setting encompasses asymmetric interaction and heterogeneous agents’ characteristics. We examine the impact of a rise of cross-effects on aggregate efforts. We show that the sign of the comparative static effects is related to a condition of balancedness of the interaction. Moreover, we point out that asymmetry and heterogeneous characteristics are sources of non-monotonic variation of aggregate efforts.
Comments on ‘On Optimal Dividend Payouts Under Jump-Diffusion Risk Processes‘Journal article, Stochastic models, Volume 28, Issue 1, pp. 185-186, 2012
