text: In a system of interdependent users, the security of an entity is affected not only by that user’s investment in security measures, but also by the positive externality of the security decisions of (some of) the other users. The provision of security in such system is therefore modeled as a public good provision problem, and is referred to as a security game. In this paper, we compare two well-known incentive mechanisms in this context for incentivizing optimal security investments among users, namely the Pivotal and the Externality mechanisms. The taxes in a Pivotal mechanism are designed to ensure users’ voluntary participation, while those in an Externality mechanism are devised to maintain a balanced budget. We first show the more general result that, due to the nonexcludable nature of security, no mechanism can incentivize the socially optimal investment profile, while at the same time ensuring voluntary participation and maintaining a balanced budget for all instances of security games. To further illustrate, we apply the Pivotal and Externality mechanisms to the special case of weighted total effort interdependence models, and identify some of the effects of varying interdependency between users on the budget deficit in the Pivotal mechanism, as well as on the participation incentives in the Externality mech
  @cite_21: This paper considers incentives to provide goods that are non-excludable along social or geographic links. We find, first, that networks can lead to specialization in public good provision. In every social network there is an equilibrium where some individuals contribute and others free ride. In many networks, this extreme is the only outcome. Second, specialization can benefit society as a whole. This outcome arises when contributors are linked, collectively, to many agents. Finally, a new link increases access to public goods, but reduces individual incentives to contribute. Hence, overall welfare can be higher when there are holes in a network.
  @cite_22: Finite population non-cooperative games with linear-quadratic utilities, where each player decides how much action she exerts, can be interpreted as a network game with local payoff complementarities, together with a globally uniform payoff substitutability component and an ownconcavity effect. For these games, the Nash equilibrium action of each player is proportional to her Bonacich centrality in the network of local complementarities, thus establishing a bridge with the sociology literature on social networks. This Bonacich-Nash linkage implies that aggregate equilibrium increases with network size and density. We then analyze a policy that consists of targeting the key player, that is, the player who, once removed, leads to the optimal change in aggregate activity. We provide a geometric characterization of the key player identifed with an inter-centrality measure, which takes into account both a player's centrality and her contribution to the centrality of the others.
  @cite_11: We consider a finite population simultaneous move game with heterogeneous interaction modes across different pairs of players. We allow for general interaction patterns, but restrict our analysis to games whose pure strategy Nash equilibrium conditions boil down to a set of piece-wise linear conditions, so that an equilibrium is a solution to a linear complementarity problem. We introduce a new class of games for which a suitable linear transformation of the original interaction matrix induces a game with complementarities. We provide general moderation conditions on the interaction matrix such that a game in this class has a unique Nash equilibrium, that we are able to characterize by means of a closed-form expression involving a generalized version of the Katz network measure of node centrality.
summary: @cite_21 introduces a network model of public goods, and studies different features of its Nash equilibria. This model is equivalent to a total effort game with linear investment costs and a general interdependence graph. The authors show that these games always have a Nash equilibrium; i.e., one in which users are either specialists exerting full effort (equivalent to main investors in our terminology), or free-riders. They show that such equilibria correspond to maximal independent sets of the graph, and that specialized equilibira may lead to higher welfare compared to other (distributed) Nash equilibria. Similarly, @cite_22 studies the Nash equilibrium of a linear quadratic interdependence model, and relates the equilibrium effort levels to the nodes' Bonacich centrality in a suitably defined matrix of local complementarities. The work in @cite_11 generalizes these results by studying existence, uniqueness, and closed form of the Nash equilibrium in a broader class of games for which best-responses are linear in other players' actions. All the aforementioned work focuses on the Nash equilibrium in public good provision environments.