Suppose two players wish to divide a finite set of indivisible items, over which each distributes a specified number of points. Assuming the utility of a player’s bundle is the sum of the points it assigns to the items it contains, we analyze what divisions are fair. We show that if there is an envy-free (EF) allocation of the items, two other desirable properties—Pareto-optimality (PO) and Maximinality (MM)—can also be satisfied, rendering these three properties compatible. But there may be no (...) EF division, in which case some division must satisfy a modification of Bentham’s (1789/2017) “greatest satisfaction of the greatest number” property, called maximum Nash welfare (MNW), that satisfies PO. However, an MNF division may be neither MM nor EFX, which is a weaker form of EF. We conjecture that there is always an EFX allocation that satisfies MM, ensuring that an allocation is maximin, precisely the property that Rawls (1971/1999) championed. We discuss four broader philosophical implications of our more technical analysis. (shrink)

Multi-winner elections, for example, the election of members to a committee, are now quite common, and include the interesting subclass of elections with a variable number of winners, or VNW elections. In VNW elections, voters determine how many winners there are, as well as which candidates win. Common VNW elections include elections to bestow honorary status, such as enshrinement in a hall of fame, and elections to determine a shortlist of, say, job candidates for interviews. Such elections are VNW elections (...) whenever the number of winners is not specified in advance. Multi-winner elections are often conducted by adapting standard procedures for single-winner elections. Approval balloting is particularly appropriate for multi-winner elections, as every ballot, and the set of winners, are subsets of the set of all candidates. Many methods of counting approval ballots appropriate to VNW elections are reviewed and illustrated, and their properties—desirable and undesirable—discussed. (shrink)

A cornerstone of game theory is backward induction, whereby players reason backward from the end of a game in extensive form to the beginning in order to determine what choices are rational at each stage of play. Truels, or three-person duels, are used to illustrate how the outcome can depend on (1) the evenness/oddness of the number of rounds (the parity problem) and (2) uncertainty about the endpoint of the game (the uncertainty problem). Since there is no known endpoint in (...) the latter case, an extension of the idea of backward induction is used to determine the possible outcomes. The parity problem highlights the lack of robustness of backward induction, but it poses no conflict between foundational principles. On the other hand, two conflicting views of the future underlie the uncertainty problem, depending on whether the number of rounds is bounded (the players invariably shoot from the start) or unbounded (they may all cooperate and never shoot, despite the fact that the truel will end with certainty and therefore be effectively bounded). Some real-life examples, in which destructive behavior sometimes occurred and sometimes did not, are used to illustrate these differences, and some ethical implications of the analysis are discussed. (shrink)

Deterrence means threatening to retaliate against an attack in order to deter it in the first place. The central problem with a policy of deterrence is that the threat of retaliation may not be credible if retaliation leads to a worse outcome - perhaps a nuclear holocaust - than a side would suffer from absorbing a limited first strike and not retaliating. - The optimality of deterrence is analyzed by means of a Deterrence Game based on Chicken, in which each (...) player chooses a probability (or level) of preemption, and of retaliation if preempted. The Nash equilibria, or stable outcomes, in this game are compared with those in a Star Wars Game, in which the preemption and retaliation levels are constrained by the defensive capabilities of each side. Unlike threats in the Deterrence Game, which can always stabilize the cooperative outcome, mutual preemption emerges as an equilibrium in the Star Wars Game, underscoring the problem - particularly if defensive capabilities are unbalanced - that deterrence will be subverted by the development of Star Wars. (shrink)

Issues that arise in using game theory to model national security problems are discussed, including positing nation-states as players, assuming that their decision makers act rationally and possess complete information, and modeling certain conflicts as two-person games. A generic two-person game called the Conflict Game, which captures strategic features of such variable-sum games as Chicken and Prisoners'' Dilemma, is then analyzed. Unlike these classical games, however, the Conflict Game is a two-stage game in which each player can threaten to retaliate (...) — and carry out this threat in the second stage — if its opponent chose noncooperation in the first stage.Conditions for the existence of different pure-strategy Nash equilibria, or stable outcomes, are found, and these results are extended to situations in which the players can select mixed strategies (i.e., make probabilistic threats or choices). Although the Conflict Game sheds light on the rational foundations underlying arms races, nuclear deterrence, and other strategic situations, more detailed assumptions are required to tie this generic game to specific conflicts. (shrink)

1. Introduction The policy of deterrence, at least to avert nuclear war between the superpowers, has been a controversial one. The main controversy arises from the threat of each side to visit destruction on the other in response to an initial attack. This threat would seem irrational if carrying it out would lead to a nuclear holocaust – the worst outcome for both sides. Instead, it would seem better for the side attacked to suffer some destruction rather than to retaliate (...) in kind and, in the process of devastating the other side, seal its own doom in an all-out nuclear exchange. Yet, the superpowers persist in their adherence to deterrence, by which we mean a policy of threatening to retaliate to an attack by the other side in order to deter such an attack in the first place. To be sure, nuclear doctrine for implementing deterrence has evolved over the years, with such appellations as “massive retaliation,” “flexible response,” “mutual assured destruction”, and “counterforce” giving some flavor of the changes in United States strategic thinking. All such doctrines, however, entail some kind of response to a Soviet nuclear attack. They are operationalized in terms of preselected targets to be hit, depending on the perceived nature and magnitude of the attack. Thus, whether U.S. strategic policy at any time stresses a retaliatory attack on cities and industrial centers or on weapons systems and armed forces, the certainty of a response of some kind to an attack is not the issue. (shrink)

A hybrid preference framework is proposed for strategic conflict analysis to integrate preference strength and preference uncertainty into the paradigm of the graph model for conflict resolution (GMCR) under multiple decision makers. This structure offers decision makers a more flexible mechanism for preference expression, which can include strong or mild preference of one state or scenario over another, as well as equal preference. In addition, preference between two states can be uncertain. The result is a preference framework that is more (...) general than existing models which consider preference strength and preference uncertainty separately. Within the hybrid preference structure, four kinds of stability are defined as solution concepts and a post-stability analysis, called status quo analysis, which can be used to track the evolution of a given conflict. Algorithms are provided for implementing the key inputs of stability analysis and status quo analysis within the extended preference structure. The new stability concepts under the hybrid preference structure can be used to model complex strategic conflicts arising in practical applications, and can provide new insights for the conflicts. The method is illustrated using the conflict over proposed bulk water exports from Lake Gisborne in Newfoundland, Canada. (shrink)

Stability definitions for describing human behavior under conflict when coalitions may form are generalized within the Graph Model for Conflict Resolution and algebraic formulations of these definitions are provided to allow computer implementation. The more general definitions of coalitional stabilities relax the assumption of transitive graphs capturing movements under the control of decision makers, either independently or cooperatively, and allow the convenient expansion to the case of coalitions of the four basic individual stabilities consisting of Nash stability, general metarationality, symmetric (...) metarationality, and sequential stability. To permit the various coalitional stabilities to be efficiently calculated and conveniently encoded within a decision support system, algebraic expressions for the coalitional stabilities are provided in this research. Furthermore, a range of the theorems establish the mathematical credibility of employing the innovative algebraic approach to conflict resolution when coalitions are present. Finally, a conflict over the proposed exportation of bulk water from Lake Gisborne within the Canadian Province of Newfoundland and Labrador is modelled and analyzed to illustrate the practical application of the different coalitional stabilities and the strategic insights they provide. (shrink)

A new approach to policy analysis is formulated within the framework of the graph model for conflict resolution. A policy is defined as a plan of action for a decision maker (DM) that specifies the DM’s intended action starting at every possible state in a graph model of a conflict. Given a profile of policies, a Policy Stable State (PSS) is a state that no DM moves away from (according to its policy), and such that no DM would prefer to (...) change its policy given the policies of the other DMs. The profile of policies associated to a PSS is called a Policy Equilibrium. Properties of PSSs are developed, and a refinement is suggested that restricts DMs to policies that are credible in that they are in the DM’s immediate interest. Relationships with existing stability definitions in the graph model for conflict resolution are then explored. (shrink)

Contested Pile methods are two-phase procedures for the fair allocation of indivisible items to two players. In the Generation Phase, items over which the players’ preferences differ widely enough are allocated. “Contested” items are placed in the Contested Pile, which is then allocated in the Splitting Phase. Each phase can be carried out using several different techniques; we perform a comprehensive analysis of the resulting design variants using a computational model. The properties of fairness and efficiency, generally achieved in the (...) Generation Phase, must be traded off against robustness to manipulation. We find that the recently developed Undercut procedure for the Splitting Phase outperforms alternative methods in both fairness and efficiency. In general, procedures that keep the Contested Pile relatively small and incorporate the Undercut procedure score well in both fairness and efficiency, but are prone to manipulation. (shrink)