Manipulations and repeated games in future markets

This chapter analyzes the possibility of manipulation in futures markets, concentrating on the effects that manipulation may have on their informational efficiency . We use the concept of manipulation as it arises in the study of noncooperative games with imperfect information . The problem can be summarized as follows : disclosure that is, (less anonymity) may prevent manipulation and therefore improve the informational efficiency of the market . On the other hand, disclosure (less anonymity) may restrict entry, and therefore produce an efficiency loss. There is, in this sense, a tradeoff between informational efficiency and free entry.futures; efficiency; futures markets; games; game theory; manipulation; imperfect information; disclosure; repeated games; one-shot game

Games of capacities : a (close) look to Nash Equilibria

The paper studies two games of capacity manipulation in hospital-intern markets. The focus is on the stability of Nash equilibrium outcomes. We provide minimal necessary and sufficient conditions guaranteeing the existence of pure strategy Nash Equilibria and the stability of outcomes

The effect of time manipulation on immersion in digital games

Many empirical studies look into identifying factors that influence the quality of experience in video games. In this paper, we present research into the effect of playing time and players’ perception of the time on their immersion in the game. We invited 20 participants to play a puzzle game Bejeweled 2 for 7 min. They played the game in two conditions, namely, correct time (timer was programmed to be exactly 7 min) and wrong time (the countdown was set to be for 6 min, but was presented as a 7 min timer to the player). Players’ immersion scores were measured after the game using the IEQ. The results show no significant difference in immersion scores between the two conditions and participants’ comments also revealed that they perceived no difference in playing time between the conditions. This suggests that there is a dissociation between gaming time and subjective experience of gaming. Further research is required to investigate the relationship between playing time and positive gaming experiences

Manipulating Tournaments in Cup and Round Robin Competitions

In sports competitions, teams can manipulate the result by, for instance, throwing games. We show that we can decide how to manipulate round robin and cup competitions, two of the most popular types of sporting competitions in polynomial time. In addition, we show that finding the minimal number of games that need to be thrown to manipulate the result can also be determined in polynomial time. Finally, we show that there are several different variations of standard cup competitions where manipulation remains polynomial.Comment: Proceedings of Algorithmic Decision Theory, First International Conference, ADT 2009, Venice, Italy, October 20-23, 200

Games of capacities : a (close) look to Nash Equilibria

The paper studies two games of capacity manipulation in hospital-intern markets. The focus is on the stability of Nash equilibrium outcomes. We provide minimal necessary and sufficient conditions guaranteeing the existence of pure strategy Nash Equilibria and the stability of outcomes.

Experimental Analysis of the Effects of Manipulations in Weighted Voting Games

Weighted voting games are classic cooperative games which provide compact representation for coalition formation models in human societies and multiagent systems. As useful as weighted voting games are in modeling cooperation among players, they are, however, not immune from the vulnerability of manipulations (i.e., dishonest behaviors) by strategic players that may be present in the games. With the possibility of manipulations, it becomes difficult to establish or maintain trust, and, more importantly, it becomes difficult to assure fairness in such games. For these reasons, we conduct careful experimental investigations and analyses of the effects of manipulations in weighted voting games, including those of manipulation by splitting, merging, and annexation . These manipulations involve an agent or some agents misrepresenting their identities in anticipation of gaining more power or obtaining a higher portion of a coalition\u27s profits at the expense of other agents in a game. We consider investigation of some criteria for the evaluation of game\u27s robustness to manipulation. These criteria have been defined on the basis of theoretical and experimental analysis. For manipulation by splitting, we provide empirical evidence to show that the three prominent indices for measuring agents\u27 power, Shapley-Shubik, Banzhaf, and Deegan-Packel, are all susceptible to manipulation when an agent splits into several false identities. We extend a previous result on manipulation by splitting in exact unanimity weighted voting games to the Deegan-Packel index, and present new results for excess unanimity weighted voting games. We partially resolve an important open problem concerning the bounds on the extent of power that a manipulator may gain when it splits into several false identities in non-unanimity weighted voting games. Specifically, we provide the first three non-trivial bounds for this problem using the Shapley-Shubik and Banzhaf indices. One of the bounds is also shown to be asymptotically tight. Furthermore, experiments on non-unanimity weighted voting games show that the three indices are highly susceptible to manipulation via annexation while they are less susceptible to manipulation via merging. Given that the problems of calculating the Shapley-Shubik and Banzhaf indices for weighted voting games are NP-complete, we show that, when the manipulators\u27 coalitions sizes are restricted to a small constant, manipulators need to do only a polynomial amount of work to find a much improved power gain for both merging and annexation, and then present two enumeration-based pseudo-polynomial algorithms that manipulators can use. Finally, we argue and provide empirical evidence to show that despite finding the optimal beneficial merge is an NP-hard problem for both the Shapley-Shubik and Banzhaf indices, finding beneficial merge is relatively easy in practice. Also, while it appears that we may be powerless to stop manipulation by merging for a given game, we suggest a measure, termed quota ratio, that the game designer may be able to control. Thus, we deduce that a high quota ratio decreases the number of beneficial merges

Games of Capacities: A (Close) Look to Nash Equilibria

The paper studies two games of capacity manipulation in hospital-intern markets. The focus is on the stability of Nash equilibrium outcomes. We provide minimal necessary and sufficient conditions guaranteeing the existence of pure strategy Nash Equilibria and the stability of outcomes.Stable Matchings, Capacity, Nash Equilibrium, Cycles.