Effort Maximization in Asymmetric N-Person Contest Games

This paper provides existence and characterization of the optimal contest success function under the condition that the objective of the contest designer is total effort maximization among n heterogeneous players. Heterogeneity of players makes active participation of a player in equilibrium endogenous with respect to the specific contest success function adopted by the contest designer. Hence, the aim of effort maximization implies the identification of those players who should be excluded from making positive efforts. We give a general proof for the existence of an optimal contest success function and provide an algorithm for the determination of the set of actively participating players. This is turn allows to determine optimal efforts in closed form. An important general feature of the solution is that maximization of total effort requires at least three players to be active

Population-Based Rates of Revision of Primary Total Hip Arthroplasty: A Systematic Review

Background: Most research on failure leading to revision total hip arthroplasty (THA) is reported from single centers. We searched PubMed between January 2000 and August 2010 to identify population- or community-based studies evaluating ten-year revision risks. We report ten-year revision risk using the Kaplan-Meier method, stratifying by age and fixation technique. Results: Thirteen papers met the inclusion criteria. Cemented prostheses had Kaplan-Meier estimates of revision-free implant survival of ten years ranging from 88 % to 95%; uncemented prostheses had Kaplan-Meier estimates from 80 % to 85%. Estimates ranged from 72 % to 86 % in patients less than 60 years old and from 90 to 96 % in older patients. Conclusion: Data reported from national registries suggest revision risks of 5 to 20 % ten years following primary THA. Revision risks are lower in older THA recipients. Uncemented implants may have higher ten-year rates of revision, regardless of age

Alliance Formation in Contests with Incomplete Information

This paper studies a contest in which players with unobservable types may form an alliance in a pre-stage of the game to join their forces and compete for a prize. We characterize the pure strategy equilibria of this game of incomplete information. We show that if the formation of an alliance is voluntary, players do not reveal private information in the process of alliance formation in any equilibrium. In this case there exists a pooling equilibrium without alliances with a unique effort choice in the contest and there exist equilibria in which all types prefer to form an alliance. If the formation of an alliance can be enforced by one player with positive probability there exists an equilibrium in which only the low types prefer to form an alliance.Der vorliegende Aufsatz untersucht ein Modell, in welchem Agenten mit unbeobachtbaren Typen ihre Kräfte in Allianzen vereinen können, bevor sie in einen Wettstreit um eine Ressource eintreten. Wir beschreiben die Gleichgewichte in reinen Strategien dieses Spiels unter unvollständiger Information. Für den Fall des freiwilligen Eintritts in eine Allianz zeigen wir, dass die Spieler in keinem Gleichgewicht private Information während der Bildung der Allianz offenbaren. In diesem Fall existiert ein vereinigendes Gleichgewicht ohne Allianz, in dem die Spieler eine eindeutige, typen-abhängige Investition im Wettstreit wählen. Es existieren auch vereinigende Gleichgewichte, in welchen es alle Spieler-Typen strikt bevorzugen, in eine Allianz einzutreten. Falls eine Allianz seitens eines Spielers mit positiver Wahrscheinlichkeit erzwungen werden kann, existiert ein trennendes Gleichgewicht, in welchem nur die schwachen Spieler-Typen in die Allianz eintreten wollen

Potential competition and coordination in a market-entry game

entry coordination, investment rivalry, potential competition, D43, D72, L13,