David Thompson - Academia.edu (original) (raw)

Papers by David Thompson

Research paper thumbnail of Empirical analysis of plurality election equilibria

ABSTRACT Voting is widely used to aggregate the different preferences of agents, even though thes... more ABSTRACT Voting is widely used to aggregate the different preferences of agents, even though these agents are often able to manipulate the outcome through strategic voting. Most research on manipulation of voting methods studies (1) limited solution concepts, (2) limited preferences, or (3) scenarios with a few manipulators that have a common goal. In contrast, we study voting in plurality elections through the lens of Nash equilibrium, which allows for the possibility that any number of agents, with arbitrary different goals, could all be manipulators. This is possible thanks to recent advances in (Bayes-)Nash equilibrium computation for large games. Although plurality has numerous pure-strategy Nash equilibria, we demonstrate how a simple equilibrium refinement---assuming that agents only deviate from truthfulness when it will change the outcome---dramatically reduces this set. We also use symmetric Bayes-Nash equilibria to investigate the case where voters are uncertain of each others' preferences. This refinement does not completely eliminate the problem of multiple equilibria. However, it does show that even when agents manipulate, plurality still tends to lead to good outcomes (e.g., Condorcet winners, candidates that would win if voters were truthful, outcomes with high social welfare).

Research paper thumbnail of Computing Nash Equilibria of Action-Graph Games via Support Enumeration

Lecture Notes in Computer Science, 2011

Action-graph games (AGGs) are a fully expressive game representation which can compactly express ... more Action-graph games (AGGs) are a fully expressive game representation which can compactly express both strict and context-specific independence between players' utility functions. Actions are represented as nodes in a graph G, and the payoff to an agent who chose the action s depends only on the numbers of other agents who chose actions connected to s. We present algorithms for computing both symmetric and arbitrary equilibria of AGGs using a continuation method. We analyze the worst-case cost of computing the Jacobian of the payoff function, the exponential-time bottleneck step, and in all cases achieve exponential speedup. When the indegree of G is bounded by a constant and the game is symmetric, the Jacobian can be computed in polynomial time.

Research paper thumbnail of Empirical Aspects of Plurality Election Equilibria

Voting is widely used to aggregate the different preferences of agents, even though these agents ... more Voting is widely used to aggregate the different preferences of agents, even though these agents are often able to manipulate the outcome through strategic voting. Most research on manipulation of voting methods studies (1) limited solution concepts, (2) limited preferences, or (3) scenarios with a few manipulators that have a common goal. In contrast, we study voting in plurality elections through the lens of Nash equilibrium, which allows for the possibility that any number of agents, with arbitrary different goals, could all be manipulators. This is possible thanks to recent advances in (Bayes-)Nash equilibrium computation for large games. Although plurality has numerous pure-strategy Nash equilibria, we demonstrate how a simple equilibrium refinementassuming that agents only deviate from truthfulness when it will change the outcome-dramatically reduces this set. We also use symmetric Bayes-Nash equilibria to investigate the case where voters are uncertain of each others' preferences. This refinement does not completely eliminate the problem of multiple equilibria. However, it does show that even when agents manipulate, plurality still tends to lead to good outcomes (e.g., Condorcet winners, candidates that would win if voters were truthful, outcomes with high social welfare).

Research paper thumbnail of Revenue optimization in the generalized second-price auction

Proceedings of the fourteenth ACM conference on Electronic commerce - EC '13, 2013

ABSTRACT We consider the optimization of revenue in advertising auctions based on the generalized... more ABSTRACT We consider the optimization of revenue in advertising auctions based on the generalized second-price (GSP) paradigm, which has become a de facto standard. We examine several different GSP variants (including squashing and different types of reserve prices), and consider how to set their parameters optimally. One intriguing finding is that charging each advertiser the same per-click reserve price ("unweighted reserve prices") yields dramatically more revenue than the quality-weighted reserve prices that have become common practice. This result is robust, arising both from theoretical analysis and from two different kinds of computational experiments. We also identify a new GSP variant that is revenue optimal in restricted settings. Finally, we study how squashing and reserve prices interact, and how equilibrium selection affects the revenue of GSP when features such as reserves or squashing are applied.

Research paper thumbnail of Empirical analysis of plurality election equilibria

ABSTRACT Voting is widely used to aggregate the different preferences of agents, even though thes... more ABSTRACT Voting is widely used to aggregate the different preferences of agents, even though these agents are often able to manipulate the outcome through strategic voting. Most research on manipulation of voting methods studies (1) limited solution concepts, (2) limited preferences, or (3) scenarios with a few manipulators that have a common goal. In contrast, we study voting in plurality elections through the lens of Nash equilibrium, which allows for the possibility that any number of agents, with arbitrary different goals, could all be manipulators. This is possible thanks to recent advances in (Bayes-)Nash equilibrium computation for large games. Although plurality has numerous pure-strategy Nash equilibria, we demonstrate how a simple equilibrium refinement---assuming that agents only deviate from truthfulness when it will change the outcome---dramatically reduces this set. We also use symmetric Bayes-Nash equilibria to investigate the case where voters are uncertain of each others' preferences. This refinement does not completely eliminate the problem of multiple equilibria. However, it does show that even when agents manipulate, plurality still tends to lead to good outcomes (e.g., Condorcet winners, candidates that would win if voters were truthful, outcomes with high social welfare).

Research paper thumbnail of Computing Nash Equilibria of Action-Graph Games via Support Enumeration

Lecture Notes in Computer Science, 2011

Action-graph games (AGGs) are a fully expressive game representation which can compactly express ... more Action-graph games (AGGs) are a fully expressive game representation which can compactly express both strict and context-specific independence between players' utility functions. Actions are represented as nodes in a graph G, and the payoff to an agent who chose the action s depends only on the numbers of other agents who chose actions connected to s. We present algorithms for computing both symmetric and arbitrary equilibria of AGGs using a continuation method. We analyze the worst-case cost of computing the Jacobian of the payoff function, the exponential-time bottleneck step, and in all cases achieve exponential speedup. When the indegree of G is bounded by a constant and the game is symmetric, the Jacobian can be computed in polynomial time.

Research paper thumbnail of Empirical Aspects of Plurality Election Equilibria

Voting is widely used to aggregate the different preferences of agents, even though these agents ... more Voting is widely used to aggregate the different preferences of agents, even though these agents are often able to manipulate the outcome through strategic voting. Most research on manipulation of voting methods studies (1) limited solution concepts, (2) limited preferences, or (3) scenarios with a few manipulators that have a common goal. In contrast, we study voting in plurality elections through the lens of Nash equilibrium, which allows for the possibility that any number of agents, with arbitrary different goals, could all be manipulators. This is possible thanks to recent advances in (Bayes-)Nash equilibrium computation for large games. Although plurality has numerous pure-strategy Nash equilibria, we demonstrate how a simple equilibrium refinementassuming that agents only deviate from truthfulness when it will change the outcome-dramatically reduces this set. We also use symmetric Bayes-Nash equilibria to investigate the case where voters are uncertain of each others' preferences. This refinement does not completely eliminate the problem of multiple equilibria. However, it does show that even when agents manipulate, plurality still tends to lead to good outcomes (e.g., Condorcet winners, candidates that would win if voters were truthful, outcomes with high social welfare).

Research paper thumbnail of Revenue optimization in the generalized second-price auction

Proceedings of the fourteenth ACM conference on Electronic commerce - EC '13, 2013

ABSTRACT We consider the optimization of revenue in advertising auctions based on the generalized... more ABSTRACT We consider the optimization of revenue in advertising auctions based on the generalized second-price (GSP) paradigm, which has become a de facto standard. We examine several different GSP variants (including squashing and different types of reserve prices), and consider how to set their parameters optimally. One intriguing finding is that charging each advertiser the same per-click reserve price ("unweighted reserve prices") yields dramatically more revenue than the quality-weighted reserve prices that have become common practice. This result is robust, arising both from theoretical analysis and from two different kinds of computational experiments. We also identify a new GSP variant that is revenue optimal in restricted settings. Finally, we study how squashing and reserve prices interact, and how equilibrium selection affects the revenue of GSP when features such as reserves or squashing are applied.