Social Learning with Payoff Complementarities

We incorporate strategic complementarities into a multi-agent sequential choice model with observable actions and private information. In this framework agents are concerned with learning from predecessors, signalling to successors, and coordinating their actions with those of others. Coordination problems have hitherto been studied using static coordination games which do not allow for learning behavior. Social learning has been examined using games of sequential action under uncertainty, but in the absence of strategic complementarities (herding models). Our model captures the strategic behavior of static coordination games, the social learning aspect of herding models, and the signalling behavior missing from both of these classes of models in one unified framework. In sequential action problems with incomplete information, agents exhibit herd behavior if later decision makers assign too little importance to their private information, choosing instead to imitate their predecessors. In our setting we demonstrate that agents may exhibit either strong herd behavior (complete imitation) or weak herd behavior (overoptimism) and characterize the informational requirements for these distinct outcomes. We also characterize the informational requirements to ensure the possibility of coordination upon a risky but socially optimal action in a game with finite but unboundedly large numbers of players.

Evolutionary Sequential Trading

This paper analyzes an Easley and O'Hara (1992) type sequential trading model in an evolutionary setting. We assume that the memory of a market maker is limited, and that traders endogenously choose whether to acquire private information with a fixed cost. We show that the ratio of the informed traders is proportional to the width of the bid ask spread, and that the price converges to the strong-form efficient level exponentially.Market microstructure; Information asymmetry; Bayesian learning; Bid-ask spread; Evolutionary game theory

An Experimental Study of Information Revelation Policies in Sequential Auctions

Theoretical models of information asymmetry have identied a tradeoff between the desire to learn and the desire to prevent an opponent from learning private information. This paper reports a laboratory experiment that investigates if actual bidders account for this tradeoff, using a sequential procurement auction with private cost information and varying information revelation policies. Specically, the Complete Information Policy, where all submitted bids are revealed between auctions, is compared against the Incomplete Information Policy, where only the winning bid is revealed. The experimental results are largely consistent with the theoretical predictions. For example, bidders pool with other types to prevent an opponent from learning signicantly more often under a Complete Information Policy. Also as predicted, the procurer pays less when employing an Incomplete Information Policy only when the market is highly competitive. Bids are usually more aggressive than the risk neutral quantitative prediction, which is usually consistent with risk aversion.Complete and Incomplete Information Revelation Policies, Laboratory Study, Procurement Auction, Multistage Game

Beyond Ads: Sequential Decision-Making Algorithms in Law and Public Policy

We explore the promises and challenges of employing sequential decision-making algorithms - such as bandits, reinforcement learning, and active learning - in law and public policy. While such algorithms have well-characterized performance in the private sector (e.g., online advertising), their potential in law and the public sector remains largely unexplored, due in part to distinct methodological challenges of the policy setting. Public law, for instance, can pose multiple objectives, necessitate batched and delayed feedback, and require systems to learn rational, causal decision-making policies, each of which presents novel questions at the research frontier. We highlight several applications of sequential decision-making algorithms in regulation and governance, and discuss areas for needed research to render such methods policy-compliant, more widely applicable, and effective in the public sector. We also note the potential risks of such deployments and describe how sequential decision systems can also facilitate the discovery of harms. We hope our work inspires more investigation of sequential decision making in law and public policy, which provide unique challenges for machine learning researchers with tremendous potential for social benefit.Comment: Version 1 presented at Causal Inference Challenges in Sequential Decision Making: Bridging Theory and Practice, a NeurIPS 2021 Worksho

Learning optimization models in the presence of unknown relations

In a sequential auction with multiple bidding agents, it is highly challenging to determine the ordering of the items to sell in order to maximize the revenue due to the fact that the autonomy and private information of the agents heavily influence the outcome of the auction. The main contribution of this paper is two-fold. First, we demonstrate how to apply machine learning techniques to solve the optimal ordering problem in sequential auctions. We learn regression models from historical auctions, which are subsequently used to predict the expected value of orderings for new auctions. Given the learned models, we propose two types of optimization methods: a black-box best-first search approach, and a novel white-box approach that maps learned models to integer linear programs (ILP) which can then be solved by any ILP-solver. Although the studied auction design problem is hard, our proposed optimization methods obtain good orderings with high revenues. Our second main contribution is the insight that the internal structure of regression models can be efficiently evaluated inside an ILP solver for optimization purposes. To this end, we provide efficient encodings of regression trees and linear regression models as ILP constraints. This new way of using learned models for optimization is promising. As the experimental results show, it significantly outperforms the black-box best-first search in nearly all settings.Comment: 37 pages. Working pape