Manipulation in group argument evaluation.

Given an argumentation framework and a group of agents, the individuals may have divergent opinions on the status of the arguments. If the group needs to reach a common po- sition on the argumentation framework, the question is how the individual evaluations can be mapped into a collective one. This problem has been recently investigated in [1]. In this paper, we study under which conditions these operators are Pareto optimal and whether they are manipulable.Collective decision making; Argumentation; Judgment aggregation; Social choice theory;

Manipulation in Group Argument Evaluation.

Given an argumentation framework and a group of agents, the individuals may have divergent opinions on the status of the arguments. If the group needsto reach a common position on the argumentation framework, the question is how the individual evaluations can be mapped into a collective one. Thisproblem has been recently investigated by Caminada and Pigozzi. In this paper, we investigate the behaviour of two of such operators from a socialchoice-theoretic point of view. In particular, we study under which conditions these operators are Pareto optimal and whether they are manipulable.Social choice theory; Judgment aggregation; Argumentation; Collective decision making;

Pareto Optimality and Strategy Proofness in Group Argument Evaluation (Extended Version)

An inconsistent knowledge base can be abstracted as a set of arguments and a defeat relation among them. There can be more than one consistent way to evaluate such an argumentation graph. Collective argument evaluation is the problem of aggregating the opinions of multiple agents on how a given set of arguments should be evaluated. It is crucial not only to ensure that the outcome is logically consistent, but also satisfies measures of social optimality and immunity to strategic manipulation. This is because agents have their individual preferences about what the outcome ought to be. In the current paper, we analyze three previously introduced argument-based aggregation operators with respect to Pareto optimality and strategy proofness under different general classes of agent preferences. We highlight fundamental trade-offs between strategic manipulability and social optimality on one hand, and classical logical criteria on the other. Our results motivate further investigation into the relationship between social choice and argumentation theory. The results are also relevant for choosing an appropriate aggregation operator given the criteria that are considered more important, as well as the nature of agents' preferences

Aggregazione di giudizi

L’aggregazione di opinioni individuali per formare una decisione collettiva è l’oggetto di studio di Judgment Aggregation, una disciplina che coinvolge logica, economia, filosofia politica ed informatica. Il problema della presa di decisione collettiva a partire da posizioni individuali è comune nella vita di tutti i giorni e, sebbene la procedura da seguire sembri evidente, i risultati possono nascondere paradossi sorprendenti. La formalizzazione del problema dell’aggregazione di giudizi individuali ha permesso di portare un buon numero di risposte, di evidenziare legami con la teoria della scelta sociale e l’aggregazione di credenze, e di aprire la strada a nuove ricerche che permettono di applicare buona parte dei risultati ad altri paradigmi della decisione collettiva. Obiettivo di questo lavoro è di introdurre il problema dell’aggregazione di giudizi, motivare l’interesse per tali questioni, presentando i risultati principali ottenuti e indicando alcune delle piste di ricerca attuali.The aggregation of individual opinions to form a collective decision is the object of study of Judgment Aggregation, a discipline involving logic, economics, political philosophy and computer science. The problem of collective decision-making from individual positions arises in everyday life and, although the procedure to follow seems evident, the results can hide surprising paradoxes. The formalization of the problem of the aggregation of individual judgements has made it possible to bring a good number of answers, to highlight links with social choice theory and the aggregation of beliefs, and to pave the way to new research that allows to apply most of the results to other paradigms of collective decision-making. The aim of this work is to introduce the problem of judgement aggregation, to motivate interest in such issues, presenting the main results obtained so far and highlighting some of the current research tracks

09121 Abstracts Collection -- Normative Multi-Agent Systems

From 15.03. to 20.03.2009, the Dagstuhl Seminar 09121 ``Normative Multi-Agent Systems \u27\u27 was held in Schloss Dagstuhl~--~Leibniz Center for Informatics. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general

An opinion diffusion model with deliberation

In this article, we propose an agent-based model of opinion diffusion and voting where agents influence each other through deliberation. The model is inspired from social modeling as it describes a process of collective decision-making that iterates on a series of dyadic inter-individual influence steps and collective deliberation procedures. We study the evolution of opinions and the correctness of decisions taken within a group. We also aim at founding a comprehensive model to describe collective decision-making as a combination of two different paradigms: argumentation theory and agent-based influence models, which are not obvious to link since a formal translation and interpretation of their relationship is required. From a sequence of controlled simulations, we find that deliberation, modeled as an exchange of arguments, reduces the variance of opinions and the number of extremists, as long as not too much deliberation takes place during the decision-making process. Insofar as we define “correct” decisions as those whose supporting arguments survive deliberation, promoting deliberative discussion favors convergence towards correct decisions

Mixing Dyadic and Deliberative Opinion Dynamics in an Agent-Based Model of Group Decision-Making

International audienceIn this article, we propose an agent-based model of opinion diffusion and voting where influence among individuals and deliberation in a group are mixed. The model is inspired from social modeling, as it describes an iterative process of collective decision-making that repeats a series of interindividual influences and collective deliberation steps, and studies the evolution of opinions and decisions in a group. It also aims at founding a comprehensive model to describe collective decision-making as a combination of two different paradigms: argumentation theory and ABM-influence models, which are not obvious to combine as a formal link between them is required. In our model, we find that deliberation, through the exchange of arguments, reduces the variance of opinions and the proportion of extremists in a population as long as not too much deliberation takes place in the decision processes. Additionally, if we define the correct collective decisions in the system in terms of the arguments that should be accepted, allowing for more deliberation favors convergence towards the correct decisions

A partial taxonomy of judgment aggregation rules, and their properties

The literature on judgment aggregation is moving from studying impossibility results regarding aggregation rules towards studying specific judgment aggregation rules. Here we give a structured list of most rules that have been proposed and studied recently in the literature, together with various properties of such rules. We first focus on the majority-preservation property, which generalizes Condorcet-consistency, and identify which of the rules satisfy it. We study the inclusion relationships that hold between the rules. Finally, we consider two forms of unanimity, monotonicity, homogeneity, and reinforcement, and we identify which of the rules satisfy these properties

Multiagent Deontic Logic and its Challenges from a Normative Systems Perspective

This article gives an overview of several challenges studied in deontic logic, with an emphasis on challenges involving agents. We start with traditional modal deontic logic using preferences to address the challenge of contrary-toduty reasoning, and STIT theory addressing the challenges of non-deterministic actions, moral luck and procrastination. Then we turn to alternative normbased deontic logics detaching obligations from norms to address the challenge of Jørgensen’s dilemma, including the question how to derive obligations from a normative system when agents cannot assume that other agents comply with their norms. We discuss also some traditional challenges from the viewpoint of normative systems: when a set of norms may be termed ‘coherent’, how to deal with normative conflicts, how to combine normative systems and traditional deontic logic, how various kinds of permission can be accommodated, how meaning postulates and counts-as conditionals can be taken into account,how sets of norms may be revised and merged, and how normative systems can be combined with game theory. The normative systems perspective means that norms, not ideality or preference, should take the central position in deontic semantics, and that a semantics that represents norms explicitly provides a helpful tool for analysing, clarifying and solving the problems of deontic logic. We focus on the challenges rather than trying to give full coverage of related work, for which we refer to the handbook of deontic logic and normative systems

White Manipulation in Judgment Aggregation

Distributive systems consisting of autonomous and intelligent components need to be able to reason and make decisions based on the information these components share. Judgment aggregation investigates how individual judgments on logically connected propositions can be aggregated into a collective judgment on the same propositions. It is the case that seemingly reasonable aggregation procedures may force the group to hold an inconsistent judgment set. What happens when the agents realize that the group outcome will be inconsistent? We claim that, in order to avoid an untenable collective outcome, individuals may prefer to declare a non-truthful, less preferred judgment set. Thus, the prospect of an individual trying to manipulate the social outcome by submitting an insincere judgment set is turned from being an undesirable to a “virtuous” (or white) manipulation. We define white manipulation and present the initial study of it as a coordinated action of the whole group