Propositional Opinion Diffusion

We present a formal model of opinion diffusion and formation which combines notions from social network analysis together with concepts and techniques from judgment aggregation and merging. The model allows us to study the propagation of individual opinions, represented in the form of yes/no answers to a set of multiple binary issues, in a multiagent system linked by an influence network. The process is iterative with discrete time. We are interested in characterizing properties of the network structure which guarantee convergence of the iterative process for every initial configuration of the agents' opinions, and in developing tractable algorithms for computing the set of opinions at convergence

Liquid Democracy: An Analysis in Binary Aggregation and Diffusion

The paper proposes an analysis of liquid democracy (or, delegable proxy voting) from the perspective of binary aggregation and of binary diffusion models. We show how liquid democracy on binary issues can be embedded into the framework of binary aggregation with abstentions, enabling the transfer of known results about the latter---such as impossibility theorems---to the former. This embedding also sheds light on the relation between delegation cycles in liquid democracy and the probability of collective abstentions, as well as the issue of individual rationality in a delegable proxy voting setting. We then show how liquid democracy on binary issues can be modeled and analyzed also as a specific process of dynamics of binary opinions on networks. These processes---called Boolean DeGroot processes---are a special case of the DeGroot stochastic model of opinion diffusion. We establish the convergence conditions of such processes and show they provide some novel insights on how the effects of delegation cycles and individual rationality could be mitigated within liquid democracy. The study is a first attempt to provide theoretical foundations to the delgable proxy features of the liquid democracy voting system. Our analysis suggests recommendations on how the system may be modified to make it more resilient with respect to the handling of delegation cycles and of inconsistent majorities

Sharing as speech act

Social media platforms allow users to perform different speech acts: status updates could be assertives, a like is an expressive, a friendship request is a directive, and so on. But sharing (or "retweeting") seems to lack a fixed illocutive status: this explains why present controversies concerning the sharing of misinformation have been debated in legal procedure and discussed from the point of view of personal responsibility without reaching a general consensus. The premise of this paper is that the diffusion of false or unwarranted information could be better analyzed if we consider sharing a precisely definable speech act. I will describe some dominant interpretations of the act of sharing that are not, however, sufficient to fully explain it. As an alternative, it will be shown that there is a specific illocutive structure of the act of sharing, which not only consists in asserting the "shareworthiness" or the relevance of a content, but is primarily comparable to an "attention-orienting" directive

Collective decision-making with goals

Des agents devant prendre une décision collective sont souvent motivés par des buts individuels. Dans ces situations, deux aspects clés doivent être abordés : sélectionner une alternative gagnante à partir des voix des agents et s'assurer que les agents ne manipulent pas le résultat. Cette thèse étudie l'agrégation et la dimension stratégique des décisions collectives lorsque les agents utilisent un langage représenté de manière compacte. Nous étudions des langages de type logique : de la logique propositionnelle aux CP-nets généralisés, en passant par la logique temporelle linéaire (LTL). Notre principale contribution est l'introduction d'un cadre de vote sur les buts, dans lequel les agents soumettent des buts individuels exprimés comme des formules de la logique propositionnelle. Les fonctions d'agrégation classiques issues du vote, de l'agrégation de jugements et de la fusion de croyances sont adaptées et étudiées de manière axiomatique et computationnelle. Les propriétés axiomatiques connues dans la littérature sur la théorie du choix social sont généralisées à ce nouveau type d'entrée, ainsi que les problèmes de complexité visant à déterminer le résultat du vote. Une autre contribution importante est l'étude de l'agrégation des CP-nets généralisés, c'est-à-dire des CP-nets où la précondition de l'énoncé de préférence est une formule propositionnelle. Nous utilisons différents agrégateurs pour obtenir un classement collectif des résultats possibles. Grâce à cette thèse, deux axes de recherche sont ainsi reliés : l'agrégation des CP-nets classiques et la généralisation des CP-nets à des préconditions incomplètes. Nous contribuons également à l'étude du comportement stratégique dans des contextes de prise de décision collective et de théorie des jeux. Le cadre du vote basé sur les buts est de nouveau étudié sous l'hypothèse que les agents peuvent décider de mentir sur leur but s'ils obtiennent ainsi un meilleur résultat. L'accent est mis sur trois règles de vote majoritaires qui se révèlent manipulables. Par conséquent, nous étudions des restrictions à la fois sur le langage des buts et sur les stratégies des agents en vue d'obtenir des résultats de votes non manipulables. Nous présentons par ailleurs une extension stratégique d'un modèle récent de diffusion d'opinion sur des réseaux d'influence. Dans les jeux d'influence définis ici, les agents ont comme but des formules en LTL et ils peuvent choisir d'utiliser leur pouvoir d'influence pour s'assurer que leur but est atteint. Des solutions classiques telles que la stratégie gagnante sont étudiées pour les jeux d'influence, en relation avec la structure du réseau et les buts des agents. Enfin, nous introduisons une nouvelle classe de concurrent game structures (CGS) dans laquelle les agents peuvent avoir un contrôle partagé sur un ensemble de variables propositionnelles. De telles structures sont utilisées pour interpréter des formules de logique temporelle en temps alternés (ATL), grâce auxquelles on peut exprimer l'existence d'une stratégie gagnante pour un agent dans un jeu itéré (comme les jeux d'influence mentionnés ci-dessus). Le résultat principal montre qu'un CGS avec contrôle partagé peut être représenté comme un CGS avec contrôle exclusif. En conclusion, cette thèse contribue au domaine de la prise de décision collective en introduisant un nouveau cadre de vote basé sur des buts propositionnels. Elle présente une étude de l'agrégation des CP-nets généralisés et une extension d'un cadre de diffusion d'opinion avec des agents rationnels qui utilisent leur pouvoir d'influence. Une réduction du contrôle partagé à un contrôle exclusif dans les CGS pour l'interprétation des logiques du raisonnement stratégique est également proposée. Par le biais de langages logiques divers, les agents peuvent ainsi exprimer buts et préférences sur la décision à prendre, et les propriétés souhaitées pour le processus de décision peuvent en être garanties.Agents having to take a collective decision are often motivated by individual goals. In such scenarios, two key aspects need to be addressed. The first is defining how to select a winning alternative from the expressions of the agents. The second is making sure that agents will not manipulate the outcome. Agents should also be able to state their goals in a way that is expressive, yet not too burdensome. This dissertation studies the aggregation and the strategic component of multi-agent collective decisions where the agents use a compactly represented language. The languages we study are all related to logic: from propositional logic, to generalized CP-nets and linear temporal logic (LTL). Our main contribution is the introduction of the framework of goal-based voting, where agents submit individual goals expressed as formulas of propositional logic. Classical aggregation functions from voting, judgment aggregation, and belief merging are adapted to this setting and studied axiomatically and computationally. Desirable axiomatic properties known in the literature of social choice theory are generalized to this new type of propositional input, as well as the standard complexity problems aimed at determining the result. Another important contribution is the study of the aggregation of generalized CP-nets coming from multiple agents, i.e., CP-nets where the precondition of the preference statement is a propositional formula. We use different aggregators to obtain a collective ordering of the possible outcomes. Thanks to this thesis, two lines of research are thus bridged: the one on the aggregation of complete CP-nets, and the one on the generalization of CP-nets to incomplete preconditions. We also contribute to the study of strategic behavior in both collective decision-making and game-theoretic settings. The framework of goal-based voting is studied again under the assumption that agents can now decide to submit an untruthful goal if by doing so they can get a better outcome. The focus is on three majoritarian voting rules which are found to be manipulable. Therefore, we study restrictions on both the language of the goals and on the strategies allowed to the agents to discover islands of strategy-proofness. We also present a game-theoretic extension of a recent model of opinion diffusion over networks of influence. In the influence games defined here, agents hold goals expressed as formulas of LTL and they can choose whether to use their influence power to make sure that their goal is satisfied. Classical solution concepts such as weak dominance and winning strategy are studied for influence games, in relation to the structure of the network and the goals of the agents. Finally, we introduce a novel class of concurrent game structures (CGS) in which agents can have shared control over a set of propositional variables. Such structures are used for the interpretation of formulas of alternating-time temporal logic, thanks to which we can express the existence of a winning strategy for an agent in a repeated game (as, for instance, the influence games mentioned above). The main result shows by means of a clever construction that a CGS with shared control can be represented as a CGS with exclusive control. In conclusion, this thesis provides a valuable contribution to the field of collective decision-making by introducing a novel framework of voting based on individual propositional goals, it studies for the first time the aggregation of generalized CP-nets, it extends a framework of opinion diffusion by modelling rational agents who use their influence power as they see fit, and it provides a reduction of shared to exclusive control in CGS for the interpretation of logics of strategic reasoning. By using different logical languages, agents can thus express their goals and preferences over the decision to be taken, and desirable properties of the decision process can be ensured

Group reasoning in social environments

While modeling group decision making scenarios, the existence of a central authority is often assumed which is in charge of amalgamating the preferences of a given set of agents with the aim of computing a socially desirable outcome, for instance, maximizing the utilitarian or the egalitarian social welfare. Departing from this classical perspective and inspired by the growing body of literature on opinion formation and diffusion, a setting for group decision making is studied where agents are selfishly interested and where each of them can adopt her own decision without a central coordination, hence possibly disagreeing with the decision taken by some of the other agents. In particular, it is assumed that agents belong to a social environment and that their preferences on the available alternatives can be influenced by the number of “neighbors” agree- ing/disagreeing with them. The setting is formalized and studied by modeling agents’ reasoning capabilities in terms of weighted propositional logics and by focusing on Nash-stable solutions as the prototypical solution concept. In particular, a thoroughly computational complexity analysis is conducted on the problem of deciding the existence of such stable outcomes. Moreover, for the classes of environments where stability is always guaranteed, the convergence of Nash dynamics consisting of sequences of best response updates is studied, too

Convergence of Opinion Diffusion is PSPACE-complete

We analyse opinion diffusion in social networks, where a finite set of individuals is connected in a directed graph and each simultaneously changes their opinion to that of the majority of their influencers. We study the algorithmic properties of the fixed-point behaviour of such networks, showing that the problem of establishing whether individuals converge to stable opinions is PSPACE-complete

Consumer innovativeness: a marketing approach

By innovativeness we mean the predisposition of a consumer to adopt a product earlier than most others. Various studies have shown that across product categories, innovators tend to be: opinion leaders, risk takers, more likely to obtain information from mass media than through word of mouth, open to new ideas and change, relatively young etc. Marketers want to identify the segment of the market that is most likely to adopt a new product when it is the first introduced. This article describes we ask some key questions about the nature of innovativeness and try to make a correlation between characteristics of the innovators and innovativeness.innovativeness, new product, opinion leaders, risk takers.

Opinion Leaders in Real Estate Markets

The purpose of this research paper is to examine the influence of opinion leaders in real estate markets. First, we provide a literature review of opinion leaders and real estate markets in India. Secondly, the variables that influence the opinion leaders are established and their measurement is well defined. Thirdly, a survey has been conducted by using a self-administered questionnaire, which was sent to 234 individuals who are responsible for handling real estate firms. The research model is empirically tested in a sample of 128 respondents by using a chi-square analysis. This study finds that opinion leaders in real estate markets possess significantly higher levels in exposure to media sources, social involvement, product knowledge, innovativeness, and computer usage than non-leaders. Opinion leaders also possess a higher degree of social networking and have used the internet more frequently for longer sessions than non-leaders. Finally, we identify the key implications, conclude the research finding and explore potential avenues for future research.Financial leverage; Asset valuation; Taxation

Regional science at the turn of the century: Reflections on its epistemological status

As a contribution to the current debate on the state-of-the art of regional science, this paper presents some reflections on the epistemological and methodological status of the discipline as we approach the turn of the century. First of all, and contrary to the widely held view that quantitative approach is seriously 'in crisis', it is argued that the discipline is going through a period of intensive, but constructive, theoretical development. To support this assertion, the authors suggest that it is important to abandon a hidden source of prejudice: the tendency to evaluate the present situation in terms of an outdated conception of the discipline. Modern quantitative geography and regional science is a vast and varied scientific field, which has radically evolved under the pressure of changing theoretical paradigms and technological advance. It has little to do with the old regional science of the 60s. The first part of the paper reviews this evolution: 1. from the original goal of applying to geography the tools of classical science, such as statistics, optimization and modelling (whose use was made possible in the 60s by the availability of the new "number crunching" computers) 2. to the present informatization (and hence quantification) of all branches of regional science, based on PCs and the Net, used as tools not just for computation, but for data handling, representation, visualization and communication). An attempt is made to fit all of these efforts, those with a long tradition (modelling, O.R., gaming simulation, statistics etc.), as well as the more recent approaches (expert systems, G.I.S., hypermedia, virtual reality, A.I.) into a single framework, stressing the specific aims of each and identifying existing - or potential - interconnections. In the second part of the paper we focus on the new frontiers of regional science and quantitative geography with particular reference to the processes of analysis and planning. It is suggested that: 1. the goal of analysis is shifting from simulation (the explicitation in terms of the "scientific method") of the mental processes involved in problem-solving, to the replication of the human ability to "formulate problems". This implies that creativity, and related aspects such as learning, and expertise, will come increasingly within the scope of research in regional science 2. progress in planning will be limited unless we will be able to go beyond the misleading counterposition between the formalised "rational" approach and the intuitive design approach. A fruitful way to cope with planning in a complex world is to integrate the two strategies and, in doing so, to tap into wider sources of knowledge. In other words, it is important to learn the 'art' of using the tools of geographical science.