Revisiting Opinion Dynamics with Varying Susceptibility to Persuasion via Non-Convex Local Search

International audienceWe revisit the opinion susceptibility problem that was proposed by Abebe et al. [1], in which agents influence one another's opinions through an iterative process. Each agent has some fixed innate opinion. In each step, the opinion of an agent is updated to some convex combination between its innate opinion and the weighted average of its neighbors' opinions in the previous step. The resistance of an agent measures the importance it places on its innate opinion in the above convex combination. Under non-trivial conditions, this iterative process converges to some equilibrium opinion vector. For the unbudgeted variant of the problem, the goal is to select the resistance of each agent (from some given range) such that the sum of the equilibrium opinions is minimized. Contrary to the claim in the aforementioned KDD 2018 paper, the objective function is in general non-convex. Hence, formulating the problem as a convex program might have potential correctness issues. We instead analyze the structure of the objective function, and show that any local optimum is also a global optimum, which is somehow surprising as the objective function might not be convex. Furthermore, we combine the iterative process and the local search paradigm to design very efficient algorithms that can solve the unbudgeted variant of the problem optimally on large-scale graphs containing millions of nodes

Opinion dynamics optimization by varying susceptibility

A long line of work in social psychology has studied variations in people’s susceptibility to persuasion—the extent to which they are willing to modify their opinions on a topic. This body of literature suggests an interesting perspective on theoretical models of opinion formation by interacting parties in a network: in addition to considering interventions that directly modify people’s intrinsic opinions, it is also natural to consider interventions that modify people’s susceptibility to persuasion. In this work, motivated by this fact, we propose an influence optimization problem. Specifically, we adopt a popular model for social opinion dynamics, where each agent has some fixed innate opinion, and a resistance that measures the importance it places on its innate opinion; agents influence one another’s opinions through an iterative process. Under certain conditions, this iterative process converges to some equilibrium opinion vector. For the unbudgeted variant of the problem, the goal is to modify the resistance of any number of agents (within some given range) such that the sum of the equilibrium opinions is minimized; for the budgeted variant, in addition the algorithm is given upfront a restriction on the number of agents whose resistance may be modified. We prove that the objective function is in general non-convex. Hence, formulating the problem as a convex program as in an early version of this work (Abebe et al., KDD’18) might have potential correctness issues. We instead analyze the structure of the objective function, and show that any local optimum is also a global optimum, which is somehow surprising as the objective function might not be convex. Furthermore, we combine the iterative process and the local search paradigm to design very efficient algorithms that can solve the unbudgeted variant of the problem optimally on large-scale graphs containing millions of nodes. Finally, we propose and evaluate experimentally a family of heuristics for the budgeted variant of the problem.Accepted manuscrip

Exploring human factors issues & possible countermeasures in password authentication

PhD ThesisThis thesis is concerned with usable security. It describes a series of experiments to understand users’ behaviour in the domain of password authentication. The thesis is comprised of two parts. Part 1 reports on experiments into how different persuasion strategies can be used to increase the strength of users’ password. Existing research indicates that the lack of persuasive elements in password guidelines may lead to a lack of motivation to produce strong passwords. Thus, an experimental study involving seventy-five participants was conducted to evaluate the effectiveness of a range of persuasion strategies on password strength. In addition this experiment explores how personality variables affect the susceptibility of users to persuasion. The results showed that passwords created by users who received password guidelines that include a persuasion strategy produce stronger passwords than a control group. In terms of the personality variables, the result shows that there are certain personality types that tend to produce slightly better passwords than others; but it is difficult to draw a firm conclusion about how personality affects susceptibility to persuasion. The second part of this thesis presents an innovative alternative to text-based passwords, namely, graphical password schemes. Graphical passwords take advantage of the superior ability of humans to remember graphics and pictures over text and numbers. Research shows that graphical password schemes are a promising alternative, but that they are susceptible to shoulder surfing attacks, resulting in scepticism about adoption. Thus in part 2 of the thesis, three innovative shoulder surfing defence techniques are proposed and implemented in a small-scale prototype with a specific focus given to one type of graphical password; The Draw-A-Secret (DAS) scheme. The results of two separate experimental studies involving sixty-five and thirty participants respectively to evaluate the proposed defence techniques from the perspectives of security and usability are presented. The results show that the technique which, on theoretical grounds, was expected to be quite effective, provides little protection. A second technique which did provide the best overall shoulder surfing defence; created usability problems. But a third technique provided a reasonable shoulder surfing defence and good usability simultaneously; a good balance which the other two techniques did not achieve. The proposed defence techniques and experimental results are directly relevant to other graphical password schemes of the same category with slight modification to suit the requirements of the scheme intended. In summary, the thesis contributes to the discussion of some key usability problems which exist around password authentication domains. All the proposed countermeasures are evaluated through a series of experimental studies which present several intriguing discussions and promising findings

Disseny d'un model d'avaluació de resultats de l'activitat de màrqueting per a empreses competint al mercat català i amb relació contractual amb els seus clients

L’objectiu de la tesi doctoral és el de desenvolupar un model que permeti valorar de forma objectiva les actuacions en matèria de màrqueting portades a terme per una organització. Aquest model està constituït per un conjunt de variables descriptives i quantitatives, anomenades variables de control, juntament amb una metodologia de càlcul i un sistema d’indicadors integrat que facilita la traçabilitat de les inversions de màrqueting i explicita la relació causa-efecte entre aquestes i el valor generat per a l’organització. El model s’utilitza per a valorar dades reals d’organitzacions que operin al mercat català i que compleixin la condició de basar la relació amb els seus clients en un model contractual (com veurem més endavant, és inviable aplicar un model comú per a tot tipus d’empresa). L’objectiu, doncs, és la valoració de l’acompliment dels seus objectius en relació als seus actius de mercat (marca i valor de client) i la creació d’un model específic, no generalitzable, per a aquest tipus d’empreses. Un segon objectiu d’aquest treball és l’anàlisi de les principals publicacions especialitzades referents des d’un punt de vista global i local, proposant en primer lloc una terminologia clara en relació a l’activitat de màrqueting, l’acompliment dels seus objectius i la conceptualització d’actius de mercat, i analitzant, en segon, l’impacte d’aquests àmbits i la seva evolució en els últims quinze anys. Alguns estudis previs (Llonch et al., 2002; Ambler i Xiucun, 2003; entre d’altres) es centren a comparar empreses per sectors, funcionalitats i països. És probable, com apunta Llonch et al. (2002) al fer això, que casuístiques atribuïbles a diferències geogràfiques i nacionals es tractin erròniament com a empresarials. A tal efecte, aquest estudi elimina la variabilitat per país i sector (parcialment, aquest darrer), proposant un model acotat, tal com recomanen Ambler et al., (2001), Llonch et al (2002), entre d’altres, que pugui servir de referència en la metodologia i en la validesa conceptual, i no tant en els resultats del model en un context més genèric. Pauwels (2009) demostra la relació entre la creació d’un model predefinit de variables i la millora del càlcul de l’eficiència en la despesa en màrqueting, pel que la creació d’aquest model integrat té l’objectiu d’esdevenir una eina de Gestió del Rendiment Corporatiu (GRC, en endavant1) (Bauer, 2004) aplicada a la gestió de màrqueting i els seus actius. Aquesta particularització del GRC rep el nom de Gestió del Rendiment de Màrqueting (GRM, en endavant2) (Ambler, 2000) i el seu objectiu és el d’augmentar la usabilitat i faciliti la generació d’informació per a la presa de decisions de la línia directiva de les organitzacions. L’abast de la tesi és el de crear el model des d’una perspectiva d’avaluació de l’activitat de màrqueting per part de la línia directiva, i no pas el desenvolupament informàtic d’una eina de suport a la presa de decisions ja que això, com apunten diversos autors (Dover, 2004; Schiff, 2008) i es tractarà amb més profunditat en el capítol 5, implicaria un nivell de personalització per cada empresa que no és objectiu d’aquesta tesi.The thes is aims to develop a practical model to asses m arketing perform ance within an organization. The model is basically structured around control metrics both from a qualitative and quantitatve approach, together with an integrated system of key performance indicators that enables marketing accountability through different organisational divisions, thus stating a solid cause/effect relationship between marketing activities and the value created for the organisation. The aformentioned model is used to assess marketing activites for catalan com panies with a contract-based customer relationship. Final assessment includes also a dynamic valuation of the company's market as sets . A second objective of the thes is is to review the current state of the art of marketing assessment literature from specialized journals both from a global and a local pers pective, defining a comprehensive list of related terms about marketing performance measurement, market-asset description and valuation and an accurate analysis about its evolution throughout the last 15 years.Postprint (published version

Untangling hotel industry’s inefficiency: An SFA approach applied to a renowned Portuguese hotel chain

The present paper explores the technical efficiency of four hotels from Teixeira Duarte Group - a renowned Portuguese hotel chain. An efficiency ranking is established from these four hotel units located in Portugal using Stochastic Frontier Analysis. This methodology allows to discriminate between measurement error and systematic inefficiencies in the estimation process enabling to investigate the main inefficiency causes. Several suggestions concerning efficiency improvement are undertaken for each hotel studied.info:eu-repo/semantics/publishedVersio