Dans l'entreprise, un certain nombre de risques sont mal cernés et non assurés. Ce sont par exemple les contrefaçons, les fraudes mais également les campagnes de désinformation qui peuvent déstabiliser durablement l'entreprise. On essayera dans la thèse de définir les manipulations : désinformation, propagande, rumeur, d'abord en référence à l'Histoire, puis en examinant un certain nombre d'exemples tirés des domaines militaires et diplomatiques. A partir du XIXème siècle, l'économie entre en jeu et les mêmes campagnes de désinformation touchent alors  l'entreprise. On examinera alors au travers de divers exemples puisés dans l'actualité récente les méthodes employées pour toucher un marché. A partir des cette analyse on tentera de mettre en place une méthode de prévention. Se tournant vers les cindyniques ou sciences du danger dont les modèles et hyperespace sont utilisés au quotidien dans l'industrie pour prévenir les accidents, on tentera de voir si ces concepts peuvent être utilisés dans une prévention des manipulations. / In the industry, a lot of risks are unknown or not insured. Among them are, for example, counterfeiting, fraud, but also manipulation of information, which can destabilize firms for a long time. In this work, we shall try to define what is disinformation, propaganda, rumor, first by looking at historical references, and then by analyzing examples taken from military and diplomatic fields. In the 19th century, as economy becomes a major factor, one starts seeing disinformation campaigns being launched against firms. We shall examine through recent examples different methods used to rig a market. Based on this analysis we shall attempt to find ways and means to prevent these types of dangers. Finally, we shall investigate how the models and hyperspace concepts of the new science of risks (or cindynics), frequently used by the industry to prevent accidents, can be used in the prevention of disinformation.

The first part of the thesis gives a systematic overview and conceptual analysis of the literature on studying misinformation and disinformation in social media, with a special focus on research projects using large scale data obtained from Twitter and Facebook. The literature review gives a detailed overview of the scope of data collected by the various research projects; the means of accessing the data, which are rooted in the concrete socio-technical arrangement of the various platforms, and the type of analytical tools they apply. Furthermore, it also maps the various theoretical questions behind the research projects. The author of the thesis also gives his own definition of information manipulation and describes a conceptual model of information manipulation in the context of social media. The second part of the thesis applies some of the insights from the literature review to a large Twitter data set collected during the monitoring of African elections. The analysis follows a qualitative approach and focuses on case studies created from specific incidents during the elections. Each of these incidents illustrates a special aspect of the problem of information manipulation in online social media.

The advent of information services introduces many advantages, for example, in trade, production and services. While making important descisons today, people increasingly rely on the information gleaned from such services. Presumably, as such, information from these services has become a target of manipulation. During the past decade, we have already observed many forms of information manipulation that misrepresents or alters reality. Some popular manipulation -- we have ever witnessed on the Internet -- include using black hat SEO techniques to drive up the ranking of a disreputable business, creating disinformative campaigns to conceal political dissidence, and employing less-than-honest product assessments to paint a rosy picture for inferior wares. Today, emerging web services and technologies greatly facilitated and enhanced people's lives. However, these innovations also enrich the arsenal of manipulators. The sheer amount of online information available today can threaten to overwhelm any user. To help ensure that users do not drown in the flood of information, modern web services are increasing relying upon personalization to improve the quality of their customers' experience. At the same time, personalization also represents new ammunition for all manipulators seeking to steer user eyeballs, regardless of their intents. In this thesis, I demonstrate a new unforeseen manipulation that exploits the mechanisms and algorithms underlying personalization. To undermine the effect of such manipulation, this thesis also introduces two effective, efficient mitigation strategies that can be applied to a number of personalization services. In addition to aforementioned personalization, increasingly prevalent browser extensions augment the ability to distort online information. In this thesis, I unveil an overlooked but widespread manipulation phenomenon in which miscreants abuse the privilege of browser extensions to tamper with the online advertisement presented to users. Considering that online advertising business is one of the primary approaches used to monetize free online services and applications available to users, and reckless ad manipulation may significantly roil advertising ecosystem, this thesis scrutinizes the potential effect of ad manipulation, and develops a technical approach to detect those browser extensions that falsify the ads presented to end users. Although the thesis merely discusses several manipulation examples in the context of the Internet, the findings and technologies presented in this thesis introduce broad impacts. First, my research findings raise Internet users' awareness about pervasive information manipulation. Second, the proposed technologies help users alleviate the pernicious effects of existing information manipulation. Finally, accompanying the findings and technologies is publicly available open-source software and tools that will help an increasing number of users battle against the growing threat of information manipulation.

Starting from 2005 the disclosure of financial forecast for Taiwanese public companies has not been mandatory, firms can decide whether they want to disclose, and if so, how and when to disclose. How does the investor's reaction affect this decision? Furthermore, what is the trade-off between transparency and precision? This study develops a theoretical model in which the voluntary disclosure of earnings forecast is a double-edged sword. Such disclosure may reduce information asymmetry, but simultaneously allows entrepreneurs to hype the stock. The proposed model assumes that insiders might manipulate information and investors can learn with bounded rationality. The analytical results demonstrate that entrepreneurs may forgo earnings forecast disclosure if they can achieve greater profit under non-disclosure. In the multiperiod case, this study shows that insiders would reduce their forecast manipulation behavior due to the cost of forecast error and diminishing marginal expected profit. This study accommodates an explanation of the decrease in voluntary disclosure and the popularity of investor conferences in Taiwan. The inferences of the proposed model are examined based on forecasts issued by Taiwanese listed firms. The empirical results evidence a positive relationship between insiders¡¦ trading profit and manipulation of earnings forecast. Additionally, insiders¡¦ trading profit regarding forecast revisions is greater under voluntary disclosure than mandatory disclosure. This study offers important insights into earnings forecast policy in emerging markets.

Online product reviews have become an important and influential source of information for consumers. Firms often manipulate online product reviews to influence consumer perceptions about the product, making it a research topic of urgent need for theory development and empirical investigation. In this thesis, we examine how consumers perceive and respond to the three commonly used manipulation tactics. Firstly, an exploratory pre-study via in-depth interviews with online shoppers indicates that consumers commonly have the knowledge for online review manipulations as well as for detecting them. In the first study, a survey was used to investigate the three popular manipulation tactics in terms of ethicality and deceptiveness. They rated hiding/deleting unfavorable messages as the most deceptive and unethical, followed by anonymously adding positive messages, and then offering incentives for posting favorable messages. In study 2, in a simulated field experiment, we introduce persuasion knowledge to further examine the negative influence of review manipulations on consumers’ attitudes. The results suggest that review manipulation increases suspicion of manipulations but can hardly reduce purchase intention of focal products. We also find that consumers’ persuasion knowledge enhances suspicion of manipulation, but lessens the negative impact of suspicion on purchase intention. The third study uses secondary data of a branded e-retailer and its third party website to cross-validate the effect of manipulations on product sales. The results confirm our hypotheses that review manipulation are effective in promoting sales; however, this influence would decrease over time. This research contributes to the online marketing literature by augmenting the Information Manipulation Theory and Persuasion Knowledge Model to examine the deceptive persuasion in the online context and its impact on consumer behavior. Furthermore, we also contribute to the literature of online WOM by empirically examining the influence of review manipulations on sales. Our findings provide valuable insights to practitioners and policy makers on the pitfalls of online manipulation activities and the need to ensure the healthy development of e-commerce.

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This thesis consists of three essays in the field of information economics. The first essay studies manipulation of information by partisan media. The recent increase in partisan media has generated interest in what drives media outlets to become more partisan. I develop a model to study the role of diffusion of information by word of mouth. In the model, a media outlet designs an information policy, which specifies the level of partisan slant in the outlet’s news reports. The news spread via a communication chain in a population of agents with heterogeneous preferences. The slant has an impact on whether the agents find the news credible and on their incentives to pass the news to others. The analysis elucidates how partisanship of media can be driven by political polarisation of the public and by the tendency of people to interact with people with similar political views. The second essay, co-authored by Jakub Redlicki, investigates falsification of scientific evidence by interest groups. We analyse a game between a biased sender (an interest group) and a decision maker (a policy maker) where the former can falsify scientific evidence at a cost. The sender observes scientific evidence and knows that it will also be observed by the decision maker unless he falsifies it. If he falsifies, then there is a chance that the decision maker observes the falsified evidence rather than the true scientific evidence. First, we investigate the decision maker’s incentives to privately acquire independent evidence, which not only provides additional information to her but can also strengthen or weaken the sender’s falsification effort. Second, we analyse the decision maker’s incentives to acquire information from the sender. The third essay analyses competition between interest groups for access to a policy maker. I study a model of lobbying in which two privately-informed experts (e.g., interest groups) with opposite goals compete for the opportunity to communicate with a policy maker. The main objective is to analyse the benefits which competition for access brings to the policy maker as opposed to hiring an expert in advance. I show that competition for access is advantageous in that it provides the policy maker with some information about the expert who did not gain access and gives the experts an incentive to invest in their communication skills. On the other hand, hiring an expert in advance allows the policy maker to use a monetary reward to incentivise the expert to invest more in his communication skills.

A presente pesquisa investiga os impactos da regulação econômica nas escolhas de práticas contábeis. Buscando identificar a relação existente, são apresentadas pesquisas em gerenciamento da informação contábil (de resultado e do balanço patrimonial) e as teorias econômicas da regulação. Em seguida, são apresentadas as evidências empíricas de como a regulação econômica incentiva a adoção de determinadas práticas contábeis. Nesse mister, é apresentada a regulação financeira exercida pela Agência Nacional de Saúde Suplementar (ANS) sobre as entidades operadoras de planos de assistência à saúde (OPS), também chamadas de planos de saúde. Essa regulação financeira consiste no acompanhamento, pela ANS, da situação econômico-financeira das OPS. A ANS compara os índices calculados a partir das informações contábeis recebidas, eletronicamente, das OPS, com parâmetros estabelecidos a priori. Se determinada OPS não atender, satisfatoriamente, os parâmetros, fica sujeita ao afastamento de seus administradores de suas funções e até à liquidação de seus ativos. Por fim, as teorias da regulação e do gerenciamento da informação contábil são revisitadas à luz da Nova Economia Institucional, identificando-se, portanto, a Contabilidade como parte integrante de um contrato (regulação) cujos custos são diferentes de zero (custos de transação), de forma que a informação contábil é a cola que mantém a firma unida e a regulação financeira em atividade. / This study analyzes how the economic regulation impacts on accounting policy choices. With a view to identifying the existing relationship between both, the economic theories of regulation and research on earnings and balance sheet management are discussed. Then, empirical evidence is presented of how economic regulation stimulates the choice of certain accounting policies, related to the Brazilian Health Care Agencys (ANS) equivalent to the US Federal governments Office of Health Maintenance Organizations financial regulation of health maintenance organizations (HMO), called OPS in Brazil. OPS have their economic-financial situation monitored by the ANS, which compares the indices calculated on the basis of electronically received financial information with some previously established financial thresholds. If these are not complied with to a reasonable extent, this may lead to the HMOs liquidation. Finally, the regulation and earnings and balance sheet management theories are discussed under the lens of New Institutional Economics, which sees Accounting as part of a contract (regulation), whose costs are positive (transaction costs), and accounting information as the glue that keeps the firm together and keeps the financial regulation working.

A presente pesquisa investiga os impactos da regulação econômica nas escolhas de práticas contábeis. Buscando identificar a relação existente, são apresentadas pesquisas em gerenciamento da informação contábil (de resultado e do balanço patrimonial) e as teorias econômicas da regulação. Em seguida, são apresentadas as evidências empíricas de como a regulação econômica incentiva a adoção de determinadas práticas contábeis. Nesse mister, é apresentada a regulação financeira exercida pela Agência Nacional de Saúde Suplementar (ANS) sobre as entidades operadoras de planos de assistência à saúde (OPS), também chamadas de planos de saúde. Essa regulação financeira consiste no acompanhamento, pela ANS, da situação econômico-financeira das OPS. A ANS compara os índices calculados a partir das informações contábeis recebidas, eletronicamente, das OPS, com parâmetros estabelecidos a priori. Se determinada OPS não atender, satisfatoriamente, os parâmetros, fica sujeita ao afastamento de seus administradores de suas funções e até à liquidação de seus ativos. Por fim, as teorias da regulação e do gerenciamento da informação contábil são revisitadas à luz da Nova Economia Institucional, identificando-se, portanto, a Contabilidade como parte integrante de um contrato (regulação) cujos custos são diferentes de zero (custos de transação), de forma que a informação contábil é a cola que mantém a firma unida e a regulação financeira em atividade. / This study analyzes how the economic regulation impacts on accounting policy choices. With a view to identifying the existing relationship between both, the economic theories of regulation and research on earnings and balance sheet management are discussed. Then, empirical evidence is presented of how economic regulation stimulates the choice of certain accounting policies, related to the Brazilian Health Care Agencys (ANS) equivalent to the US Federal governments Office of Health Maintenance Organizations financial regulation of health maintenance organizations (HMO), called OPS in Brazil. OPS have their economic-financial situation monitored by the ANS, which compares the indices calculated on the basis of electronically received financial information with some previously established financial thresholds. If these are not complied with to a reasonable extent, this may lead to the HMOs liquidation. Finally, the regulation and earnings and balance sheet management theories are discussed under the lens of New Institutional Economics, which sees Accounting as part of a contract (regulation), whose costs are positive (transaction costs), and accounting information as the glue that keeps the firm together and keeps the financial regulation working.