YouTube is the second largest social media platform in the world, with a multitude of popularchannels which combine politicised commentary with news reporting. The platform providesdirect accessibility to data which makes it possible for the commentators to adjust theircontent to reach wider audiences, however done to an extreme could mean that the creatorspick topics which are the most financially beneficial or lead to fame. If this were the case itwould highlight populist newsmaking and the mechanisms behind it. To investigate theproduction-consumption interaction, data from the 10 most popular channels for 2021 wascollected. Using latent Dirichlet allocation and preferential attachment analysis, the effect ofcumulative advantage, and whether topic choice was driven by views were measured. Apositive feedback loop, where prevalent topics become more prevalent, was found in all buttwo channels, but picking topics which generated more views was only present for onechannel. The findings imply that the top political news commentators over a year have a set oftopics which they return to at a high degree, but choosing the topics which simply are themost popular for the time is not a general feature.

This dissertation is a collection of five essays examining different aspects of consumer and firm behavior in dynamic markets. The first essay combines clickstreams of users at a major news website with Facebook activity data, to study if social networks complement or compete for online browsing time. This is the first empirical study to show that Facebook activity increases time spent on news sites. Online news consumption is a shared experience, as the activity of social network friends strongly influences the behavior of other network members. We also find that visitors’ own browsing patterns are important predictors of online content consumption. The second essay examines consumer attitudes to risk and uncertainty vis-a-vis their purchase and search decisions for air tickets online. Using a two-stage model of purchase incidence and carrier choice, we find that browsing experience, search costs and product characteristics are important predictors of purchase incidence. Implications for website managers are also discussed. The third essay provides insights on the impact of customer heterogeneity and preference stochasticity on behavior based price discrimination. While customer heterogeneity intensifies competition, resulting in greater price discrimination, preference stochasticity reduces the incidence of price discrimination. Overall, the effect of preference stochasticity is more salient. The fourth essay presents models of strategic interaction to analyze the impact of dominance and concentration on pricing strategies. We show that lack of market dominance is a sufficient condition for discounts to existing customers. We further test our predictions via an experiment with pricing professionals. The behavior of professionals confirms that price discrimination increases with market dominance and concentration; however, lack of dominance is not a sufficient condition for loyalty discounts. We contend that increasing competition is a more effective means of improving consumer welfare compared to regulating dominant firms. The fifth essay considers the role of identity and customer type recognition in influencing pricing behavior in dynamic markets with symmetric and asymmetric players. When customer identity is detectable firms charge higher prices to repeat customers while new customers are offered lower prices. However, pricing behavior changes when information on customer type is available and this behavior varies with market structure. Age, education and experience of managers are also found to significantly influence pricing behavior.

! ! Abstract This thesis explores and analyses influence of smartphones, tablets and e-readers launch on today's media development both from publisher's and media consumer's view. Main goal of this work is to map turbulent media evolution thanks possibilities, brought by revolutionary devices especially iPhone and iPad and their impact on publishing houses and traditional media. The thesis envisages the future of printed media and its co-existing together with the digital versions of traditional titles, possibilities and consumer willingness to pay for the digital content and specifics of the copyright in the digital media world. Least but not last thesis tries to discover individual target groups of each media including their typical behavior and arguing over the diversion from the traditional media towards the digital media.

! ! Abstract This thesis explores and analyses influence of smartphones, tablets and e-readers launch on today's media development both from publisher's and media consumer's view. Main goal of this work is to map turbulent media evolution thanks possibilities, brought by revolutionary devices especially iPhone and iPad and their impact on publishing houses and traditional media. The thesis envisages the future of printed media and its co-existing together with the digital versions of traditional titles, possibilities and consumer willingness to pay for the digital content and specifics of the copyright in the digital media world. Least but not last thesis tries to discover individual target groups of each media including their typical behavior and arguing over the diversion from the traditional media towards the digital media.

Les services Internet populaires modèlent et remodèlent fondamentalement les moyens traditionnels de communication des personnes, ayant ainsi un impact majeur sur leur vie sociale. Deux des services Internet très populaires avec cette caractéristique sont les Réseaux sociaux en ligne (OSN) et les systèmes Peer-to-Peer (P2P). Les ONS fournissent un environnement virtuel où les gens peuvent partager leurs informations et leurs intérêts tout en étant en contact avec d'autres personnes. D'autre part, les systèmes P2P, qui sont toujours l'un des services populaires avec une grande proportion de l'ensemble du trafic Internet, offrent une occasion en or pour leurs clients de partager un type de contenu différent, y compris le contenu protégé. En dehors de l'énorme popularité des ONS et des systèmes de P2P parmi les utilisateurs réguliers, ils sont intensivement utilisés par les professionnels (grandes entreprises, politiciens, athlètes, célébrités en cas d'ONS et éditeurs de contenu professionnels en cas de P2P) afin d'interagir avec les gens à des fins différentes (campagnes marketing, les commentaires des clients, amélioration de la réputation publique, etc.) Dans cette thèse, nous caractérisons le comportement des utilisateurs réguliers et professionnels dans les deux services mentionnés populaires (ONS et P2P) en termes de stratégies de publication, de consommation de contenu et d'analyse comportementale. À cette fin, cinq de nos études menées sont présentées dans ce manuscrit comme suit: - "L'évolution des contenus multimédias", qui présente une analyse approfondie sur l'évolution du contenu multimédia disponible en BitTorrent en se concentrant sur quatre mesures pertinentes à travers différentes catégories de contenu : la disponibilité du contenu, la popularité du contenu, la taille de contenu et les commentaires de l'utilisateur - "La réaction des utilisateurs professionnels face aux actions de lutte contre le piratage", en examinant l'impact de deux grandes actions de lutte contre le piratage - la fermeture de Megaupload et la mise en œuvre de la loi anti-piratage française (HADOPI) - sur le comportement des publicateurs professionnels dans le plus grand portail de BitTorrent qui sont les principaux fournisseurs de contenu en ligne protégé. - "La quantité d'informations divulguées sur Facebook", en enquêtant sur l'exposition publique des profils utilisateurs, une grande base de données comprenant un demi-million d'utilisateurs réguliers. - "Les utilisateurs professionnels Cross Posting Activity», en analysant le modèle de publication des utilisateurs professionnels de mêmes informations sur trois grands ONS à savoir Facebook, Google+ et Twitter. - "Les stratégies des utilisateurs professionnels dans les ONS", où nous étudions la stratégie globale d'utilisateurs professionnels par secteur (par exemple, les entreprises de voitures, l'habillement, politiques, etc.) sur Facebook, Google+ et Twitter. Les résultats de cette thèse fournissent une vision d'ensemble pour comprendre certains aspects comportementaux importants de différents types d'utilisateurs des services Internet populaires et ces contributions peuvent être utilisées dans divers domaines (par exemple analyse de campagne marketing et publicité, etc.) et les différentes parties peuvent bénéficier des résultats et des méthodologies mises en œuvre telles que les FAI et les propriétaires des services pour leur planification ou l'expansion des services actuels à venir, ainsi que les professionnels pour accroître leur succès sur les médias sociaux / Popular Internet services are fundamentally shaping and reshaping traditional ways of people communication, thus having a major impact on their social life. Two of the very popular Internet services with this characteristic are Online Social Networks (OSNs) and Peer-to-Peer (P2P) systems. OSNs provide a virtual environment where people can share their information and interests as well as being in contact with other people. On the other hand, P2P systems, which are still one of the popular services with a large proportion of the whole Internet traffic, provide a golden opportunity for their customers to share different type of content including copyrighted content. Apart from the huge popularity of OSNs and P2P systems among regular users, they are being intensively used by professional players (big companies, politician, athletes, celebrities in case of OSNs and professional content publishers in case of P2P) in order to interact with people for different purposes (marketing campaigns, customer feedback, public reputation improvement, etc.). In this thesis, we characterize the behavior of regular and professional users in the two mentioned popular services (OSNs and P2P systems) in terms of publishing strategies, content consumption and behavioral analysis. To this end, five of our conducted studies are presented in this manuscript as follows: - “The evolution of multimedia contents", which presents a thorough analysis on the evolution of multimedia content available in BitTorrent by focusing on four relevant metrics across different content categories: content availability, content popularity, content size and user's feedback. - “The reaction of professional users to antipiracy actions", by examining the impact of two major antipiracy actions, the closure of Megaupload and the implementation of the French antipiracy law (HADOPI), on professional publishers behavior in the largest BitTorrent portal who are major providers of online copyrighted content. - “The amount of disclosed information on Facebook", by investigating the public exposure of Facebook users' profile attributes in a large dataset including half million regular users. - “Professional users Cross Posting Activity", by analyzing the publishing pattern of professional users which includes same information over three major OSNs namely Facebook, Google+ and Twitter. - “Professional Users' Strategies in OSNs", where we investigate the global strategy of professional users by sector (e.g., Cars companies, Clothing companies, Politician, etc.) over Facebook, Google+ and Twitter. The outcomes of this thesis provide an overall vision to understand some important behavioral aspects of different types of users on popular Internet services and these contributions can be used in various domains (e.g. marketing analysis and advertising campaign, etc.) and different parties can benefit from the results and the implemented methodologies such as ISPs and owners of the Services for their future planning or expansion of the current services as well as professional players to increase their success on social media