Spillovers in networks of user generated content : evidence from 23 natural experiments on Wikipedia

Endogeneity in network formation hinders the identification of the role that social networks play in generating spillovers, peer effects and other externalities. This paper tackles this problem and investigates how the link network between articles on the German Wikipedia influences the attention and content generation individual articles receive. Identification exploits local exogenous shocks on a small number of nodes in the network. It can thus avoid the usually required, but strong, assumptions of exogenous observed characteristics and link structure in networks. Exogenous variation is generated by natural and technical disasters or by articles being featured on the German Wikipedia’s start page. The effects on neighboring pages are substantial; I observe an increase of almost 100 percent in terms of both views and content generation. The aggregate effect over all neighbors is also large: I find that a view on a treated article converts one for one into a view on a neighboring article. However, the resulting content generation is small in absolute terms. My approach also applies if, due to a lack of network data, identification through partial overlaps in the network structure fails (e.g. in classrooms). It helps bridge the gap between the experimental and social network literatures on peer effects

99 cent: Price points in e-commerce

Basu (2006) argues that the prevalence of 99 cent prices in shops can be explained with rational consumers who disregard the rightmost digits of the price. This bounded rational behaviour leads to a Bertrand equilibrium with positive markups. We use data from an Austrian price comparison site and find results highly compatible with Basu's theory. We can show that price points - in particular prices ending in 9 - are prevalent and have significant impact on consumer demand. Moreover, these price points are sticky; neither the price-setter itself wants to change them neither the rivals do underbid these prices, if they represent the cheapest price on the market. --Competitive Behaviour,Pricing Behaviour,E-Commerce,Pricing in the Nines,Focal Pricing

99 cent: Price Points in E-Commerce

Basu (2006) argues that the prevalence of 99 cent prices in shops can be explained with rational consumers who disregard the rightmost digits of the price. This bounded rational behaviour leads to a Bertrand equi- librium with positive markups. We use data from an Austrian price com- parison site and find results highly compatible with Basu's theory. We can show that price points - in particular prices ending in 9 - are preva- lent and have significant impact on consumer demand. Moreover, these price points are sticky; neither the price-setter itself wants to change them neither the rivals do underbid these prices, if they represent the cheapest price on the market.e-commerce, price comparison, price policy

When private information settles the bill : money and privacy in Google's market for smartphone applications

We shed light on a money-for-privacy trade-off in the market for smartphone applications (“apps”). Developers offer their apps cheaper in return for greater access to personal information, and consumers choose between lower prices and more privacy. We provide evidence for this pattern using data on 300,000 mobile applications which were obtained from the Android Market in 2012 and 2014. We augmented these data with information from Alexa.com and Amazon Mechanical Turk. Our findings show that both the market’s supply and the demand side consider an app’s ability to collect private information, measured by their use of privacy-sensitive permissions: (1) cheaper apps use more privacy-sensitive permissions; (2) installation numbers are lower for apps with sensitive permissions; (3) circumstantial factors, such as the reputation of app developers, mitigate the strength of this relationship. Our results emerge consistently across several robustness checks, including the use of panel data analysis, the use of selected matched “twin”-pairs of apps and the use of various alternative measures of privacy-sensitiveness

Money and privacy : Android market evidence

We study the role of privacy in the market for mobile applications. For such programs used with smartphones and tablet PCs a very important market has emerged. Yet, neither the role of privacy on that market is well understood, nor do we have empirical evidence regarding its role therein. We exploit data on 300,000 mobile applications and almost 600 “applications-pairs” to analyze both sides of this market: First, we analyze the price that application suppliers charge for more privacy. Second, we study how users’ installations are related to the “personal data greediness” of mobile applications. We provide the first empirical evidence on the main assumptions of recent early models on suppliers’ and consumers’ strategies in this market. Our results show that (1) consumers take it into account when applications request rights to collect private information and (2) suppliers ask for more rights if they offer an app for free than if they offer it for a fee

Hawking Radiation for Non-minimally Coupled Matter from Generalized 2D Black Hole Models

It is well known that spherically symmetric reduction of General Relativity (SSG) leads to non-minimally coupled scalar matter. We generalize (and correct) recent results to Hawking radiation for a class of dilaton models which share with the Schwarzschild black hole non-minimal coupling of scalar fields and the basic global structure. An inherent ambiguity of such models (if they differ from SSG) is discussed. However, for SSG we obtain the rather disquieting result of a negative Hawking flux at infinity, if the usual recipe for such calculations is applied.Comment: 8 page

Mobile applications and access to private data : the supply side of the Android ecosystem

We analyze the data collection strategies of 65,000 developers in the market for mobile applications and track 300,000 applications over four years. Many apps belong to developers with multiple apps. This fact generates variation in the privacy behaviors of the same developer for our analysis. We uncover three stylized facts: First, developers “learn” to use increasingly intrusive data strategies as they become more experienced. Second, intrusive data collection is most likely in apps that target the 13+, and 16+ age category, which raises concerns for the protection of young app consumers. Third, even within developers, critical and atypical permissions predict problematic usage of private user data most successfully. Our findings inform both regulators and scientists who wish to model supply in the market for mobile apps

Universal conservation law and modified Noether symmetry in 2d models of gravity with matter

It is well-known that all 2d models of gravity---including theories with nonvanishing torsion and dilaton theories---can be solved exactly, if matter interactions are absent. An absolutely (in space and time) conserved quantity determines the global classification of all (classical) solutions. For the special case of spherically reduced Einstein gravity it coincides with the mass in the Schwarzschild solution. The corresponding Noether symmetry has been derived previously by P. Widerin and one of the authors (W.K.) for a specific 2d model with nonvanishing torsion. In the present paper this is generalized to all covariant 2d theories, including interactions with matter. The related Noether-like symmetry differs from the usual one. The parameters for the symmetry transformation of the geometric part and those of the matterfields are distinct. The total conservation law (a zero-form current) results from a two stage argument which also involves a consistency condition expressed by the conservation of a one-form matter ``current''. The black hole is treated as a special case.Comment: 3