2,504 research outputs found

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

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    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

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    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

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    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

    Absolute conservation law for black holes

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    In all 2d theories of gravity a conservation law connects the (space-time dependent) mass aspect function at all times and all radii with an integral of the matter fields. It depends on an arbitrary constant which may be interpreted as determining the initial value together with the initial values for the matter field. We discuss this for spherically reduced Einstein-gravity in a diagonal metric and in a Bondi-Sachs metric using the first order formulation of spherically reduced gravity, which allows easy and direct fixations of any type of gauge. The relation of our conserved quantity to the ADM and Bondi mass is investigated. Further possible applications (ideal fluid, black holes in higher dimensions or AdS spacetimes etc.) are straightforward generalizations.Comment: LaTex, 17 pages, final version, to appear in Phys. Rev.

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

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    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

    The Dimensional-Reduction Anomaly in Spherically Symmetric Spacetimes

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    In D-dimensional spacetimes which can be foliated by n-dimensional homogeneous subspaces, a quantum field can be decomposed in terms of modes on the subspaces, reducing the system to a collection of (D-n)-dimensional fields. This allows one to write bare D-dimensional field quantities like the Green function and the effective action as sums of their (D-n)-dimensional counterparts in the dimensionally reduced theory. It has been shown, however, that renormalization breaks this relationship between the original and dimensionally reduced theories, an effect called the dimensional-reduction anomaly. We examine the dimensional-reduction anomaly for the important case of spherically symmetric spaces.Comment: LaTeX, 19 pages, 2 figures. v2: calculations simplified, references adde

    Money and privacy : Android market evidence

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    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

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

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    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

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

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    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
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